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Sweat Rate Calculator
Estimate sweat loss per hour from your weight before and after exercise, workout duration and drinks.
Your estimated sweat rate
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Change the example inputs to calculate.
See the formula and limitations below.
Keep your daily water goal in view. AquaJoy offers one-tap logging, reminders and streaks on iPhone.
Build a water habit with AquaJoy ↗Free download · iPhone · No account neededHow to measure sweat rate
- Weigh yourself before training, after using the bathroom, in dry minimal clothing.
- Record your workout duration and everything you drink.
- After training, towel dry and weigh yourself on the same scale in the same dry clothing state.
- If you urinated during the workout, enter that volume in the optional field.
The filled-in values are examples, not measured personal data. Wet clothing can hide weight loss. Repeat the test in similar conditions to see how consistent the result is.
Sweat rate formula
Sweat loss (L) ≈ weight before (kg) − weight after (kg) + drinks (L) − urine (L).
Sweat rate (L/h) = sweat loss ÷ exercise hours.
For example: 70 kg before, 69.5 kg after, 500 mL consumed and no urine over 60 minutes gives approximately 1 L of sweat loss and 1 L/h. We use 1 kg of mass change as roughly 1 L of fluid.
This field estimate ignores food consumed, respiratory losses and other mass changes. Long sessions, eating during exercise and imprecise scales reduce its accuracy.
Sweat rate is not a drinking prescription
A measured sweat rate helps you understand one workout. It does not mean you must drink that exact amount every hour. Weather, intensity and clothing can change the next result. Drinking beyond your losses can also be harmful.
This tool estimates sweat volume, not sodium loss, electrolyte needs or medical dehydration. If your weight increased during exercise, reconsider your drinking plan rather than drinking more. Seek medical care if you feel unwell, confused or have severe symptoms.
Keep your daily goal separate
AquaJoy tracks your daily water habit; it does not measure sweat or prescribe an athletic hydration plan. For a general daily estimate, try the water intake calculator. For bottle sizes, use the oz to mL converter.
Frequently asked questions
What is sweat rate?
Sweat rate is estimated sweat volume lost per hour of exercise. This tool expresses it in liters per hour and US fluid ounces per hour.
How do I calculate sweat rate for running?
Subtract your post-run weight from your pre-run weight in kilograms, add liters consumed, subtract urine volume and divide by running time in hours. Use dry weigh-ins and the same scale.
Why do you add the water I drank?
Drinking increases your post-workout weight and hides some fluid loss. Adding the consumed volume back helps estimate the sweat that left your body.
Should I drink exactly my sweat rate?
Not automatically. The result describes one session’s estimated losses, not a prescribed drinking rate. Use your conditions, thirst and qualified guidance to plan hydration.
Does this calculate electrolyte or sodium loss?
No. Sweat sodium concentration varies independently of sweat volume. This tool cannot infer it from your weight change.
Why is my calculated sweat loss negative?
A negative estimate means the inputs do not support a positive sweat-loss calculation. Check units, weigh-ins, drinks and urine entries. Wet clothing or inaccurate measurements can also affect the result.
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Sources and method
By Bruno Martins, creator of AquaJoy. Updated October 8, 2026. Informational tool; not a substitute for professional advice.