Sweat Rate Calculator
Your fluid loss per hour from weight change and fluid drunk during exercise.
Result
Total sweat loss (L)
1.50
Sweat rate (L/h)
1.50
How it works
Your sweat rate is how much fluid you lose per hour of exercise. It is measured with a simple mass balance: weigh yourself before and after a session, add any fluid you drank during it, and divide the total loss by the duration in hours. A one-kilogram drop in body weight corresponds to roughly one litre of sweat. If you lost 0.7 kg over a one-hour run while drinking 0.5 L, your sweat rate is 1.2 L/h — a fairly typical figure, though rates range from under 0.5 to over 2.5 L/h depending on heat, intensity and the individual. Knowing the number turns hydration from guesswork into a plan: aim to replace enough during exercise to limit losses to about 2% of body weight, and rehydrate after with about 1.5× the remaining deficit. Repeat the measurement in different weather — your rate in July can be double your rate in January.
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Frequently asked questions
Why does it matter?
It guides how much to drink during long efforts to avoid dehydration.
When should I test it?
In conditions like your event — heat and intensity change sweat rate a lot.
How much of my sweat loss should I replace while exercising?
Enough to keep weight loss under about 2% of body weight during the session. Most athletes tolerate replacing 60–80% of losses in the moment and complete rehydration afterwards.
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