Sweat Rate & Hydration Calculator
Weigh yourself before and after a workout and tell us what you drank. We'll work out how much fluid you lose per hour, and how much to drink to replace it.
Hourly sweat rate
Hydration sorted. Now the workout.
Type the session you’re planning — “90 min easy with 6 x 30 sec strides” — and TextFit turns it into a structured workout on your Garmin, Wahoo, or Apple Watch. No clicking through builders.
Free to start. No account, no sign-up. Works in any language.
How the calculation works
The standard field method for measuring sweat rate, for runners, cyclists, and triathletes alike, is a simple weigh-in protocol: weigh yourself (ideally nude and toweled dry) right before and right after a session. Every kilogram lost is roughly 1,000 ml of fluid. Add back whatever you drank during the workout, subtract any urine output, and divide by the duration — that's your hourly sweat rate.
Why it matters: losing more than about 2% of your body weight to dehydration measurably hurts endurance performance, and thirst lags well behind actual losses. Your sweat rate changes with heat, humidity, and intensity, so retest in different conditions — a summer race plan needs a different bottle strategy than a winter trainer session.