Sweat Rate Calculator
Work out how much you sweat per hour so you can plan hydration for training and racing.
How to use the sweat rate calculator
- Weigh yourself before and after a measured workout.
- Enter both weights, the fluid you drank, and the duration.
- Click Calculate to get your sweat rate and a fluid target.
Why sweat rate is individual
Sweat rates vary widely with fitness, heat acclimation, intensity and genetics. Measuring yours removes the guesswork and helps prevent both dehydration and over-drinking.
Why sweat rate is so individual
Sweat rates vary enormously with fitness, heat acclimatisation, intensity, body size, and genetics, ranging from under half a litre to well over two litres per hour. Generic hydration advice cannot account for that spread, which is why measuring your own rate, by weighing before and after a run, removes the guesswork.
Turning your sweat rate into a hydration plan
Once you know how much you lose per hour, you can aim to replace most of it during long efforts, typically 400-800 ml per hour but personalised to your number. Over-drinking is as risky as under-drinking, so the goal is to match losses, not to drink as much as possible. Repeat the test in different conditions, because heat dramatically raises your rate.
Frequently asked questions
How do you calculate sweat rate?
Sweat rate equals body-weight loss plus fluid consumed, divided by exercise time. A 1 kg drop after drinking 500 ml in an hour is a 1.5 L/hour sweat rate.
How much should I drink while running?
Aim to replace most of what you lose. Many runners need 400–800 ml per hour, but your own sweat rate — and the heat — should set the number.
How do I measure my sweat rate?
Weigh yourself before and after a measured workout, add any fluid you drank, and divide by the time. A 1 kg drop after drinking 500 ml in an hour is a 1.5 L/hour sweat rate.
How much should I drink while running?
Aim to replace most of what you lose, often 400-800 ml per hour, guided by your measured sweat rate and the conditions rather than a fixed rule.
Should I drink to thirst or to a schedule?
For most runs, drinking to thirst works well. For long or hot efforts where losses are high, a plan based on your sweat rate helps you stay ahead of dehydration.
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