How to use
- 1Enter your weight (kg or lb), sex and daily training time.
- 2Pick the training intensity and the weather.
- 3Read your daily fluid target and the training-day drinking plan.
- 4Weigh yourself before and after a session and fill in the sweat test to find your own sweat rate.
How the estimate works
Baseline need is taken as about 35 ml of total water per kg of body weight, raised by 10–20% in hot weather. According to the European Food Safety Authority (EFSA, 2010) roughly 20% of total water comes from food, so the amount to drink is 80% of that baseline. Estimated sweat loss from training is added on top: 0.4, 0.7 and 1.0 L per hour for light, moderate and hard sessions, scaled 0.8–1.6× for the weather. A 70 kg (154 lb) person training moderately for 60 minutes in mild weather should drink about 2.7 L a day.
Before, during and after training
The plan follows the American College of Sports Medicine (ACSM) 2007 position stand on fluid replacement: 5–7 ml per kg about 4 hours before exercise; during exercise enough to keep body-weight loss below 2%, usually 0.4–0.8 L per hour; afterwards 1.25–1.5 L for every kg lost. In long, sweaty sessions over an hour a sports drink with sodium helps. Our guide to drinking during exercise covers this in detail.
Why the sweat test matters
Sweat rates range from about 0.3 to over 2 L per hour between people and conditions — a summer soccer match is not a winter jog. Sweat loss = (weight before − weight after) + fluid drunk − urine; 1 kg lost is roughly 1 L of sweat. If you lose more than 2% of body weight, drink more during training; if you gain weight you are over-drinking, which carries a risk of hyponatremia. With kidney or heart disease, agree fluid targets with your doctor; this tool is not medical advice.
Frequently asked questions
How much water should I drink a day?
EFSA sets an adequate total intake, including food, of 2.5 L for men and 2.0 L for women. People who train should add what they sweat; the calculator does this from your weight and training.
How much water per pound or kg of body weight?
A rough rule is 30–35 ml of total water per kg, about 0.5 fl oz per lb. For 70 kg (154 lb) that is around 2.1–2.45 L, part of which comes from food.
How much should I drink during a workout?
Usually 0.4–0.8 L per hour — a few sips to a glass every 15–20 minutes. The aim is to keep weight loss under 2%.
How do I measure my sweat rate?
Weigh yourself without clothes before and after training, add what you drank, subtract urine and divide by the hours. For example 0.9 kg lost + 0.5 L drunk in an hour = 1.4 L/h.
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