Water Intake Calculator
A daily water intake estimate based on your body weight, exercise, and climate.
Last updated
How to work out how much water to drink
- Enter your body weight in kg or lb.
- Add how many minutes you exercise a day, and tick the box if it’s hot or humid where you are.
- Read your estimated daily water intake.
About this estimate
The baseline is a commonly cited rule of thumb — about 35 mL per kg of body weight — plus roughly 12 mL for every minute of exercise (in the range of the 350–700 mL per 30–60 minutes often recommended for moderate activity), plus a flat 500 mL if you're in a hot or humid climate where sweat losses run higher. This includes water from food and other drinks, not just what you drink from a glass, and it's a starting point, not a target to hit exactly every day.
Nothing entered here is sent to a server — the entire calculation runs as JavaScript in your browser tab.
Questions about drinking water
How much water should I drink a day?
A common rule of thumb is about 35 ml per kg of body weight, so roughly 2.5 litres for a 70 kg adult, plus more for exercise and hot weather.
Does tea, coffee or food count?
Yes. The estimate includes water from all drinks and from food, which provides a good share of most people’s intake, not only glasses of water.
Is the 8 glasses a day rule right?
It’s a rough guide rather than a scientific rule. Needs vary with size, activity, climate and health; being thirsty and having dark urine are signs to drink more.
Can I drink too much water?
Yes, though it’s rare: drinking very large amounts quickly, for example during long endurance events, can dilute the body’s salt. If you have kidney or heart problems, follow your doctor’s advice on fluids.