Water Intake Calculator

How much water do you need? See the daily amount from European guidelines, and weigh yourself before and after training to find out how much you sweat.

Your details

Sex
Workout sweat check (optional)
kg
kg
L
min

Use the same scale and dry clothing. Use the toilet before the first weigh-in and repeat the check another time if you urinate during the workout.

Your results

How to use it

  1. Pick your sex, and for women, whether you're pregnant or breastfeeding.
  2. Read your daily total. About 80% of it usually comes from drinks, the rest from food.
  3. For the optional sweat check, weigh yourself right before and after a workout (same scale and dry clothing, after using the toilet before the first weigh-in), and enter what you drank and how long you trained.
  4. Read your estimated sweat rate and weight change. If you urinated between weigh-ins, repeat the check another time because this estimate assumes no urine loss.

How it's calculated

Daily water. The European Food Safety Authority (EFSA, 2010) set these adequate intakes for adults, for total water from drinks and food:

Group Litres a day
Men 2.5
Women 2.0
Pregnant 2.3 (+0.3)
Breastfeeding 2.7 (+0.7)

They apply at moderate temperatures and activity levels. About 80% of total water usually comes from drinks and 20% from food (Institute of Medicine, 2005), so the calculator shows 80% as the drinks part. In imperial units, 1 litre = 33.8 US fl oz.

Sweat check. Following the ACSM position stand on exercise and fluid replacement (Sawka et al., 2007):

  • Sweat lost (litres) = weight before − weight after + fluid drunk during (1 kg ≈ 1 litre).
  • Sweat rate = sweat lost ÷ hours trained.
  • Bodyweight lost (%) = (before − after) ÷ before × 100. The ACSM advises keeping this under 2%, because larger losses can hurt performance.
  • Weight gain can signal overdrinking. The calculator flags it and also flags loss above 2% of starting weight.
  • A sweat or drinking rate over 4 L/hour prompts a measurement check. This is an input limit for the calculator.

Limits. Heat, humidity, clothing and fitness all change sweat rates, so repeat the check in different conditions. People with heart or kidney conditions should follow their doctor’s advice on fluids.

Sources

  1. EFSA Panel on Dietetic Products, Nutrition, and Allergies (2010). Scientific Opinion on Dietary Reference Values for water. EFSA Journal, 8(3), 1459.
  2. Institute of Medicine (2005). Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. Washington, DC: National Academies Press.
  3. American College of Sports Medicine, Sawka, M. N., Burke, L. M., Eichner, E. R., Maughan, R. J., Montain, S. J., & Stachenfeld, N. S. (2007). American College of Sports Medicine position stand: exercise and fluid replacement. Medicine & Science in Sports & Exercise, 39(2), 377–390.
  4. McDermott, B. P., et al. (2017). National Athletic Trainers’ Association Position Statement: Fluid Replacement for the Physically Active. Journal of Athletic Training, 52(9), 877–895.

Questions

How much water should I drink a day?

European guidelines (EFSA) set 2.5 litres a day for men and 2.0 litres for women, from drinks and food together. With about 80% from drinks, that's roughly 2 litres of drinks for men and 1.6 litres for women, on a normal day.

Do I need more on training days?

Yes. The daily amount assumes moderate activity and temperature. Sweat losses vary a lot from person to person, which is why the sweat check measures yours instead of guessing.

Why weigh myself before and after training?

Weight change plus what you drank gives an estimate of sweat loss if you did not urinate between weigh-ins and clothing stayed dry. A kilogram of water is about a litre.

Can I drink too much water?

Yes. Drinking far more than you sweat, especially during long endurance events, can dilute the salt in your blood. Weight gain during exercise can be a sign of overdrinking. Avoid forcing extra fluids.

Updated November 9, 2026.