Water Intake Calculator
A common estimate is 35 ml of water per kg of body weight plus 350 ml for every 30 minutes of exercise, so a 70 kg adult who exercises 30 minutes a day should drink about 2.8 L (95 fl oz). The National Academies' adequate intake is about 3.7 L of total water a day for men and 2.7 L for women.
By the Calculators With Steps team · Updated November 10, 2026 · How we check our math
- Millilitres
- 2,800 ml
- US cups (240 ml)
- 11.7
- Fluid ounces (US)
- 95 fl oz
- Glasses (250 ml)
- 11.2
- National Academies adequate intake
- 3.7 L total waterfrom all drinks and food; about 80% (3.0 L) usually comes from drinks
- Baseline (35 ml per kg)2.45 L
- Exercise0.35 L
Step-by-step working
- Baseline: 70 kg × 35 ml = 2,450 ml
- Exercise: 30 min ÷ 30 × 350 ml = 350 ml
- Total = 2,800 ml = 2.8 L = 11.7 cups = 95 fl oz
This counts all drinks (water, milk, tea, coffee), not water in food. Let thirst and pale-yellow urine guide you, and don't force down more than about 1 litre an hour. People with heart failure, kidney disease or on fluid restriction should follow their doctor's limit.
How to use the water intake calculator
- Choose Metric or US units and your sex.
- Enter your body weight and the minutes of sweaty exercise you do on a typical day.
- Pick your climate. If you are a woman who is pregnant or breastfeeding, select it.
The result shows how much to drink per day in litres, millilitres, US cups (240 ml), fluid ounces and 250 ml glasses, how that total is built up, and the National Academies’ adequate intake for comparison.
Water intake formula
The calculator estimates drinks (water and other beverages), not the water in food:
Daily water (ml) = 35 × weight (kg) + exercise + climate + pregnancy or breastfeeding
- Baseline: 35 ml per kg of body weight, the upper end of the 30 to 35 ml/kg rule dietitians commonly use for healthy adults.
- Exercise: 350 ml for every 30 minutes, or 500 ml in hot weather, to replace sweat.
- Hot or humid climate: an extra 500 ml a day.
- Pregnancy: an extra 300 ml a day. Breastfeeding: an extra 700 ml, roughly the water in a day’s breast milk.
Worked example
A 70 kg man who exercises 30 minutes a day:
| Mild climate | Hot climate | |
|---|---|---|
| Baseline (70 × 35 ml) | 2,450 ml | 2,450 ml |
| Exercise (30 minutes) | 350 ml | 500 ml |
| Climate | 0 ml | 500 ml |
| Total | 2,800 ml (2.8 L) | 3,450 ml (3.45 L) |
| US cups (240 ml) | 11.7 | 14.4 |
| Fluid ounces | 95 fl oz | 117 fl oz |
If he trains for an hour instead, the mild-climate total rises to 3,150 ml. In US units a 155 lb man gets the same answer, 95 fl oz, because 155 lb is 70.3 kg.
Water intake by body weight
Baseline amounts before exercise, heat or pregnancy:
| Body weight | Water per day | Fluid ounces |
|---|---|---|
| 50 kg (110 lb) | 1.75 L | 59 fl oz |
| 60 kg (132 lb) | 2.1 L | 71 fl oz |
| 70 kg (154 lb) | 2.45 L | 83 fl oz |
| 80 kg (176 lb) | 2.8 L | 95 fl oz |
| 90 kg (198 lb) | 3.15 L | 107 fl oz |
| 100 kg (220 lb) | 3.5 L | 118 fl oz |
Per-kilogram rules run high for people with a lot of body fat, because fat holds little water. If you weigh over 100 kg, the National Academies figure below is a better guide.
What the National Academies recommend
In 2004 the US National Academies set adequate intakes for total water, which includes drinks and the water in food, for adults aged 19 and over:
| Group | Total water a day | About 80% from drinks |
|---|---|---|
| Men | 3.7 L | 3.0 L |
| Women | 2.7 L | 2.2 L |
| Pregnant women | 3.0 L | 2.4 L |
| Breastfeeding women | 3.8 L | 3.0 L |
These are the average intakes of healthy, well-hydrated people, not strict requirements. The report notes that most people meet their needs by drinking when thirsty, and that heat and long periods of activity raise needs. Fruit, vegetables, soups, dal and curd all add water too.
Common rules of thumb
- “8 glasses a day”: 8 × 8 fl oz = 64 fl oz, about 1.9 L. Easy to remember, but below what most men need.
- “Half your body weight in ounces”: 0.5 fl oz per lb works out to about 32.6 ml per kg, close to our baseline. A 155 lb person would drink 77.5 fl oz (2.29 L).
Are you drinking enough?
Pale yellow urine and rarely feeling thirsty are good signs. Dark urine, headaches, tiredness and dizziness can point to dehydration, especially in heat or during long exercise. Drink steadily through the day rather than in big gulps, and avoid forcing down more than about a litre an hour. People with heart failure, kidney disease or a fluid restriction should follow their doctor’s limit.
To estimate how much you burn when you exercise, see the calories burned calculator. For daily food targets, use the calorie calculator.
Water Intake Calculator: frequently asked questions
How much water should I drink a day?
Most adults need roughly 30 to 35 ml per kg of body weight from drinks, plus extra for exercise and heat. A 70 kg man who exercises 30 minutes a day in a mild climate needs about 2.8 litres. The National Academies' adequate intake is 3.7 litres of total water for men and 2.7 litres for women, about 80% of it from drinks.
How do I calculate water intake by body weight in kg?
Multiply your weight in kilograms by 35 ml. A 60 kg person needs about 60 × 35 = 2,100 ml (2.1 litres) a day before exercise, and a 70 kg person about 2,450 ml. Add about 350 ml for every 30 minutes of exercise.
Do tea, coffee and milk count toward water intake?
Yes. The National Academies count all beverages, including tea and coffee, toward total water. Water is still the best everyday choice because it has no calories or added sugar.
How much water should I drink when pregnant or breastfeeding?
Add about 300 ml a day in pregnancy and about 700 ml while breastfeeding. A 60 kg woman who doesn't exercise needs about 2.4 litres a day when pregnant and 2.8 litres when breastfeeding. The National Academies' adequate intakes are 3.0 and 3.8 litres of total water.
What is the maximum amount of water you can drink in a day?
There is no fixed daily maximum for healthy people; the risk comes from drinking too much too fast. Drinking well over a litre an hour for several hours can dilute the sodium in your blood (hyponatremia), which can be dangerous.
Is 3 litres of water a day too much?
Not for most healthy adults. It is close to what a 70 kg man needs in hot weather with 30 minutes of exercise, which this calculator puts at 3.45 litres. A smaller, inactive person needs less, but healthy kidneys handle the extra easily if it is spread through the day.
Is the 8 glasses a day rule right?
Eight 8-ounce glasses is 64 fl oz, about 1.9 litres. It is a reasonable floor for many adults but is not based on research, and it is less than most men need. Your weight, activity and climate matter more.
How we checked this page: every figure in the examples and FAQs above is produced by this calculator and verified by automated tests against known answers, and the rules and rates come from the sources below. Last updated . Spotted a problem? Tell us.