XP TRACKERWater intake calculator
A common rule of thumb is about 30 to 35 ml of water per kilogram of body weight a day, more when you sweat. Enter your weight, how long you exercise and how warm it is, and get a daily estimate in litres, fluid ounces and glasses.
Your daily water estimate
Please read: this is a rough estimate for healthy adults. Water needs vary with body size, climate, activity and health. If you have kidney, heart or other conditions, take medicine that affects fluid balance, or are pregnant or breastfeeding, ask your doctor what is right for you.
How the calculator works
It starts from a widely used rule of thumb: 30 to 35 ml of water per kilogram of body weight per day. The middle value, 33 ml, gives the headline number. On top of that it adds about 350 ml for each 30 minutes of exercise and 250 or 500 ml for warm or hot weather.
Example: a 70 kg person with 30 minutes of exercise on a mild day gets 70 x 33 = 2,310 ml, plus 350 ml, for about 2.7 litres. The range runs from 2.45 to 2.8 litres.
Those totals include water from food. Fruit, vegetables, soup, yoghurt and cooked grains all carry water, and food usually provides about a fifth of what people take in. That is why the tool also shows a "from drinks" figure. Tea, coffee, milk and other drinks count as well as plain water.
How it compares with official figures
Health bodies give reference values for total water from drinks and food together. The European Food Safety Authority (2010) set adequate intakes of 2.0 litres a day for adult women and 2.5 litres for adult men. The US National Academies (2004) gave higher figures, about 2.7 litres for women and 3.7 litres for men. These are averages for groups of people, not a target anyone has to hit.
Turning a number into a habit
- Attach water to things you already do. A glass when you wake up, one with each meal, one when you sit down to work. That alone is four or five glasses.
- Keep a bottle in sight. A 500 ml or 750 ml bottle makes counting easy: four refills of 500 ml is 2 litres.
- Front-load the day. Drinking most of it before late afternoon means fewer trips to the bathroom at night.
- Use simple signs. For most healthy adults, rarely feeling thirsty and pale yellow urine suggest you are drinking enough.
Our drinking water habit guide covers this in more depth, and habit stacking explains the "after I do X, I drink a glass" trick.
Limits of this estimate
Body-weight rules are simple on purpose. They do not know how much you sweat, what you eat, your altitude, or your health. Larger bodies do not always need proportionally more water, so the estimate can run high for people with a high body weight. Your doctor's advice always comes first.
Try it today
Fill a bottle now, note how many refills your estimate means, and drink the first glass before you close this page.
Questions people ask
How much water should I drink a day?
It depends on your body, activity, climate and health. A widely used rule of thumb is 30 to 35 ml per kg of body weight, which is about 2 to 2.5 litres for a 70 kg adult, counting water from food. Thirst and pale yellow urine are useful everyday signs for most healthy adults.
Is 8 glasses of water a day right?
Eight glasses of 250 ml is 2 litres, which is close to many people's needs. It was never a precise medical rule, and drinks like tea, coffee and milk count toward your total too.
Does coffee or tea count toward water intake?
Yes, for most people. They are mostly water. Caffeine has a mild effect on urine output, but regular coffee and tea drinkers still keep most of the fluid. Plain water is the simplest choice for the rest.
How much water do I need when I exercise?
This calculator adds about 350 ml for every 30 minutes of exercise. Real sweat losses vary a lot between people and conditions. In long or hot sessions, sip during the session rather than drinking a lot at once afterwards.
Can you drink too much water?
Yes. Drinking very large amounts in a short time can lower the sodium in your blood, which is dangerous. Spread your water through the day and do not force down far more than you are thirsty for. If you have a health condition, ask your doctor what amount is right for you.
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