Free tool · fluid & electrolytes
Sweat rate calculator
Weigh yourself before and after training once – and you know how much you sweat per hour, how much sodium you lose and how much to drink next time.
- ACSM method
- Sodium range after Baker 2017
- Drinking plan for next session
- No sign-up
- body mass loss limit
- 2 %
- mmol sodium per litre of sweat
- 10–90
- no sign-up
- €0
Your measurement
How to measure: weigh yourself naked or in dry underwear before the session; afterwards towel off and weigh again the same way. Count what you drank.
Sweat rate
1.04L per hour
Total fluid loss
1.30 L
Body mass change
-1.0 %
Under 2 % body mass loss – within ACSM guidance.
Estimated sodium loss
600–1790 mg
≈ 480–1430 mg per hour
Sweat contains 10–90 mmol sodium per litre depending on the person. The calculator uses 20–60 mmol/L – only a sweat test is more precise.
For your next session
- Your fluid intake fits – keep it at the same effort.
- Afterwards: drink 1000–1200 ml over the next hours (125–150 % of the deficit), ideally with a little salt or a salty meal.
- For sessions over 60–90 minutes the ACSM recommends drinks with 20–30 mmol sodium per litre (460–690 mg/L).
Electrolytes from the shop
Our products are potassium-rich mineral drinks low in sodium – they don't replace a salty sports drink in very long sessions.
A calculation aid, not a diagnosis. With high blood pressure, heart or kidney disease, agree fluid and salt with your doctor. Everything runs only in your browser.
Method
How the sweat rate calculator works
- 1
Sweat rate
Weight before minus weight after plus fluid drunk minus urine, divided by duration. 1 kg of weight loss is about 1 litre of fluid.
- 2
Body mass loss
Under 2 % of body weight is uncritical. Beyond that, endurance performance can suffer, especially in heat. A gain means you drank too much.
- 3
Sodium loss
Sweat contains 10–90 mmol sodium per litre, on average around 40. The calculator shows a range (20–60 mmol/L, 60–80 mmol/L for salty sweat).
- 4
Drinking plan
Fluid per hour to keep the loss under 2 % at the same effort, and 125–150 % of the deficit afterwards.
Sweat loss FAQ
How do I measure my sweat rate?
Weigh yourself naked or in dry underwear before training, towel off afterwards and weigh again the same way. Add what you drank, subtract toilet breaks and divide by the duration.
How much sweat is normal?
Most athletes lose 0.5 to 2 litres per hour – depending on intensity, temperature, clothing and individual factors. That's why measuring yourself is worthwhile.
Do I need electrolytes?
For sessions up to about 60 minutes water is usually enough. For long sessions, heat or salty sweat the ACSM recommends drinks with 20–30 mmol sodium per litre.
Can you drink too much?
Yes. Drinking more than you sweat during long efforts risks dangerously low sodium (hyponatraemia). Gaining weight during training is a warning sign.