How Much Water to Drink
The day's water, plus what training takes out.
The equations were fitted separately for men and women, so they need one of the two. It is the body the formula describes, not an identity.
Optional — weigh yourself to measure your sweat
Without clothes, after towelling off, before drinking. The difference is the sweat you did not replace.
Fill in the fields and the answer appears here.
An estimate from a formula, not a measurement. It does not replace a doctor, a dietitian or a qualified trainer — least of all with a health condition, during pregnancy or breastfeeding, or under 18. With heart or kidney disease, or a doctor's limit on fluids, follow that limit, not this page. Drinking far more than you sweat is harmful too.
How this was worked out
Fill in the fields and the answer appears here.
Guide: The day’s base3 min read
The day’s base
The reference used is the European Food Safety Authority’s (EFSA, 2010): 2.0 litres of total water a day for women and 2.5 for men. About 20% of that comes from food, so what you drink is around 1.6 and 2.0 litres. The “35 ml per kilogram” rule is widely repeated but is not a reference value.
What training adds
During exercise, the American College of Sports Medicine’s guidance is 0.4 to 0.8 litres an hour — more in heat and humidity and for heavy sweaters. The calculator adds that range for the minutes you train.
To swap the average for your own number, weigh yourself without clothes before and after training, towelled dry and before drinking. Every kilogram lost is about a litre of sweat, and replacing it takes 1.25 to 1.5 litres per kilogram over the next hours. Losing more than 2% of your weight in a session already costs performance.
The everyday check, and the limit
Pale yellow urine and little thirst say the sum is about right. Drinking far more than you sweat is harmful too: in long events it can dilute the sodium in the blood. With heart or kidney disease, or a fluid limit from your doctor, that limit is the one that counts. Nothing you type is kept.
How we calculate
Adequate water intake (2010)
total water a day: 2.0 L for women, 2.5 L for men, of which about 80% comes from drinks and 20% from food
Source: EFSA Panel on Dietetic Products, Nutrition, and Allergies. Scientific Opinion on Dietary Reference Values for water. EFSA Journal. 2010;8(3):1459.
Fluids around exercise (2016)
during exercise 0.4 to 0.8 L an hour, more in heat; after, 1.25 to 1.5 L for every kilogram lost
Source: American College of Sports Medicine; Sawka MN, Burke LM, Eichner ER, et al. Exercise and fluid replacement. Med Sci Sports Exerc. 2007;39(2):377-390. Thomas DT, Erdman KA, Burke LM. Nutrition and Athletic Performance. Med Sci Sports Exerc. 2016;48(3):543-568.
Frequently asked questions
How much water should I drink a day?
The European Food Safety Authority puts adequate total water at 2.0 litres a day for women and 2.5 for men, of which about 80% comes from drinks — 1.6 and 2.0 litres — and the rest from food. That is the base before exercise, heat or a large body add to it.
How much water during a workout?
The American College of Sports Medicine's guidance is roughly 0.4 to 0.8 litres an hour, more in heat and for heavier sweaters. The calculator adds that range for the minutes you train.
How do I measure my sweat rate?
Weigh yourself without clothes before training and again after, towelled dry and before drinking. Every kilogram lost is about a litre of sweat; replace it with 1.25 to 1.5 litres over the next hours, because some is lost again as urine.
Is 35 ml per kilogram right?
It is a common rule of thumb, but not a reference value. This page uses the EFSA figures, which are, and adds your training separately so the number moves with what you actually do.
Can you drink too much water?
Yes. Drinking far more than you sweat, especially in long events, can dilute the blood's sodium to dangerous levels. With heart or kidney disease, or a fluid limit from your doctor, follow that limit instead.