Water Intake Calculator
Work out how much water to drink a day from your weight, age, exercise and climate, with a drinking schedule.
Enter your weight — your daily water target updates as you type.
- Daily water target
- —
- In litres
- —
- Glasses (250 ml)
- —
- Per waking hour
- —
How it adds up
- Baseline (weight & age)
- —
- Exercise
- —
- Climate
- —
- Pregnancy / breastfeeding
- —
Your drinking schedule
These numbers are a general estimate, not medical advice. Real fluid needs vary with health, medication, kidney or heart conditions and pregnancy — and drinking far more water than you need can be dangerous. Ask a doctor or dietitian before making big changes.
How it works
The calculator starts from the most widely used rule of thumb for daily fluid: about
35 ml per kg of body weight for adults up to 55, dropping to 30 ml/kg between 56
and 65 and 25 ml/kg after 65, because the body holds less water as you age. It then adds
roughly 350 ml for every 30 minutes of exercise, raises the baseline by 10% in warm weather
and 20% in hot or humid weather, and adds 300 ml if you are pregnant or 700 ml if you are
breastfeeding.
The result is shown in millilitres and litres (or fluid ounces and cups in imperial), as a number of glasses, and as a per-waking-hour sip. From your wake-up time and bedtime it also builds a two-hourly drinking schedule you can copy or download. Around a fifth of most people's fluid already comes from food, so treat the target as a ceiling to aim at rather than a quota of plain water. Everything is computed in your browser with plain JavaScript — your weight, age and routine never leave your device, and there are no ads or sign-ups.
Frequently asked questions
How much water should I drink a day?
A common rule of thumb is about 35 ml of fluid per kilogram of body weight for adults up to 55, which works out at roughly 2.45 litres (83 fl oz, or about 10 glasses) for a 70 kg person. The rate drops to about 30 ml/kg between 56 and 65 and 25 ml/kg after 65, because older bodies hold less water. Add roughly 350 ml for every 30 minutes of exercise, 10% in warm weather and 20% in hot or humid weather, plus 300 ml if you are pregnant or 700 ml if you are breastfeeding. This calculator applies all of those adjustments at once and shows the breakdown.
Does coffee, tea and food count towards my water intake?
Yes. Tea, coffee, milk, juice and soft drinks are all mostly water and count towards your fluid total — the old idea that caffeine dehydrates you does not hold at normal drinking amounts. Food contributes too: fruit, vegetables, soup and yoghurt supply roughly a fifth of most people's daily fluid. That means the number here is a target for total fluid, not a quota of plain water on top of everything else you drink, so treat it as a ceiling to aim at rather than a minimum to force down.
Can you drink too much water?
Yes, and it can be serious. Drinking far more than your kidneys can excrete — very roughly a litre per hour for a healthy adult — dilutes the sodium in your blood and can cause hyponatraemia, with headache, nausea, confusion and, in rare cases, seizures. Endurance athletes who over-drink during long events are the classic case. Spread your intake across the day rather than downing large volumes at once, and if you have a kidney, liver or heart condition, or take medication that affects fluid balance, follow your doctor's advice instead of a general calculator. These results are estimates, not medical advice.