Reference scenario: a 70 kg (154 lbs) adult male with an active routine in a temperate climate — the calculator below is prefilled with exactly these inputs. The calculator returns 3.3 L per day for a male reference input and 3.0 L for a female reference input — about 13 and 12 glasses of 250 ml. At the same weight and climate the full range runs from 2.5 L (sedentary) to 3.7 L (very active). Enter your own weight, sex, activity and climate below to replace these reference inputs with your result.
During exercise, your body prioritizes blood flow to muscles and cooling. It temporarily reduces kidney function and digestive activity. Once you stop, your body shifts into recovery mode — and this is when proper rehydration directly affects how well (and fast) you recover.
Dehydration after exercise delays muscle protein synthesis, increases muscle soreness, raises resting heart rate, and impairs glycogen replenishment. In short: if you skip post-workout hydration, you undermine the benefits of the workout itself.
Sports science has established a clear guideline: replace 150% of fluid lost during exercise. The extra 50% accounts for ongoing losses through urine production as your kidneys resume normal function. Here's how to apply it:
For example: if you lose 0.8 kg during a workout, drink 1,200 ml over the next 2–4 hours.
The tool below estimates how much fluid you lost during one exercise session and your sweat rate per hour. It measures; it does not tell you exactly how much to drink.
How to run the test:
Formula: sweat loss = weight before − weight after + fluid drunk − urine passed. Sweat rate = sweat loss ÷ exercise time in hours. About 1 kg of body-weight change corresponds to about 1 litre of fluid. This is the field method used by the CDC and the Korey Stringer Institute (University of Connecticut).
One session, not a permanent number. Your result reflects this session and these conditions. Sweat rate changes with temperature, humidity, intensity, clothing and equipment, heat acclimatization and individual physiology. Repeat the test in the conditions you care about. This tool estimates fluid loss, not sodium loss.
You don't need to replace all lost fluid immediately. Spread your recovery fluids over the next few hours. A practical approach:
For most workouts under 60 minutes at moderate intensity, plain water is perfectly adequate. Your next meal will naturally replace any lost electrolytes. However, in these situations, consider adding electrolytes:
You don't need expensive supplements — a pinch of sea salt in water with a squeeze of lemon provides sodium and potassium naturally.
Monitor these indicators in the hours after exercise: if your urine remains dark yellow 2 hours post-workout, you haven't replaced enough fluid. Persistent thirst, elevated resting heart rate, headache, or unusual fatigue the next day all point to inadequate recovery hydration.
Taking creatine? Research has not set a specific extra amount of water for it — see how much water to drink with creatine.
Begin drinking within 15–30 minutes of finishing your workout. Drink steadily over the next 2–4 hours rather than all at once.
For workouts under 60 minutes, water is sufficient. For intense sessions over 60 minutes or in heat, a drink with electrolytes helps replace lost sodium and potassium.