Sweat Rate Calculator
Fluid loss per hour from pre/post exercise weights
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Working out fluid loss per hour from pre/post exercise weights is easier with Sweat Rate Calculator, which answers as you type. Enter Pre-exercise Weight (kg), Post-exercise Weight (kg) and Duration (minutes) in any order — Sweat Rate recalculates on every edit. Sweat Rate ties each output to its formula. Sweat Rate suits budgeting and planning checks. Nothing typed into Sweat Rate leaves your device or the tab. Sweat Rate sits in the Fitness & Exercise section next to free online sweat rate calculator and sweat rate calculator hydration fluid loss exercise weight change. Run Sweat Rate twice to find the driving input. Open Sweat Rate and enter your numbers.
How much fluid do I lose when I train?
Sweat rate is the fluid you lose per hour of exercise. It is estimated by weighing yourself before and after a session and adding back what you drank, then dividing by the time you trained. Enter those figures and the page returns the hourly rate and the fluid to replace.
The 1.4 kg drop is treated as 1.4 litres of fluid, spread over 1.5 hours.
The calculation
Fluid lost (L) = pre weight − post weight (kg)
Sweat rate (L/h) = fluid lost ÷ hours
1.4 kg ÷ 1.5 h = 0.93 L/h. One kilogram of body mass lost during exercise is close to one litre of sweat, because sweat is mostly water.
Worked examples
1.4 kg over 1.5 h → 0.93 L/h
1.0 kg over 1 h → 1.00 L/h
2.0 kg over 2 h → 1.00 L/h
0.8 kg over 45 min → 1.07 L/h
1.5 kg over 2 h → 0.75 L/h
2.4 kg over 1 h → 2.40 L/h (a heavy, hot session)
Why weighing beats guessing
Sweat rates vary enormously — 0.5 L/h for a cool-weather walk and over 2 L/h for hard work in heat — and the same person can sit at both ends of that range in one week. Thirst is a poor guide during exercise because it lags behind losses, and it is blunted further by intense effort. Two weigh-ins, one before and one after, turn a guess into a number you can plan around.
Using the number
- Replace more than you lost. Drinking about 1.25 to 1.5 times the measured loss over the following hours accounts for ongoing urine losses.
- Sodium matters. Salty sweat and white marks on kit suggest a higher sodium loss; plain water alone can dilute blood sodium over long sessions.
- Weigh dry. Wet clothing and a full bladder both distort the figure, so towel off and weigh in similar clothing both times.
- Heat changes everything. The same session in summer can double the rate once you are acclimatised — acclimatisation increases sweat output, not reduces it.
- Losing weight is not the goal. A large drop is a fluid deficit to correct, not a training result, and it impairs the next session.
Re-measure in different conditions, since a single session in one temperature gives one point rather than your range.
Frequently Asked Questions
How do I calculate my sweat rate?
Weigh yourself before and after exercise, subtract the second weight from the first, and divide the difference in kilograms by the hours trained.
Does 1 kg of weight loss mean 1 litre of sweat?
Approximately, yes. Sweat is mostly water, so a kilogram on the scale is close to a litre of fluid, minus anything drunk during the session.
How much should I drink after training?
About 1.25 to 1.5 times the measured loss, sipped over the next few hours — 1.4 kg lost means roughly 1.8 to 2.1 litres.
What is a normal sweat rate?
Most people fall between 0.5 and 2.0 litres an hour, with the higher end in heat and during intense work.
Should I include what I drank during the session?
Ideally yes. Add the volume drunk to the weight difference, since that fluid never shows up as a loss on the scale.
Why is my sweat rate higher in summer?
Heat acclimatisation raises sweat output so the body can cool more effectively. It is an adaptation, not a sign of poor fitness.
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