Sweat Rate Calculator
Weigh before/after training → individual sweat rate
Good hydration. Keep it up!
Recommended fluid intake next time: ~1267 ml/h
How much you actually sweat
Sweat rates are highly individual: two people can lose double or half as much in the same session. Blanket drinking advice therefore often misses.
Measuring is simple: weigh before, train, weigh after, add what you drank. The calculator turns that into your hourly sweat rate.
How it is calculated
Sweat loss in litres = weight before − weight after + fluid drunk. Sweat rate in ml/h = sweat loss / duration in hours × 1000. Weight loss in % = (weight before − weight after) / weight before × 100.
What you drank is added back because it hides weight loss on the scale: without that step, anyone who drinks a lot would get a sweat rate that is far too low.
Example: 70.0 kg before, 68.8 kg after, 0.7 l drunk, 90 minutes. Sweat loss = 70.0 − 68.8 + 0.7 = 1.9 l. Sweat rate = 1.9 / 1.5 × 1000 = 1267 ml/h. Weight loss = 1.2 / 70.0 × 100 = 1.7 %.
The rating: under 2 % weight loss is fine, 2 to 3 % mild, 3 to 5 % noticeable and above 5 % severe dehydration.
To calculate sweat rate properly, weigh yourself both times without clothes and after using the toilet — a 300 g wet jersey would otherwise add 200 ml/h of error.
What to do with it
Afterwards you know how much to drink per hour in a race — and whether your previous plan was too thin or too generous.
Measure at different temperatures. In summer the rate can be twice the winter figure.
Frequently asked questions
- How precisely do I need to weigh?
- Undressed and towelled dry, before and after, on the same scale. A hundred grams corresponds to roughly a decilitre.
- Should I replace every loss?
- No. Two to three percent weight loss is unproblematic. Drinking more than needed risks a full stomach and, at worst, diluted blood sodium.
- Why is my rate different today?
- Heat, humidity, intensity and acclimatisation all shift it noticeably. A single measurement is a reference point, not a law.