For training
Sweat Rate Calculator
Quick answer
To calculate sweat rate, weigh yourself before and after exercise, add the fluid you drank, subtract any urine, and divide by workout time. The result is your sweat loss in litres per hour. Use it to plan fluids for similar workouts, especially in heat or before a race.
Sweat rate
About 51 fl oz/hour. Estimated sweat loss: 1.5 L.
- During similar workouts
- Sip about 0.4–0.8 L/hour, then adjust for thirst, stomach comfort, and heat.
- After training
- Replace roughly 1.9 L over the next few hours, with sodium if the session was long, hot, or salty.
- Body-mass loss
- You lost about 1.1% of body weight. Try to stay below 2% on race-day practice sessions.
Why sweat rate matters
Sweat rate is the missing number in most hydration advice. Body weight gives you a daily baseline, but sweat rate tells you how fast you lose fluid during a specific sport, pace, and weather pattern. Measure it on a normal workout first, then repeat in hotter conditions.
How to use the result
For similar sessions, drink enough to keep body-mass loss below about 2%, while avoiding the urge to force down more than your stomach can handle. After the session, replace about 125–150% of the remaining fluid loss over the next few hours, with sodium when the session was long, hot, or salty.
Frequently asked
What is a normal sweat rate?
Many athletes fall around 0.5–1.5 L per hour, but the real range is wide. Heat, humidity, intensity, clothing, body size, and acclimation can move your number a lot, which is why measuring beats guessing.
How do I calculate sweat rate?
Weigh yourself before and after exercise, add the fluid you drank, subtract any urine, then divide by workout hours. One kilogram of body-weight loss is treated as about one litre of fluid.
Should I replace 100% of sweat during exercise?
Usually no. Trying to match every drop can upset your stomach and raises over-drinking risk. A better target is to limit body-mass loss to under about 2% and replace the rest after training.
Sources
- 1.American College of Sports Medicine, Exercise and Fluid Replacement — Athletes should start exercise euhydrated, limit body-mass losses during training, and replace fluid and sodium after heavy sweat losses.
- 2.Sawka et al., ACSM Position Stand — Sweat rate varies widely by athlete, heat, intensity, clothing, and acclimation, so pre/post body-weight checks are the practical way to individualise fluid plans.
- 3.Mayo Clinic — General guidance of roughly 2.7–3.7 L of total fluids a day, with thirst and pale-yellow urine as everyday checks.