06 · Calculators
Sweat rate calculator
Two trips to the scale and one run in between. Out comes your sweat rate, the fluid you actually lost, and how much of it your gut can realistically take back per hour.
2.0lb
Weight lost
32oz
Fluid sweat out
32.0oz/hr
Sweat rate
32oz/hr
Drink target
The scale only tells you half
Weighing yourself gives you volume, not what was in it. Two runners can drop the same two pounds and one loses 500 mg of sodium while the other loses 2,000 — and the scale cannot tell you which one you are. That number needs an actual test. Read what the sweat test actually measures or find a test near you.
For a clean number: weigh yourself stripped down and toweled dry, before and after, with no drinking and no bathroom stops in between — if you drink during the run, the scale undercounts what you sweat. A pound of weight lost is about 16 fl oz of fluid. The drink target caps at 32 oz an hour because that is near the top of what most guts absorb on the run. Not medical advice.
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