Water Intake Calculator (How Much Water Should I Drink?)
Daily water to drink from the National Academies' Adequate Intakes for men, women, pregnancy and breastfeeding, plus an allowance for exercise.
Inputs
- From drinks
- 3.3 L (13 glasses of 250 ml)
- Total water, food included
- 4.0 L (16 glasses of 250 ml)
- Adequate Intake (Man, 19 or over)
- 3.7 L total, 3.0 L from drinks
- Exercise allowance
- 30 min × 0.5 L an hour = 0.25 L
- Weight-based rule of thumb (35 mL/kg)
- 2.5 L (10 glasses of 250 ml)
- 2% of body weight
- 1.4 kg — lose more than this in a workout and you drank too little
- The Adequate Intake is a typical intake for healthy people, not a minimum. Thirst, heat, illness and medicines change what any one person needs.
Use this calculator on your own site
Free embed
- Two lines of HTML, unlimited views
- Shows a small CalculateEveryday bar, with a credit link under the calculator
What each Water Intake input means
- You are
- The National Academies set separate Adequate Intakes for men and women aged 19 and over, and higher ones for pregnancy and breastfeeding.
- Weight
- Used for the 2% sweat-loss line and the weight-based comparison. The National Academies figures themselves do not change with weight.
- Exercise a day
- Minutes of exercise on a typical day. Each hour adds 0.5 L; heavy sweaters in heat can lose three times that, so weigh yourself before and after a session to find your own rate — each kilogram lost is about a litre.
Water Intake formula
Water to drink = Adequate Intake from beverages (by sex, pregnancy or breastfeeding) + exercise minutes ÷ 60 × 0.5 L
The best-known figures for daily water come from the National Academies, which set Adequate Intakes for total water — drinks plus the water in food — at 3.7 litres a day for men and 2.7 litres for women aged 19 and over, 3.0 litres in pregnancy and 3.8 litres when breastfeeding. About a fifth of that usually comes from food, so the part to drink is 3.0, 2.2, 2.3 and 3.1 litres. These are typical intakes of healthy people, not minimums, and they do not depend on body weight. Exercise adds sweat losses on top: the American College of Sports Medicine puts typical sweat rates at about 0.4 to 1.8 litres an hour, so the page adds 0.5 litres per hour of exercise, near the low end, and shows the 2% weight-loss line ACSM uses to judge whether you drank enough during a session. The weight-based rule of 35 mL per kilogram, which many calculators use, is shown for comparison. All drinks count, including tea, coffee and milk.
Water Intake worked example
A man who exercises 30 minutes a day: the Adequate Intake from drinks is 3.0 L, and half an hour at 0.5 L an hour adds 0.25 L, so the target is 3.3 L — about 13 glasses of 250 ml. Counting food, his total water is about 4.0 L. The 35 mL/kg rule would say 2.5 L for his 70 kg, noticeably less, and 2% of his weight is 1.4 kg, the most he should lose in a single workout.
More Water Intake examples
A woman who works out for an hour: 2.2 L from drinks plus 0.5 L for the hour is 2.7 L, or 91 fl oz, about 11 cups. If she weighs 150 lb, losing more than 3 lb during that hour would mean she drank too little.
During pregnancy the Adequate Intake rises to 3.0 L of total water, of which 2.3 L is from drinks — about nine glasses a day before any exercise.
Where the Water Intake calculator can give the wrong answer
- The Adequate Intake describes what healthy people typically consume; the report set no upper limit and no single requirement, because healthy kidneys handle a wide range. Thirst is a reliable guide for most healthy adults on most days.
- Heat, altitude, fever, vomiting and diarrhoea all raise needs, sometimes by litres. The exercise allowance here is a planning figure, not a replacement for drinking to thirst in hot conditions.
- Too much is possible. Drinking far more than you sweat during long endurance events can dilute blood sodium (hyponatremia); ACSM advises against drinking so much that you gain weight during exercise.
- Kidney and heart conditions, and some medicines, mean a doctor may set a fluid limit lower than any figure here. Follow that instead.
- Glass and cup counts are rounded: 250 ml glasses in metric, 8 fl oz cups in US units.
Spotted a mistake? Tell us
Water Intake reference table
| Group | Total water a day | From drinks |
|---|---|---|
| Men | 3.7 L (about 125 fl oz) | 3.0 L (about 13 cups) |
| Women | 2.7 L (about 91 fl oz) | 2.2 L (about 9 cups) |
| Pregnancy | 3.0 L | 2.3 L (about 10 cups) |
| Breastfeeding | 3.8 L | 3.1 L (about 13 cups) |
Water Intake FAQ
- About 3.0 litres (13 cups) of drinks for men and 2.2 litres (9 cups) for women, by the National Academies' Adequate Intakes, plus more for exercise and heat. Those figures assume food supplies roughly another fifth of your water.
- A common rule is 30–35 mL per kilogram — about 2.5 litres at 70 kg — and the page shows it for comparison. The National Academies did not set intakes by weight, so the main figure here follows their sex-based values instead, which are higher than the weight rule for most people.
- Yes. The National Academies count all beverages, including caffeinated ones, toward total water, and found that caffeinated drinks contribute to it like any other. Milk, juice and soup count too.
- Eight 8-ounce glasses is 1.9 litres, a little under the National Academies' 2.2 litres of drinks for women and well under the 3.0 for men. It was never an official rule, but it is a reasonable minimum to aim for if you also eat water-rich food.
- Roughly what you sweat out. ACSM puts typical sweat rates at 0.4 to 1.8 litres an hour; the page adds 0.5 litres an hour as a starting point. To find your own rate, weigh yourself before and after an hour's session: each kilogram lost is about a litre to replace.
- Yes — hyponatremia from over-drinking is rare but real, mostly in long endurance events where people drink on a schedule well beyond their sweat losses. Gaining weight during a long run or ride is the warning sign.