How it works
sweat (L) = weight before − weight after + fluid drunk; rate = sweat ÷ hours
This page keeps the calculation centered on one relationship: sweat (L) = weight before − weight after + fluid drunk; rate = sweat ÷ hours. Inputs are normalized before the final display, which keeps mile, kilometer, pace, speed, or zone outputs from drifting because of rounding. Use the number as a consistent model output, then layer in terrain, weather, recovery, and race execution. Keep the fixed reference values in view: 70 kg, 69 kg, 0.5, 1, 1.5, 2%.
Sources
- Sweat-rate measurement Sweat loss = (pre-exercise body mass − post-exercise body mass) + fluid ingested; 1 L sweat ≈ 1 kg body mass. Standard field method (e.g. ACSM/NATA hydration guidance).
- 2% dehydration threshold Body-mass losses beyond ~2% are commonly associated with measurable declines in endurance performance and thermoregulation.
- Fluid absorption limits Gastric emptying and intestinal absorption cap practical fluid intake, so very high sweat rates cannot always be fully replaced during exercise.
FAQ
When should I use the sweat rate calculator?
Use it when you want a fast planning number before a run, race, workout, or gear decision. It gives you a consistent estimate without asking you to create an account.
What inputs matter most?
The best result comes from honest, current inputs. Recent race times, realistic body measurements, accurate workout data, and the correct unit setting matter more than perfect formatting. Keep the fixed reference values in view: 1.5, 0.5, 1.
How should I read the result?
Treat the output as a planning reference, not a promise. Use it to compare options, set a target range, or sanity-check your watch data before making the final call. Keep the fixed reference values in view: 0.5, 2.0.
Does this work in miles and kilometers?
Yes. PacerRunning is written for US runners first, so miles are easy to use, but metric conversions are kept alongside them where the tool needs both views. Keep the fixed reference values in view: 2%.
Why might my real-world result differ?
Terrain, wind, heat, sleep, fueling, training fatigue, and measurement error can all move the real outcome away from the estimate. The Sweat Rate sweat rate calculator cannot see those details.
Can beginners use it?
Yes. You do not need advanced training knowledge. Enter the numbers you know, read the result as a guide, and keep your effort comfortable when you are unsure.
Sweat Rate Calculator results are estimates from the entered data and the cited method. They are useful for planning and comparison, but they are not a diagnosis, prescription, guaranteed race result, or substitute for a coach or clinician.