Water Intake Calculator
A daily water target from body weight, exercise, climate and pregnancy or breastfeeding
100% free. Runs entirely in your browser - your files and data never leave your device and nothing is uploaded to any server.
Units
Climate
Extra
Food also supplies water. Thirst, urine colour and medical conditions (kidney, heart, hyponatremia risk) matter more than any formula.
Estimates only. Not medical advice and not a diagnosis. Talk to a clinician about your own numbers. Base is 35 ml per kg, plus 350 ml per 30 minutes of exercise.
About this tool
A common planning figure is 35 ml of water per kilogram of body weight, plus extra for exercise, heat, pregnancy or breastfeeding. Food also contains water. Pale-yellow urine and thirst are better day-to-day guides than any litre target, and some heart or kidney conditions need a fluid limit. Forcing gallons of water can cause hyponatremia. Estimates only. Not medical advice.
How to use this tool
- Enter body weightKilograms or pounds. The formula converts internally.
- Add exercise minutes and climateThis model adds 350 ml per 30 minutes of exercise and 500 ml on hot or humid days.
- Read litres, US fl oz and 250 ml glassesSpread drinks through the day rather than chugging a huge volume at once.
How much water should I drink a day?
A common planning figure is 35 ml of water for every kilogram of body weight. Someone who weighs 70 kg would aim for about 2.45 litres - roughly 10 glasses of 250 ml - and more on days with exercise or hot weather. In the UK, the NHS Eatwell Guide suggests 6 to 8 glasses of fluid a day as a general rule.
All drinks count, including tea, coffee and milk, and food provides some water too. Pale-yellow urine is a good sign you are drinking enough. People with heart or kidney conditions may be told to limit fluids, so follow your own doctor’s advice.
Key features
- Scales with weight instead of a fixed eight glasses.
- Exercise, climate and pregnancy or breastfeeding extras.
- Litres, millilitres, US fl oz and 250 ml glasses.
- A cap so the page will not suggest more than 6 litres.
Common uses
- A first daily target when someone asks "how much water should I drink".
- Extra water on a hot training day.
- A pregnancy extra of 300 ml in this model, which is a sketch, not a prescription.
Tips for better results
- Urine that is pale straw is a better check than hitting a litre number.
- Caffeine and alcohol still count as fluid but they are not a reason to skip water.
- If a clinician has limited your fluids, ignore this page.
Mistakes to avoid
- Chugging 3 litres in an hour before a weigh-in or a race.
- Ignoring thirst because an app said 4 litres.
- Using this as treatment for oedema, heart failure or kidney disease.
Frequently asked questions
It can land close for a smaller adult. This page scales with weight and activity instead of a fixed eight.
Yes. Hyponatremia is real in endurance events and in people who force gallons of water. Do not chase a number past thirst if a clinician has limited your fluids.
Yes, water in food and other drinks contributes. The litre target here is a total-fluid sketch, not "plain water only".
A common guide is around 400-800 ml extra per hour of exercise, more in heat or with heavy sweating. Weighing yourself before and after a long session shows roughly how much fluid you lost.
Thirst, dark-yellow urine, headaches, tiredness and dizziness are common signs. Older adults feel thirst less, so a regular drinking routine matters more for them.
Tie it to things you already do: a glass after waking, one with each meal and one at each break. Keeping a bottle on your desk makes a bigger difference than any reminder app.