Sweat rate calculator
Estimate your hourly sweat rate to plan hydration during exercise.
Related tools
All Running & endurance tools →Need Total sweat loss (ml), Sweat rate (ml/hour)? The Sweat rate calculator derives it from Weight before (kg), Weight after (kg), Fluid drunk (ml), Duration (hours) in one step. For instance, with Weight before (kg) = 70, Weight after (kg) = 68.5, Fluid drunk (ml) = 500 and Duration (hours) = 1 it returns Total sweat loss (ml) = 2,000 and Sweat rate (ml/hour) = 2,000.
How to use it
- Enter your values: Weight before (kg), Weight after (kg), Fluid drunk (ml), Duration (hours).
- Read the result instantly: Total sweat loss (ml), Sweat rate (ml/hour).
Frequently asked questions
How does the Sweat rate calculator work?
It takes Weight before (kg), Weight after (kg), Fluid drunk (ml) and Duration (hours) and derives Total sweat loss (ml) and Sweat rate (ml/hour) from them. The calculation is live as you type, so the result updates on every change.
Which values does the calculator ask for?
4 values: Weight before (kg), Weight after (kg), Fluid drunk (ml) and Duration (hours). Nothing else is required — no account, no file upload.
What does a typical calculation look like?
With Weight before (kg) = 70, Weight after (kg) = 68.5, Fluid drunk (ml) = 500 and Duration (hours) = 1, the calculator returns Total sweat loss (ml) = 2,000 and Sweat rate (ml/hour) = 2,000. Those figures come from running this exact tool, so you can reproduce them by entering the same values.
How much does the result change with different inputs?
It moves a lot. Using Weight before (kg) = 77, Weight after (kg) = 75.4, Fluid drunk (ml) = 1,000 and Duration (hours) = 2 instead, Total sweat loss (ml) goes from 2,000 to 2,600 — which is why it is worth testing a few scenarios rather than trusting a single figure.
What does it give for smaller values?
Scaled down to Weight before (kg) = 63, Weight after (kg) = 61.7, Fluid drunk (ml) = 250 and Duration (hours) = 0.5, Total sweat loss (ml) comes out at 1,550. The relationship is worth checking at both ends before you rely on a single result.
When would I actually use this?
Preparing a race: the pace a target time needs, the splits to hold it, and the training zones that sit under it — on foot, and equally on a bike or in a pool, where the same session is measured in watts or in a hundred-metre split instead.
What is the most common mistake?
Scaling a time linearly to a longer distance. A marathon is not two half-marathons; race predictors use an exponent around 1.06 precisely because fatigue is not proportional.
How accurate is it, and what are the limits?
For general guidance only — not medical advice.
What is the difference between the Sweat rate calculator and the Heart rate zones calculator?
This one returns Total sweat loss (ml) and Sweat rate (ml/hour); the Heart rate zones calculator returns Max heart rate (bpm) and Zone 2 — fat burn (bpm). That is the whole difference — open the one whose figure you need.
Is there a tool for the next step?
Target heart rate calculator is the closest one after this: Find your target training heart rate with the Karvonen formula.