Free Online Water Intake Calculator
Estimate a daily hydration goal based on weight and activity.
The baseline uses 35 ml per kg of body weight, with adjustments for exercise, climate, caffeine, and alcohol. Food also contributes water, so this is a drinking-fluid target.
This is an estimate. Needs vary with health conditions, pregnancy, medication, and individual sweat rates. Thirst and pale yellow urine are practical day-to-day guides.
About the Water Intake Calculator
Hydration advice is often reduced to "eight glasses a day", but fluid needs depend on body size, activity, climate, and what else you drink. This calculator builds a personal estimate from body weight, then adjusts it for exercise minutes, climate, caffeine, and alcohol. It reports the result in litres, 250 ml cups, and US fluid ounces so you can use whichever measure your bottles use.
How the estimate is built
The baseline is 35 ml of fluid per kilogram of body weight per day. Exercise adds roughly 350 ml for every 30 minutes of activity, reflecting sweat losses. The climate setting scales the baseline and exercise amount from 5% to 20% to account for heat and humidity. Caffeinated drinks add a small allowance of 30 ml each, and alcoholic drinks add about 240 ml each because alcohol increases urine output. The final number is a target for drinks, not total water intake, since food typically supplies another 20% of daily fluid.
Reading the result sensibly
Drinking too much water is possible, although rare. Spread your intake across the day rather than consuming a large amount at once, and drink more around exercise. Urine colour is a practical check: pale straw usually indicates good hydration, while dark yellow suggests you should drink more. People with heart, kidney, or liver conditions, and anyone taking diuretics, should follow medical advice rather than a generic calculator.
Frequently asked questions
Does coffee count toward hydration?
Yes, coffee and tea contribute to fluid intake. The calculator adds a small allowance for caffeinated drinks rather than subtracting them, which reflects current evidence that moderate caffeine does not cause meaningful dehydration.
Should I drink more in summer?
Yes. Hot and humid weather increases sweat losses, which is why the climate setting raises the target. If you are exercising in heat, add extra fluid and electrolytes.
Is this suitable for children or pregnant people?
No. Children, pregnant people, and people with medical conditions have different fluid needs. Use this tool as general information and consult a healthcare professional for personal advice.