Sweat loss and hydration calculator
Estimate your sweat rate and the amount of fluid to drink to make up for your fluid loss during a workout, based on your weight before and after exercise and the amount you drank during the session. The calculation runs entirely in your browser.
How it works
Weighing yourself before and after exercise is the reference method athletes and fitness coaches use to estimate an individual sweat rate: one kilogram lost during exercise corresponds to roughly one liter of sweat. This tool adds the fluids you drank during the session to that weight loss to get the total volume sweated, then divides it by the duration of the exercise to give a sweat rate in liters per hour.
Why is the recommended rehydration higher than the measured loss?
After exercise, the body keeps losing fluids (residual sweating, urine) before fluid balance is restored. That's why it's generally recommended to drink about 1.5 times the fluid deficit measured, rather than just a liter for every liter lost, to return to a normal hydration state.
Does this estimate replace personalized medical or sports advice?
No. This calculation is an informational estimate based on a simplified method commonly used in athletic training; it does not replace the advice of a doctor, a sports dietitian or a healthcare professional, especially in extreme heat, during prolonged exercise or with a pre-existing health condition.
The calculation runs entirely in your browser: none of the data you enter is sent to a server.