Fitness · Nutrition & Calorie Planning

Water Intake Calculator

Calculate your recommended daily water intake based on body weight and activity level.

5 inputs7 min read

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Water Intake Calculator

Method

Weightkg

Activity Level

Climate

For informational and educational purposes only. Results should not be used as a substitute for professional advice. Always consult a qualified professional before making important decisions. Terms of service

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Hydration targets

Daily water amount in litres, glasses, and per-exercise top-up

Daily total

—

Glasses

—

glasses

During exercise

—

ml/hour

Incl. food

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Beverages

—

Beverage glasses

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glasses

About Water Intake Calculator

7 min read

Water Intake Calculator: Find Your Daily Hydration Target by Weight, Activity, and Climate

TL;DR: Most adults need 35 ml of water per kilogram of body weight per day as a baseline, which is 2.45 L for a 70 kg person. Active adults add 400–600 ml per hour of moderate exercise, and people in hot climates add a further 500–1,000 ml daily. About 20% of daily water comes from food, so the beverage-only target is roughly 80% of the total. This calculator adjusts for body weight, activity level, and climate and returns your daily target in both litres and cups.

Why "Eight Glasses a Day" Is Not a Formula
Eight Situations Where Your Water Target Changes
How Daily Water Targets Are Calculated
Using the Calculator: Five Steps to Your Hydration Target
Two Water Intake Calculations, Fully Worked
Six Hydration Mistakes That Are Easy to Miss
FAQ
Assumptions and Notes
After You Have Your Number
Further Reading

Why "Eight Glasses a Day" Is Not a Formula

Eight glasses. Roughly 2 litres. The advice has been repeated so often that most people assume it came from a clinical study. It did not. The figure traces back to a 1945 US Food and Nutrition Board recommendation that included a critical qualifying sentence almost no one remembers: "Most of this quantity is contained in prepared foods." The standalone 2-litre number was never the full recommendation.

The actual Institute of Medicine Adequate Intake values, published in 2005, are 3.7 L per day total water for adult men and 2.7 L per day for adult women. These totals include water from all sources: beverages, plain water, and the water naturally present in food. Food contributes approximately 19–20% of total water intake for most people eating a diet with adequate fruits and vegetables. The beverage-only target for a sedentary adult woman is therefore closer to 2.16 L per day, not 2.0 L, and for a sedentary adult man approximately 2.96 L.

Neither figure accounts for body weight, exercise, heat, altitude, or pregnancy. A 100 kg man and a 60 kg woman both described as "sedentary adult females and males" have meaningfully different fluid requirements. The formula that produces personalised targets accounts for weight first, then adjusts for every factor that increases fluid loss.

Plug your weight, activity level, and climate into the calculator above for your specific daily target.

Eight Situations Where Your Water Target Changes

You exercise for 60 minutes or more at moderate to high intensity. Sweat rate during exercise ranges from 0.5 to 2.0 L per hour depending on body size, temperature, and exercise intensity. A 75 kg runner in moderate conditions loses approximately 1.0–1.2 L per hour. Adding 400–600 ml per 30 minutes of exercise to the baseline daily target covers this loss for most people training at moderate intensity in temperate conditions. Heavier athletes or those training in heat need the upper end of this range.
You live or work in a climate where the average temperature exceeds 30°C. Heat increases sweat production even at rest. A person sitting outdoors in 35°C heat may lose 500–700 ml more fluid per day than the same person in a 20°C office, without any deliberate exercise. People newly arrived in a hot climate typically require 2–4 weeks of heat acclimatisation before sweat rate and electrolyte concentration normalise; during this period, fluid needs are 20–30% higher than after full acclimatisation.
You are pregnant. Pregnancy increases total water requirements by approximately 300 ml per day above the standard female baseline. The Institute of Medicine recommends a total of 3.0 L per day during pregnancy (approximately 2.4 L from beverages). Amniotic fluid is almost entirely water and is continuously exchanged; adequate hydration supports amniotic fluid volume, foetal circulation, and the increased maternal blood volume that develops across the second trimester.
You are breastfeeding. Breast milk is approximately 87% water, and producing it increases total daily water requirements by 700 ml above the standard baseline. The Institute of Medicine recommends 3.8 L per day total water during breastfeeding (approximately 3.1 L from beverages). Inadequate hydration during breastfeeding reduces milk volume before it significantly affects milk quality, making low milk output one of the first practical signs of insufficient fluid intake.
You consume 3 or more caffeinated or alcoholic drinks per day. Caffeine has a mild diuretic effect at intakes above approximately 300 mg per day (roughly 3 standard cups of coffee). Alcohol suppresses antidiuretic hormone (ADH) production, increasing urine output by 100–150 ml per standard drink above what would otherwise be excreted. People consuming alcohol regularly or at high volumes need to add 200–300 ml of additional water per standard drink to offset this loss.
You are over 65. Thirst sensation diminishes significantly with age: adults over 65 experience thirst at a higher level of dehydration than younger adults, meaning the body's natural signal to drink is delayed. Older adults can reach 2–3% dehydration (enough to impair cognitive function and physical performance) without feeling meaningfully thirsty. Scheduled drinking at regular intervals, rather than relying on thirst, is the most reliable approach for this group.
You have been ill with vomiting or diarrhoea. Each episode of vomiting or diarrhoea can result in 200–500 ml of fluid loss beyond normal daily losses. Diarrhoeal illness specifically causes losses of water and electrolytes (sodium, potassium, chloride) simultaneously, and replacing water alone without electrolytes can worsen the sodium imbalance. Oral rehydration salts or electrolyte solutions rather than plain water are the most effective replacement for losses above 1 litre.
You are at altitude above 2,500 metres. At high altitude, respiration rate increases to compensate for lower oxygen partial pressure. This faster, deeper breathing expels significantly more water vapour per day than breathing at sea level: approximately 500–800 ml additional daily water loss at altitudes above 3,000 m. Altitude also suppresses thirst while increasing losses, the same combination that makes dehydration a consistent problem for hikers and climbers who do not deliberately increase fluid intake.

How Daily Water Targets Are Calculated

Your daily water target starts with a body-weight-based baseline and adds adjustments for each factor that increases fluid loss above the resting rate.

Step 1: Baseline water target
  Method 1 (weight-based): 35 ml × body weight (kg)
  Method 2 (Institute of Medicine AI):
    Males 19+:   3.7 L total / day (3.0 L beverages)
    Females 19+: 2.7 L total / day (2.16 L beverages)

Step 2: Exercise adjustment
  Add 400–600 ml per 30 min of moderate exercise
  Add 600–1,000 ml per 30 min of vigorous exercise

Step 3: Climate adjustment
  Temperate (15–25°C):  no adjustment
  Warm (25–30°C):       + 300–500 ml/day
  Hot (30–35°C):        + 500–750 ml/day
  Very hot (35°C+):     + 750–1,000 ml/day

Step 4: Special condition adjustment
  Pregnancy:      + 300 ml/day above female baseline
  Breastfeeding:  + 700 ml/day above female baseline
  Alcohol (per standard drink): + 200–300 ml
  Age 65+:        multiply baseline × 1.1 (10% buffer for
                  reduced thirst sensitivity)

Step 5: Subtract food water contribution
  Beverages-only target = total target × 0.80
  (food provides approximately 20% of total water intake)

Institute of Medicine Adequate Intake by Age and Sex

Group	Age	Total Water (L/day)	Beverages (L/day)
Children	1–3 years	1.3	1.0
Children	4–8 years	1.7	1.4
Girls	9–13 years	2.1	1.7
Boys	9–13 years	2.4	1.9
Girls	14–18 years	2.3	1.8
Boys	14–18 years	3.3	2.6
Women	19–50 years	2.7	2.2
Men	19–50 years	3.7	3.0
Women	50+ years	2.7	2.2
Men	50+ years	3.7	3.0
Pregnant	any	3.0	2.4
Breastfeeding	any	3.8	3.1

Urine Colour Hydration Guide

Colour	Hydration Status	Action
Pale straw / very light yellow	Well hydrated	Maintain current intake
Light yellow	Adequately hydrated	No change needed
Medium yellow	Mildly under-hydrated	Drink 250–500 ml now
Dark yellow / amber	Dehydrated	Drink 500 ml now, increase daily target
Brown / orange	Severely dehydrated or medical issue	Seek medical attention

Water Content in Common Foods

Food	Serving	Water Content	Contribution to Daily Intake
Cucumber	100 g	95 ml	~95 ml
Watermelon	150 g	137 ml	~137 ml
Strawberries	150 g	136 ml	~136 ml
Cooked oatmeal	240 g	190 ml	~190 ml
Whole orange	130 g	112 ml	~112 ml
Cooked chicken breast	150 g	106 ml	~106 ml
White rice (cooked)	200 g	150 ml	~150 ml

Genetic variation in aquaporin proteins, which regulate water transport across cell membranes, means individuals differ in how efficiently the kidneys concentrate urine and retain water. Variants in the AQP2 gene (aquaporin-2, the primary renal water channel) affect urine concentrating ability and therefore how much water is lost in urine at a given level of hydration. People with reduced AQP2 function tend to produce larger volumes of dilute urine and may need 10–15% more daily fluid to maintain the same hydration status as those with standard aquaporin function. Thirst sensitivity also has a heritable component, with twin studies estimating approximately 30% heritability in the thirst response threshold.

The main limitation of weight-based formulas is that they do not account for body composition. Body fat tissue contains approximately 10% water by mass, while lean muscle tissue contains approximately 75% water. A 90 kg person who is 35% body fat has far lower absolute water requirements per kilogram than a 90 kg person who is 15% body fat, because less of their total mass is metabolically active water-dependent tissue. The formula overestimates requirements slightly for people with higher body fat percentages.

Using the Calculator: Five Steps to Your Hydration Target

Enter your body weight. Use your current weight in kilograms or pounds. The calculator applies the 35 ml/kg baseline formula to generate a personalised starting point that differs from the one-size-fits-all 2 L figure.
Select your activity level. Choose the option that best describes your average day including both structured exercise and general movement. A person who walks 10,000 steps daily but does no structured training is Lightly Active, not Sedentary. The activity selection adjusts for the additional fluid lost through elevated respiration and perspiration during movement.
Select your climate. If you live in a region with consistent heat or spend meaningful time outdoors in warm conditions, select the appropriate climate band. This adjustment adds 300–1,000 ml depending on temperature range, reflecting increased insensible water loss through sweat and respiration in warm environments.
Read your total daily water target and your beverages-only target separately. The total figure includes water from food. The beverages-only number is what you actually need to drink. For most people on a balanced diet with adequate fruits and vegetables, food covers approximately 500–700 ml of the total, and the drink target reflects the remainder.
Convert to cups or bottles for practical tracking. A standard 250 ml cup means a 2.5 L beverage target is 10 cups per day. A 750 ml water bottle means the same target is 3.3 refills. Translating litres into the specific container you carry removes the mental arithmetic from hitting the target each day.

Non-obvious insight: Thirst is not a reliable early indicator of dehydration. By the time most adults feel thirsty, they are already at approximately 1–2% dehydration, which is sufficient to reduce short-term memory performance by 7–8% and aerobic exercise capacity by 5%. A practical alternative to thirst-based drinking is time-based drinking: one glass of water with each meal and one glass mid-morning and mid-afternoon covers 1.25 L of a 2.5 L daily target through habit rather than relying on the thirst signal.

Two Water Intake Calculations, Fully Worked

Example 1: Male Competitive Cyclist, Age 38, Training in Summer Heat

Diego is a 78 kg amateur cyclist who trains 5 days per week. He rides for 90 minutes per session and lives in southern Spain where summer temperatures regularly reach 34–37°C. He wants to set a precise daily target for both rest days and training days.

Baseline (35 ml/kg):
  = 35 × 78 = 2,730 ml (2.73 L)

Climate adjustment (hot, 34–37°C):
  + 900 ml/day

Rest day total:
  = 2,730 + 900 = 3,630 ml (3.63 L total)
  Beverages: 3,630 × 0.80 = 2,904 ml (2.9 L)

Training day — add exercise adjustment (90 min vigorous):
  = 3 × 700 ml (vigorous, per 30 min) = 2,100 ml
  Training day total: 3,630 + 2,100 = 5,730 ml
  Beverages: 5,730 × 0.80 = 4,584 ml (4.6 L)

Day Type	Total Water Target	Beverages Only	Cups (250 ml)
Rest day	3.63 L	2.90 L	11.6 cups
Training day	5.73 L	4.58 L	18.3 cups

Diego's actionable plan: on training days, front-load hydration. Drink 500 ml in the 2 hours before riding, carry a 750 ml bottle and consume it during the 90-minute session (targeting 500 ml per 45 minutes), and drink 750 ml in the 2 hours after finishing. This covers 2,000 ml of the training-day adjustment within a 4-hour window around the session. The remaining 2.58 L for the day comes from regular drinking across meals and between sessions. On rest days, the 2.9 L beverage target is achievable across 4 meals and 4–5 stand-alone glasses of water.

Example 2: Breastfeeding Woman, Age 31, Temperate Climate

Amara is a 63 kg new mother, 6 weeks postpartum and exclusively breastfeeding. She lives in the UK and has a desk job she returned to part-time. She wants to confirm whether her current informal drinking habits are meeting her elevated postpartum hydration needs.

Baseline (35 ml/kg):
  = 35 × 63 = 2,205 ml (2.21 L)

Breastfeeding adjustment:
  + 700 ml/day

Climate (temperate, UK):
  + 0 ml adjustment

Light activity (desk job, short daily walks):
  + 200 ml adjustment

Total:
  = 2,205 + 700 + 200 = 3,105 ml (3.11 L total)
  Beverages: 3,105 × 0.80 = 2,484 ml (2.48 L)

Component	Value
Baseline (35 ml/kg)	2,205 ml
Breastfeeding adjustment	+700 ml
Activity adjustment	+200 ml
Total daily target	3,105 ml
Beverages-only target	2,484 ml
Cups (250 ml)	9.9 cups

Amara's 2.48 L beverages-only target is meaningfully higher than the standard 2.16 L female baseline she may have been using. Her actionable approach: drink a full glass of water at every breastfeeding session (typically 8–12 per day in the early weeks), which alone contributes 2.0–3.0 L and makes meeting the target a direct function of feeding frequency rather than a separate tracking task. Pale straw urine colour is the easiest daily confirmation that the target is being met.

Six Hydration Mistakes That Are Easy to Miss

Using the "8 glasses" rule regardless of body weight or activity. Two litres suits a sedentary 60 kg woman in a temperate climate reasonably well. Applied to an 85 kg man who trains 5 days per week in summer heat, it falls 2.0–2.5 L short of actual requirements on training days. The weight-based formula (35 ml/kg) before exercise and climate adjustments provides a more accurate baseline than any flat-number rule, and the difference is not trivial: a 2 L shortfall on a training day represents approximately 2.5% dehydration, enough to reduce endurance performance by 10–15%.

Counting coffee and tea as neutral when consuming 3+ cups per day. Moderate caffeine intake (up to 300 mg per day, roughly 3 cups of filter coffee) is largely offset by the water content of the beverage and does not produce meaningful net fluid loss in habituated drinkers. Above 300 mg per day, the diuretic effect becomes relevant. At 4–5 cups of coffee, net fluid loss from caffeine may be 150–250 ml above the baseline urinary output that plain water would produce. This does not mean coffee dehydrates; it means it is a less efficient hydrator than plain water above the 3-cup threshold.

Drinking large volumes at once rather than across the day. The kidneys can process approximately 0.8–1.0 L of water per hour. Drinking 1.5 L in a single session to "catch up" after a dry morning results in approximately 500–700 ml of excess being excreted as dilute urine within 2 hours, while the remaining morning deficit persists. Distributing intake across 8–10 drinking occasions through the day produces substantially better tissue hydration than the same total consumed in 2–3 large volumes.

Not increasing fluid intake during illness with fever. Core body temperature rises approximately 0.5–1°C per hour of untreated fever. Each 1°C rise in body temperature increases insensible water loss through skin and respiration by approximately 10–12% above baseline. A moderate fever of 38.5°C sustained for 24 hours increases daily water requirements by approximately 500–800 ml above the normal target. Most people drink less when feeling unwell, widening the gap further.

Relying on sports drinks as the primary hydration source during low-intensity activity. Sports drinks containing 6–8% carbohydrate (glucose or fructose) are designed to replace glycogen and electrolytes during sessions lasting 60+ minutes at moderate to high intensity. During lower-intensity activity (walking, yoga, light cycling), the carbohydrate load adds 120–240 kcal per 500 ml bottle without a meaningful performance benefit. Plain water with a small electrolyte supplement is more appropriate for sessions under 60 minutes. Treating sports drinks as general hydration beverages adds 240–480 kcal per day from liquid alone.

Ignoring hydration needs during air travel. Aircraft cabin humidity is typically 10–20%, far below the 40–60% humidity of most indoor environments. At this humidity level, insensible water loss through respiration increases significantly: approximately 50–100 ml per hour above the rate in a normal indoor setting. A 10-hour long-haul flight in low cabin humidity produces an additional 500–1,000 ml of water loss beyond what the standard daily target accounts for. Drinking 250 ml per hour of flight in addition to the standard daily target compensates for this loss.

Assumptions and Notes

Margin of error: The 35 ml/kg body-weight formula produces targets within ±10–15% of individual measured requirements for most healthy adults. Actual daily water needs vary with ambient temperature, humidity, physical exertion, metabolic rate, diet composition, and individual kidney function. The formula is a planning guide; urine colour monitoring over 1–2 weeks of following the target provides the most reliable feedback on whether the calculated amount is appropriate for an individual's actual physiology.
Professional disclaimer: Water intake targets from this calculator are based on Institute of Medicine Adequate Intake values and American College of Sports Medicine hydration guidelines. They are for informational and planning purposes only and do not constitute medical advice. People with kidney disease, heart failure, liver cirrhosis, hyponatremia history, diabetes insipidus, or other conditions affecting fluid balance should consult a physician before using any general hydration formula to set their daily intake target.

After You Have Your Number

Diego's 4.6 L beverage target on training days was not a surprise once the formula was run — it confirmed what his performance data had been suggesting for months. Amara's 2.48 L target was higher than she expected and explained the fatigue she had attributed to interrupted sleep rather than dehydration.

Both numbers were specific enough to act on. A general recommendation to "drink more water" is not.

Enter your weight and activity level above and get your daily hydration target now.

About the Water Intake.

How much water should I drink per day?

The evidence-based baseline is 35 ml per kilogram of body weight per day. For a 70 kg adult this is 2.45 L total, or approximately 1.96 L from beverages (food covers the remaining 20%). Active adults add 400–600 ml per 30 minutes of moderate exercise. The Institute of Medicine sets Adequate Intake at 3.7 L per day for men and 2.7 L per day for women, including water from food.

Is 2 litres of water a day enough?

For a sedentary woman under 65 in a temperate climate, 2 L from beverages covers the standard recommendation of 2.16 L. For most men, active women, or anyone exercising regularly, 2 L falls short. A 75 kg man who trains 60 minutes per day needs approximately 2.9–3.4 L from beverages on training days. Use the weight-based formula (35 ml/kg + activity adjustment) rather than a flat 2 L rule.

How do I know if I am drinking enough water?

Urine colour is the most practical daily indicator. Pale straw or very light yellow means well hydrated. Dark yellow or amber means dehydration and requires 500+ ml immediately. Urine should be light yellow for the majority of daily voids; consistently dark urine despite drinking indicates a persistent shortfall. Morning urine is naturally more concentrated and is not representative of whole-day hydration status.

Does coffee count toward daily water intake?

Yes, with a qualification. Moderate coffee consumption (up to 3 cups per day, approximately 300 mg caffeine) does not cause net fluid loss in habituated drinkers and counts toward total daily fluid intake. Above 300 mg per day, a mild diuretic effect reduces the net contribution of each additional cup. Tea counts similarly. Alcohol does not count; it produces a net fluid loss of 100–150 ml per standard drink due to ADH suppression.

How much water should I drink when exercising?

The American College of Sports Medicine recommends 5–7 ml per kg of body weight in the 4 hours before exercise, and 400–800 ml per hour during exercise depending on sweat rate, body size, and conditions. After exercise, drink 1.5 L for every kilogram of body weight lost during the session. Weighing before and after a session (dry, without clothing) is the most accurate way to measure sweat loss and calculate replacement needs.

Can you drink too much water?

Yes, but it is rare in healthy adults. The kidneys can excrete up to 15 L per day, so normal drinking cannot produce overhydration. Hyponatremia (water intoxication) occurs when water intake greatly exceeds kidney excretion capacity over a short period, typically seen in endurance athletes who drink more than 1.5 L per hour without sodium replacement. Healthy adults consuming water at the rate of thirst or a body-weight formula are at no risk of overhydration.

How much water should I drink to lose weight?

Drinking water does not directly cause fat loss, but adequate hydration supports it in two practical ways: drinking 500 ml of water 30 minutes before a meal reduces total calorie intake at that meal by approximately 13% in controlled trials, and even mild dehydration (1–2%) reduces the motivation and capacity for physical activity. The standard daily target (35 ml/kg body weight) is appropriate regardless of fat loss goal; no additional water above this is needed purely for weight loss purposes.

How much water do pregnant women need?

The Institute of Medicine recommends 3.0 L of total water per day during pregnancy, approximately 2.4 L from beverages. This is 300 ml above the standard female baseline of 2.7 L. Requirements increase further in the second and third trimesters as blood volume expands and amniotic fluid volume grows. Pregnant women in hot climates or who exercise during pregnancy should apply the standard climate and activity adjustments on top of the pregnancy baseline.

Does drinking water help with headaches?

Dehydration is a known trigger for tension headaches. At 1–2% dehydration, cerebral blood volume decreases slightly, which is thought to activate pain-sensitive intracranial structures. Drinking 500 ml of water at the onset of a dehydration-related headache produces measurable relief within 30 minutes in most cases. Not all headaches are dehydration-related; persistent or severe headaches should be evaluated medically regardless of hydration status.

How much water should children drink?

Water needs for children scale with age and body size. The Institute of Medicine recommends 1.3 L per day total for children aged 1–3, 1.7 L for ages 4–8, and 2.1–2.4 L for ages 9–13 depending on sex. Children are more vulnerable to dehydration than adults because their body surface area to mass ratio is higher, increasing proportional water loss. Children also have a less reliable thirst response than young adults; scheduled drinking during school hours and outdoor activity is more reliable than waiting for thirst. ---

Step 1: Baseline water target Method 1 (weight-based): 35 ml × body weight (kg) Method 2 (Institute of Medicine AI): Males 19+: 3.7 L total / day (3.0 L beverages) Females 19+: 2.7 L total / day (2.16 L beverages) Step 2: Exercise adjustment Add 400–600 ml per 30 min of moderate exercise Add 600–1,000 ml per 30 min of vigorous exercise Step 3: Climate adjustment Temperate (15–25°C): no adjustment Warm (25–30°C): + 300–500 ml/day Hot (30–35°C): + 500–750 ml/day Very hot (35°C+): + 750–1,000 ml/day Step 4: Special condition adjustment Pregnancy: + 300 ml/day above female baseline Breastfeeding: + 700 ml/day above female baseline Alcohol (per standard drink): + 200–300 ml Age 65+: multiply baseline × 1.1 (10% buffer for reduced thirst sensitivity) Step 5: Subtract food water contribution Beverages-only target = total target × 0.80 (food provides approximately 20% of total water intake)

Group

Age

Total Water (L/day)

Beverages (L/day)

Children

1–3 years

1.3

1.0

Children

4–8 years

1.7

1.4

Girls

9–13 years

2.1

1.7

Boys

9–13 years

2.4

1.9

Girls

14–18 years

2.3

1.8

Boys

14–18 years

3.3

2.6

Women

19–50 years

2.7

2.2

Men

19–50 years

3.7

3.0

Women

50+ years

2.7

2.2

Men

50+ years

3.7

3.0

Pregnant

any

3.0

2.4

Breastfeeding

any

3.8

3.1

Colour

Hydration Status

Action

Pale straw / very light yellow

Well hydrated

Maintain current intake

Light yellow

Adequately hydrated

No change needed

Medium yellow

Mildly under-hydrated

Drink 250–500 ml now

Dark yellow / amber

Dehydrated

Drink 500 ml now, increase daily target

Brown / orange

Severely dehydrated or medical issue

Seek medical attention

Food

Serving

Water Content

Contribution to Daily Intake

Cucumber

100 g

95 ml

~95 ml

Watermelon

150 g

137 ml

~137 ml

Strawberries

150 g

136 ml

~136 ml

Cooked oatmeal

240 g

190 ml

~190 ml

Whole orange

130 g

112 ml

~112 ml

Cooked chicken breast

150 g

106 ml

~106 ml

White rice (cooked)

200 g

150 ml

~150 ml

Baseline (35 ml/kg): = 35 × 78 = 2,730 ml (2.73 L) Climate adjustment (hot, 34–37°C): + 900 ml/day Rest day total: = 2,730 + 900 = 3,630 ml (3.63 L total) Beverages: 3,630 × 0.80 = 2,904 ml (2.9 L) Training day — add exercise adjustment (90 min vigorous): = 3 × 700 ml (vigorous, per 30 min) = 2,100 ml Training day total: 3,630 + 2,100 = 5,730 ml Beverages: 5,730 × 0.80 = 4,584 ml (4.6 L)

Day Type

Total Water Target

Beverages Only

Cups (250 ml)

Rest day

3.63 L

2.90 L

11.6 cups

Training day

5.73 L

4.58 L

18.3 cups

Baseline (35 ml/kg): = 35 × 63 = 2,205 ml (2.21 L) Breastfeeding adjustment: + 700 ml/day Climate (temperate, UK): + 0 ml adjustment Light activity (desk job, short daily walks): + 200 ml adjustment Total: = 2,205 + 700 + 200 = 3,105 ml (3.11 L total) Beverages: 3,105 × 0.80 = 2,484 ml (2.48 L)

Component

Value

Baseline (35 ml/kg)

2,205 ml

Breastfeeding adjustment

+700 ml

Activity adjustment

+200 ml

Total daily target

3,105 ml

Beverages-only target

2,484 ml

Cups (250 ml)

9.9 cups

Water Intake Calculator

Water Intake Calculator

AI Assistant

Hydration targets

About Water Intake Calculator

Water Intake Calculator: Find Your Daily Hydration Target by Weight, Activity, and Climate

Table of Contents

Why "Eight Glasses a Day" Is Not a Formula

Eight Situations Where Your Water Target Changes

How Daily Water Targets Are Calculated

Using the Calculator: Five Steps to Your Hydration Target

Two Water Intake Calculations, Fully Worked

Example 1: Male Competitive Cyclist, Age 38, Training in Summer Heat

Example 2: Breastfeeding Woman, Age 31, Temperate Climate

Six Hydration Mistakes That Are Easy to Miss

Assumptions and Notes

After You Have Your Number

Further Reading

About the Water Intake.

Water Intake Calculator

Water Intake Calculator

AI Assistant

Hydration targets

About Water Intake Calculator

Water Intake Calculator: Find Your Daily Hydration Target by Weight, Activity, and Climate

Table of Contents

Why "Eight Glasses a Day" Is Not a Formula

Eight Situations Where Your Water Target Changes

How Daily Water Targets Are Calculated

Using the Calculator: Five Steps to Your Hydration Target

Two Water Intake Calculations, Fully Worked

Example 1: Male Competitive Cyclist, Age 38, Training in Summer Heat

Example 2: Breastfeeding Woman, Age 31, Temperate Climate

Six Hydration Mistakes That Are Easy to Miss

Assumptions and Notes

After You Have Your Number

Further Reading

About the Water Intake.