Water Intake Calculator
Estimate how much water to drink each day from your weight, how much you exercise, and whether you live somewhere hot.
Water a day
3.2 litres
- In 250 ml glasses
- 13 glasses
Aim for about 3.2 litres of fluid a day, roughly 13 glasses. Pale yellow urine is a good sign you're drinking enough.
How it's worked out
- Base need
70 kg × 33 ml2.31 L - Exercise
30 min ÷ 30 × 350 ml0.35 L - Heat0.5 L
- Total3.16 L
- A general guide. Food provides about a fifth of daily water. People with kidney or heart conditions should follow their doctor's advice.
- Don't drink more than about 1 litre in any hour.
How the estimate works
Water = 33 ml × weight + 350 ml per 30 minutes of exercise + 500 ml in hot weather
Weight is counted up to 100 kg and exercise up to 240 minutes, and the total never goes above 6 litres a day. Needs don't keep rising with weight, and drinking too much is dangerous.
Worked example
A 70 kg person who exercises 30 minutes a day in a hot climate needs about 2.31 + 0.35 + 0.5 = 3.2 litres a day, roughly 13 glasses.
Questions people ask
How much water should I drink a day?
A common rule of thumb is about 33 ml per kg of body weight, plus more for exercise and heat. For 70 kg that's about 2.3 litres before exercise. For comparison, EFSA advises 2.0 litres (women) and 2.5 litres (men) of water a day from all drinks and food, and the US National Academies 2.7 and 3.7 litres. Thirst is a good guide for most healthy people.
Can you drink too much water?
Yes. Drinking far more than you sweat can dilute your blood salt (hyponatraemia), which is dangerous. Don't drink more than about 1 litre in any hour. The calculator counts weight up to 100 kg and exercise up to 4 hours a day, and never suggests more than 6 litres a day.
Does tea or coffee count?
Yes, most drinks count towards fluid. Food also provides about a fifth of your daily water.
How do I know I'm drinking enough?
Pale yellow urine and rarely feeling thirsty are good signs. Dark urine or headaches can mean you need more.
About this calculator
Formula and rules last checked 12 November 2026Written and tested by the CalculatorDex teamReport a problem
Sources: EFSA (2010), Scientific Opinion on Dietary Reference Values for water · US National Academies (2004), Dietary Reference Intakes for Water, Potassium, Sodium, Chloride and Sulfate · CDC/NIOSH, Heat Stress: Hydration (Pub. No. 2017-126)