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
Is 8 glasses a day correct?
It is a rule of thumb, not a 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 lasted.
Does coffee or tea count?
Yes. Caffeinated drinks contribute to daily fluid intake. At normal intakes the mild diuretic effect does not cancel out the fluid the drink provides.
Can you drink too much?
Yes. Drinking far more than the body can excrete dilutes blood sodium, a condition called hyponatraemia. It is uncommon, but it is a genuine risk in endurance sport.
This page is information, not medical advice.