How much water do you need?
European food safety authorities recommend a total water intake of about 2.0 liters a day for women and 2.5 liters for men, from drinks and food combined, in a mild climate with moderate activity. Active people, larger people and anyone in hot weather need more.
Our calculator focuses on what you drink, and scales it to your body and your day.
How the water intake calculator works
Daily baseline = 33 ml × body weight (kg), adjusted for your daily activity+ exercise: about 0.7 L per hour of training+ hot or humid weather: about 0.5 L
- Body weight sets your baseline. A 70 kg (154 lb) person starts at about 2.3 liters.
- Activity level adds 5–20% for more active days, since moving more raises your fluid losses.
- Exercise time adds fluid to replace sweat. People sweat anywhere from 0.5 to over 2 liters an hour, so we use a moderate average.
- Heat adds extra because sweating increases even at rest.
Hydration for training
- Before: drink a glass or two of water in the couple of hours before you train, so you start hydrated.
- During: for sessions under an hour, water is enough. For long or very sweaty sessions, a drink with sodium helps you retain fluid.
- After: weigh yourself before and after training. Drink about 1.25–1.5 liters for every kilogram lost.
How to tell if you are drinking enough
- Urine colour: pale yellow is a good sign; dark yellow suggests you need more.
- Thirst: for most healthy adults in daily life, thirst is a reliable guide.
- Body weight: a sudden drop of more than 1–2% after training means you lost more fluid than you replaced.
Research behind this calculator
- EFSA Panel on Dietetic Products, Nutrition and Allergies (2010). Scientific opinion on dietary reference values for water. EFSA Journal.
- American College of Sports Medicine (2007). Exercise and fluid replacement. Medicine & Science in Sports & Exercise.
Last updated September 21, 2026.