๐ฆ Sweat Rate Calculator
Sweat loss (L) = (pre-exercise weight โ post-exercise weight) + fluid intake โ urine loss, divided by duration.
Enter your body weight before and after exercise, fluid intake and urine loss during exercise, and the exercise duration to calculate your hourly sweat rate, using the mass-balance formula used in sports science (ACSM).
How to use
- Enter your body weight before exercise (kg).
- Enter your body weight after exercise (kg).
- Enter the fluid you drank (L) and urine you produced (L) during exercise.
- Enter the exercise duration (hours).
- Your hourly sweat rate is calculated automatically.
How the calculation works
This tool calculates how much you sweat per hour (sweat rate) from the change in body weight before and after exercise. Sweat loss (L) = (weight before โ weight after) (kg) + fluid drunk during exercise (L) โ urine passed during exercise (L) Sweat rate (L/h) = sweat loss รท exercise duration (h) Over a short session, weight lost is almost all water, and 1 kg of water is about 1 L. Fluid drunk during exercise added to your weight, so it is added back; urine is not sweat, so it is subtracted. Knowing your sweat rate tells you roughly how much to drink per hour while exercising. The American College of Sports Medicine recommends keeping weight loss from exercise below 2% of body weight.
Worked example
70.0 kg before, 69.2 kg after, 0.5 L drunk, 0.1 L urine, 1 hour Sweat loss: (70.0 โ 69.2) + 0.5 โ 0.1 = 1.2 L Sweat rate: 1.2 L/h Weight loss is 0.8 รท 70 โ 1.1%, within the 2% guideline.
Things to be aware of
- Weigh yourself in the same clothing before and after (ideally after towelling off). Sweat-soaked clothes make sweat loss look smaller.
- Sweat rate changes a lot with temperature, humidity, intensity and heat acclimatisation, so re-measure each season.
- Drinking far more than you sweat can dilute blood sodium (hyponatraemia). Replace salt as well during long sessions.
FAQ
What's the formula?
Fluid loss from sweat (L) = (pre-exercise weight โ post-exercise weight) (kg, converted roughly 1kg โ 1L of water) + fluid intake (L) โ urine loss (L), then divided by exercise duration (hours) to get the hourly rate. This mass-balance approach is widely used in sports science.
What's a typical sweat rate?
It varies widely with exercise intensity, temperature, and body size, but a common range for general exercise is roughly 0.5-2 L per hour.
What's this useful for?
It helps you gauge how much fluid you need to replace during exercise โ especially useful for endurance sports or exercising in hot conditions, to help plan hydration and avoid dehydration.