Tools › Sweat rate calculator
General fitnessWeigh yourself before and after a session to find how much you sweat per hour. Runs in your browser; nothing is saved or sent.
Pee just before you weigh in, and weigh again before you use the bathroom afterwards, so urine doesn’t count toward your weight change.
The American College of Sports Medicine (ACSM) position stand on fluid replacement (2007) says individual sweat rates can be estimated by weighing yourself before and after exercise, and recommends avoiding losses of more than 2% of body weight to dehydration. A newer expert panel (Belval et al., 2019, convened with sponsor support from Gatorade) describes the same method, puts the line at 2–3%, and warns against drinking more than you sweat. The calculation: sweat lost = weight before − weight after + what you drank, treating 1 kg of sweat as about 1 liter (our simplification). The newer panel says to account for any urine passed; peeing before the first weigh-in and weighing again before the bathroom afterwards keeps that at zero. If you had to go during the session, your result will read a little high. Sweat rates vary between people, so your number applies to the conditions you measured it in; repeat it when the conditions change. The weigh-in method is reliable for most sessions under about 2–3 hours (Belval et al., 2019). Our cycling guide walks through it.
General information for healthy adult athletes, not medical advice. If you have a medical condition, are pregnant, or have a history of disordered eating, talk to a doctor or registered dietitian before changing how you eat.