Water Intake Calculator
Estimate how much water to drink each day for your body and activity.
How to use the Water Intake Calculator
- Enter your body weight.
- Enter your average daily exercise in minutes.
- See your estimated daily water target.
Water (ml) ≈ weight(kg) × 35 + 350 ml per 30 min of exercise
About the Water Intake Calculator
This calculator applies a simple, widely repeated rule of thumb: roughly 35 ml of water per kilogram of body weight per day, plus about 350 ml for every 30 minutes of exercise you enter. It converts that to litres and to glasses of 250 ml. That is all it does — there is no formula here with the standing of Mifflin-St Jeor behind it, so treat the output as a rough reference figure rather than a requirement.
Some honesty about hydration advice is overdue. The famous “8 glasses a day” rule has no strong evidence base — it appears to have been passed along until it sounded official. A large share of your daily water arrives through food, especially fruit and vegetables, and tea, coffee, milk and juice all count too. Individual needs vary enormously with climate, altitude, body size, illness and how hard you are working.
For most healthy people with normal kidneys, thirst is a reasonable guide, and urine that is pale rather than dark is a decent everyday check. If you have a heart or kidney condition, are pregnant, or have been told to limit or increase fluids, follow that advice rather than a number produced by multiplying your weight by 35 — this is an estimate, not a substitute for a doctor or dietitian. See also the calorie calculator and the BMR calculator.
Frequently asked questions
Do I really need to drink this much water?
Not necessarily. It is a rule-of-thumb figure, not a medical requirement. It also ignores the water you get from food and other drinks, which is a substantial share of most people’s daily intake.
Is the “8 glasses a day” rule true?
There is no strong evidence for it. It is a memorable number that got repeated until it sounded authoritative. Needs vary far too much between people and climates for any single figure to be right for everyone.
Do tea and coffee count?
Yes. Tea, coffee, milk, juice and soft drinks are mostly water and contribute to your intake. Water is simply the cheapest and calorie-free option.
How do I know if I am drinking enough?
For most healthy people, thirst is a reasonable guide, and pale rather than dark urine is a useful everyday check. Both beat following a calculated target.
Can you drink too much water?
Yes, though it is uncommon. Drinking very large volumes in a short period can dilute blood sodium dangerously. Spreading intake across the day rather than forcing it to hit a target is sensible.
Guides & articles about this tool
How Much Water Should You Drink a Day?
The simplest answer to how much water per day is drink enough so you’re not thirsty and your pee stays pale. This piece covers what counts towards that to…