Sweat Rate Calculator
Weigh yourself before and after a workout, add what you drank, and get your sweat rate in liters per hour.
- Free
- No sign-up
- Runs in your browser
- Shows the math
Enter both weights and your time to see your sweat rate.
(Weight before − weight after) + drink − urine, divided by hours
General information, not medical advice. Medical disclaimer
How to run the test
- Weigh yourself before. Use an accurate scale and urinate first if you need to. The Korey Stringer Institute handout says to wear the same clothing for both weigh-ins.
- Exercise for a measured time. One hour is the easiest. The handout says 30 minutes also works.
- Measure what you drink. Use a bottle with markings, or know the size of your bottle.
- Skip the bathroom if you can. If you do urinate, enter the amount in the optional field.
- Towel off and weigh again. Put both weights in the calculator.
Worked example: 160 lb to 158 lb in 60 minutes
- 160 lb − 158 lb = 2 lb. That's 0.91 kg (2 divided by 2.2046), so about 907 mL.
- You drank 16.9 fl oz, which is 500 mL.
- 907 + 500 = 1,407 mL of sweat, which rounds to 1,410 mL.
- 60 minutes is 1 hour, so the rate is 1.41 liters per hour (48 fl oz).
- You ended 1.3% lighter than you started, which is under the 2% line in the ACSM position stand.
Press “Try an example” above to load it.
What the math assumes
Weight lost on the scale is treated as sweat, with one kilogram counted as one liter. That's our simplification. The sources listed below use the change in body mass the same way (Godek and colleagues report sweat rate in liters per hour from the change in body mass, adjusted for fluids consumed and urine produced), but none of them spells out the conversion. Results are rounded to the nearest 10 mL.
The test also misses small things: sweat that stays in your clothes, water lost through breathing, and the weight of food or a bathroom trip. Treat the answer as an estimate for that session, in those conditions.
What published sweat rates look like
The American College of Sports Medicine position stand says there's considerable variability in sweating rates between individuals, which is why it recommends customized fluid plans. One study shows how high the numbers can run in heat. It followed 15 athletes practicing in a hot, humid environment and found average sweat rates of 2.14 liters per hour in American football players and 1.77 in cross country runners.
Those are athletes in hot conditions, not a normal range for everyone. If you walk or jog easily in mild weather, expect a lower figure, and calculate it again in different weather. The Korey Stringer Institute handout notes that men and highly fit people generally have higher sweat rates.
What to do with your number
The ACSM position stand says the goal of drinking during exercise is to prevent excessive dehydration, defined there as more than 2% body weight loss from water deficit. The calculator flags sessions that go past that.
It doesn't turn your sweat rate into a drinking order. Drinking more than you lose is the risk: the 2015 consensus statement on exercise-associated hyponatremia says excess fluid intake underlies all known fatal cases, and it calls drinking when you're thirsty the safest individualized strategy. Our reading: use the number to understand your losses and to plan around hot days, and don't force fluid to hit it. For daily targets use the Daily Water Intake Calculator, and read how much water is too much before you push your intake up.
When this number does not apply
- You're pregnant or breastfeeding.
- You have a kidney, heart or liver condition.
- You have been given a fluid limit or a specific drinking target.
- You take a medication that affects fluids or sodium.
- This is for a child or teen. The calculator is for adults.
Related
Frequently asked questions
How do you calculate sweat rate?
Weigh yourself before and after exercise, add the fluid you drank, subtract any urine, and divide by the hours you exercised. In kilograms and milliliters: (weight before − weight after) × 1,000 + drink − urine, divided by hours. The method matches the one the American College of Sports Medicine describes: estimate sweat rate by measuring body weight before and after exercise.
How long should the test be?
The Korey Stringer Institute handout says one hour is easiest, and that 30 minutes works if you double the result to get an hourly rate. This calculator accepts anything from 30 to 480 minutes and does the per-hour math for you. Very short tests make the hourly number swing a lot.
Does it matter what I wear?
Yes. The Korey Stringer Institute handout says to weigh in exactly the same clothing both times, on an accurate scale. Our tip: towel off before the second weigh-in, since sweat left on you or your clothes adds weight.
What is a normal sweat rate?
We didn't find a published normal range for everyday exercisers, so we don't give one. The American College of Sports Medicine says sweating rates vary a lot between individuals. For scale, one study of 15 athletes practicing in a hot, humid environment measured an average of 1.77 liters per hour in cross country runners and 2.14 in American football players.
Should I drink my sweat rate during exercise?
Not as a rule. Your sweat rate is how much you lost. Matching it would keep your weight flat, but the 2015 consensus statement on exercise-associated hyponatremia says drinking when thirsty is the safest individualized strategy, and that excess fluid intake underlies all known fatal cases. Use the number to understand your losses, and talk to a clinician or sports dietitian before building a drinking plan around it.
Why does my sweat rate change from day to day?
Conditions change it. The Korey Stringer Institute handout says to calculate it separately for different environments, such as winter and summer, and that sweat rates generally rise after 10 to 14 days of heat exposure.
Does this tell me how much sodium I lose?
No. The American College of Sports Medicine position stand says the amount of electrolytes in sweat also varies a lot between people. This calculator measures fluid only. Our guide on electrolytes covers when they matter.
Sources
- Sawka MN, Burke LM, Eichner ER, Maughan RJ, Montain SJ, Stachenfeld NS. American College of Sports Medicine position stand. Exercise and fluid replacement. Medicine & Science in Sports & Exercise 39(2):377-390. PubMed 17277604.
- Godek SF, Bartolozzi AR, Godek JJ. Sweat rate and fluid turnover in American football players compared with runners in a hot and humid environment. British Journal of Sports Medicine 39(4):205-211, 2005. PubMed 15793087, DOI 10.1136/bjsm.2004.011767.
- Korey Stringer Institute, University of Connecticut. Sweat Rate Calculator (handout).
- Hew-Butler T, Rosner MH, Fowkes-Godek S, et al. Statement of the 3rd International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015. British Journal of Sports Medicine 49(22):1432-1446. PubMed 26227507, DOI 10.1136/bjsports-2015-095004.
How this page was built. The sweat rate calculator on Daily Water Calculator was built by Cedrick Reese. The method was checked against three sources: the ACSM position stand abstract, the Godek 2005 study abstract, and the Korey Stringer Institute handout. The formula was tested in code against hand-worked examples, including the one on this page. The one-kilogram-equals-one-liter step is our own simplification and the page says so. We recheck the sources when we update the page. Last reviewed: .
General information for healthy adults, not medical advice. If you are pregnant or breastfeeding, or you have kidney, heart or liver conditions or a fluid limit, ask a clinician first. Terms and medical disclaimer.