Water Intake Calculator
Enter your weight, how active you are and the climate you are in. You get a daily fluid target in millilitres, litres, ounces and cups. Nothing is stored and there is no sign-up.
Calculator
Used only to pick the baseline adequate-intake figure.
Drink about
2 740 ml
2.7 litres · 93 oz · 12 cups
That is fluid you drink. Food supplies roughly 20 percent more on top.
How this is calculated
The starting point is the adequate intake set by the National Academies of Sciences, Engineering, and Medicine: about 3.7 litres of total water a day for men and 2.7 litres for women. Those figures cover total water, including the water in food, which is commonly put at around 20 percent of intake. This calculator reports the drinking portion, so it subtracts that share.
Body weight is then applied as a heuristic of 30 to 35 ml per kilogram, blended with the baseline rather than replacing it, so a very light or very heavy person does not get an absurd number. Activity adds roughly 350 ml per 30 minutes of exercise. A hot or humid climate adds about 500 ml.
It is an estimate for healthy adults, not a clinical calculation. Thirst and urine colour are better day-to-day signals than any formula. If you have a heart, kidney or liver condition, or you are pregnant or breastfeeding, follow your clinician's advice rather than this page.
Hitting the number is the hard part
Knowing your target takes a minute. Remembering to drink through a working day is the actual problem. WaterDrop is our iPhone app for that: one tap to log, reminders that skip your quiet hours, and it syncs to Apple Health.
Common questions
How much water should I drink a day?
The National Academies of Sciences, Engineering, and Medicine set an adequate intake of about 3.7 litres of total water a day for men and 2.7 litres for women. Total water includes what you get from food, which is roughly 20 percent of intake for most people, so the amount you actually drink is lower than those numbers. Body size, activity and climate move the target substantially, which is what this calculator adjusts for.
Does coffee or tea count toward water intake?
Yes. Caffeinated drinks contribute to daily fluid intake. The mild diuretic effect of caffeine does not offset the fluid the drink itself provides at typical intakes.
Is 8 glasses a day correct?
It is a rule of thumb, not a clinical guideline. Eight 8-ounce glasses is about 1.9 litres, which sits below the adequate intake figures for most adults and ignores body size, activity and climate entirely. It is easy to remember, which is most of why it persists.
Can you drink too much water?
Yes. Drinking far more than the body can excrete can dilute blood sodium, a condition called hyponatraemia. It is uncommon but it is a real risk in endurance sport. This calculator gives a general estimate for healthy adults and is not medical advice. Anyone with a heart, kidney or liver condition, or who is pregnant, should follow their clinician’s guidance instead.
This page is information, not medical advice.