Sweat Rate Calculator: free fluid loss calculator.
Weigh yourself before and after a session. Get your sweat rate per hour and how much body weight you lost.
Your sweat rate
1 h · mild
Test again in other conditions: sweat rate moves with heat, humidity and effort. Plan your race fuel with this sweat rate →
Hand it to your AI
Your AI can check these numbers against your training and adjust them. The prompt has your results filled in.
See the prompt
I did a sweat test: 1 h in mild conditions. I weighed 75 kg before and 74.2 kg after, drank 500 ml. That works out at a sweat rate of 1.3 l an hour, and I lost 1.1% of my body weight. Remember this sweat rate for my training and racing. Tell me how much to drink per hour in my next long session and on race day so I lose less than 2% of my body weight, and never more than I sweat.
Gemini, Grok Bot, Dots, Muse and Cue: copy the prompt and paste it in.
Your AI could check this against your real training. Join Memory.fit.
On Android now: get it on Google Play. One email when the iPhone app is on the App Store.
How it works
How the Sweat Rate Calculator works.
Almost all the weight you lose during a session is sweat. So the simplest sweat test is two weigh ins: one before, one after, with the fluid you drank added back and any urine taken off. One kilogram lost is treated as one liter of sweat.
Weigh yourself without clothes, dry off first, and do a session of at least 45 minutes at the effort you will race at. Write down everything you drink.
Your sweat rate changes with heat, humidity and effort, and it differs a lot between athletes. So test more than once, in the conditions you race in. Losing more than 2% of your body weight is the line the hydration research uses; above it, performance tends to drop.
The formula
- sweat rate (ml/h) = ((weight before − weight after) × 1,000 + fluid drunk − urine) ÷ hours
- body weight lost (%) = (weight before − weight after) ÷ weight before × 100
The science
Where the numbers come from.
These are the same rules Memory.fit's engine uses when your AI asks it for a number, read from one registry of cited sources.
Sawka MN, Burke LM, Eichner ER, et al. American College of Sports Medicine Position Stand: Exercise and Fluid Replacement (2007). Medicine & Science in Sports & Exercise 39(2):377-390.
Position stand · 2007 · doi:10.1249/mss.0b013e31802ca597
McDermott BP, Anderson SA, Armstrong LE, et al. National Athletic Trainers' Association Position Statement: Fluid Replacement for the Physically Active (2017). Journal of Athletic Training 52(9):877-895.
Position stand · 2017 · doi:10.4085/1062-6050-52.9.02
Baker LB. Sweating Rate and Sweat Sodium Concentration in Athletes: A Review of Methodology and Intra/Interindividual Variability (2017). Sports Medicine 47(Suppl 1):111-128.
Review · 2017 · doi:10.1007/s40279-017-0691-5
Example
A worked example.
A 75 kg runner on a 60 minute tempo run in mild weather.
- 1Before: 75.0 kg. After: 74.2 kg. That is 0.8 kg, or 800 ml.
- 2They drank a 500 ml bottle and didn't pee, so total sweat is 800 + 500 = 1,300 ml.
- 3Over one hour that is a sweat rate of 1.3 liters an hour. They lost 1.1% of their body weight, under the 2% line.
Questions
Sweat Rate Calculator: questions.
Pee, then weigh yourself without clothes. Train for 45 to 90 minutes and note everything you drink. Towel off and weigh yourself again, without clothes, before you drink or pee. Enter the numbers here.
Most athletes sweat somewhere between 0.5 and 2 liters an hour, and some well over that in heat. The spread between people is large, which is why your own number beats any average.
Yes, often by a lot. Test in conditions close to your race, and test again when the season changes.
The hydration position stands use 2% as the line above which endurance performance tends to drop. Drinking to stay under it, and never drinking more than you sweat, is the balance they describe.
Put it into the Race Fuel Planner. It gives you a fluid range per hour that keeps you under 2% and never above your sweat rate.
Not medical advice. These numbers come from published research on groups of athletes. Your own needs can differ; talk to a doctor or a sports dietitian about any health condition.