About this calculator
This sweat rate calculator estimates how much fluid you lost per hour during a specific workout, practice, or race simulation. It uses the common field method based on body-weight change, fluid intake, urine output, and exercise duration.
Use the result as a training planning estimate, not a diagnosis. Sweat rate changes with heat, humidity, clothing, fitness, acclimatization, intensity, and body size. Repeating the test in different conditions is more useful than relying on one result.
Uses the standard field method: sweat loss equals body-mass change plus fluid consumed minus urine produced, divided by exercise duration. Interpret results with context, heat exposure, sodium needs, and overhydration risk.
Activated — educational sports hydration estimate
Educational estimate only; not a diagnosis, prescription, or treatment plan.
Formula and method
Sweat loss (mL) = body-weight loss converted to mL + fluid consumed during exercise − urine produced during exercise. Sweat rate (L/hour) = sweat loss in liters ÷ exercise duration in hours. This assumes 1 kg body mass is approximately 1 liter of fluid for field hydration planning.
Limitations and when not to rely on this result
- Educational estimate only; not a diagnosis, prescription, or treatment plan.
- Result depends on accurate inputs and may not apply to complex medical situations.
- Use clinician judgment, local guidance, and urgent care pathways when symptoms are severe.
Frequently asked questions
How do I calculate sweat rate? +
Measure body weight before and after exercise, track fluid consumed, subtract urine produced, then divide the estimated sweat loss by exercise duration. This calculator does those unit conversions for you.
Should I drink exactly my sweat rate during exercise? +
Not always. The result helps estimate losses, but drinking plans should account for thirst, gut tolerance, sodium needs, heat, event length, and avoiding weight gain from overdrinking.
Why include urine output? +
Urine produced during the session is fluid lost from the body but not sweat. Subtracting it helps estimate sweat loss more accurately.
What is a high sweat rate? +
Many athletes fall around 0.5–2.0 L/hour depending on conditions, but values can vary widely. Very high results should be repeated and interpreted with heat, sodium, and medical context.
Can this diagnose dehydration or heat illness? +
No. It is a training estimate. Confusion, fainting, chest pain, severe weakness, inability to cool down, or suspected heat illness needs urgent medical attention.