About the Sweat Rate Calculator
This tool estimates how much fluid you lost during exercise and converts it into an hourly sweat rate. It is useful for runners, cyclists, team-sport athletes, coaches, and anyone planning hydration for training in specific conditions.
How to use this calculator
- Enter your body weight before exercise in kilograms.
- Enter your body weight after exercise in kilograms.
- Enter the amount of fluid consumed during exercise in liters.
- Enter the exercise duration in hours, using decimals if needed.
- Read the sweat rate, total fluid lost, and body weight change shown below the inputs.
How it works
The calculator uses body weight before exercise, body weight after exercise, fluid consumed during exercise, and exercise duration. It treats 1 kg of body mass change as approximately equal to 1 liter of fluid change.
Example calculation
Suppose an athlete weighs 70.0 kg before exercise and 68.8 kg after exercise, drinks 0.5 L during the workout, and exercises for 1.5 hours. Body weight change is 70.0 − 68.8 = 1.2 kg, so total fluid lost is 1.2 + 0.5 = 1.7 L. Sweat rate is 1.7 ÷ 1.5 = 1.13 L/hour.
Frequently asked questions
What is a normal sweat rate during exercise?
Many athletes fall around 0.5 to 1.5 L/hour, but sweat rate varies widely with heat, humidity, exercise intensity, clothing, acclimation, and individual physiology.
Why is fluid consumed added to the weight loss?
Fluid you drank replaced some sweat during the session. Adding it back estimates the total fluid that left your body, not just the net weight loss on the scale.
Can the result be negative?
Yes. If your after-exercise weight plus recorded intake suggests a net gain, the calculator may show negative total fluid loss or sweat rate. This usually means rechecking scale readings, clothing, food intake, or fluid entries.
Should I replace 100% of sweat loss while exercising?
Not always. Hydration needs depend on session length, conditions, stomach tolerance, sodium losses, and goals. These results are educational estimates and not medical or performance advice.