Free field tool
Find your sweat-rate starting point.
Use a representative training run to estimate fluid loss per hour. No login, no email, and no paywall—just a practical number to test before your next long race.
Training-session sweat-rate calculator
Weigh before and after a steady, representative run in similar clothing. Record what you drank; include urine only if you measured it.
Measurement units
kg
kg
hours
min
mL
mL
Your session estimate
Enter positive pre-run mass, post-run mass, and duration. If the result is not positive, review your measurements before using it.
How the estimate works
Short-term mass loss is used as a field estimate of fluid loss. The calculator adds fluid consumed and subtracts measured urine, then divides by session duration. One kilogram of mass change is treated as approximately one litre for this estimate.