Sweat rate and hydration calculator
Work out your sweat rate per hour from a weigh-in either side of training, see how much bodyweight you lost, and get the drinking and sodium plan that keeps you inside the 2% where performance drops. Free.
The method: sweat lost = (weight before − weight after) + everything you drank. Weigh yourself in the same, dry kit both times.
Example: 80 kg down to 78.6 kg over an hour, 500 ml drunk
- Sweat lost: 1.9 L
- Sweat rate: 1.9 L/h
- Bodyweight lost: 1.75%: Mild dehydration
- Sodium lost: 1520 mg
- Drink during a session like this: 0.3 L/h
1–2% lost. Fine for a short session, and worth drinking more in a long or hot one.
Sweat rate rises with heat and intensity, so test this in conditions like the ones you will race in. A race hall in October is not your garage in July.