Corrected balance
Intake and urine are handled in the right direction.
Sweat Rate Calculator
Condition-specific sweat rate
Enter your values, then calculate to see a verified result.
Reference range
How this result is calculated
A clear calculation path based on your inputs.
Inputs usedReview the information used for this result.
Full calculation and sourcesOpen Full calculation and sources to audit the inputs, formula sequence, assumptions, and source scope.
Versioned calculationFormula v1.0.0
Condition specific
The result names the test context.
No overdrink prompt
Observed loss is not misrepresented as a mandate.
Weigh beforeUse dry, consistent conditions.
70.0 kgTrack fluidsRecord intake and urine.
500 mL in, 0 mL urineWeigh afterDry off and remeasure.
69.2 kgInterpretation
The method estimates whole-body sweat loss.
Conditions can change the result.
Too much fluid can also create risk.
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Public verification recordFormula v1.0.0
- Review scope
- Metric And US-unit Normalization, Fluid-balance Signs, Duration Scaling, Percentage Change, Zero/negative Boundary Handling.
- Review team
- CalculatorGeek Expert Review Team
- Verified
- 2026-09-27
- Next source review
- 2027-03-27
- Automated fixtures
- 5 cases
Review method
Recompute against the CDC/GSSI field equation; test intake and urine directions, one-hour identity, multi-hour scaling, and equivalent units.
Known limitations
- Field body-mass balance is an estimate and depends on scale and protocol quality.
- Food, metabolic mass loss, respiratory water, stool, and sweat trapped in clothing can bias results.
- Sweat rate changes with environment, intensity, clothing, acclimatization, and fitness.
- Replacing every measured milliliter during exercise is not automatically appropriate.
- Overdrinking can contribute to exercise-associated hyponatremia; individualized guidance may be needed.
Primary sources
- CDC - Sweat Rate Calculation
- Gatorade Sports Science Institute - Hydration Assessment
- U.S. Navy Fitness - estimating sweat losses and rates
Latest update
2026-09-27 ยท Added source-backed endurance calculation, premium result detail, public fixtures, and unified contextual navigation.
Published calculation checks
| Case | Inputs | Expected result |
|---|---|---|
| One-hour test | pre_weight_kg=70 kg, post_weight_kg=69.2 kg, fluid_intake_ml=500 ml, urine_output_ml=0 ml, exercise_minutes=60 min | sweat_loss_liters=1.3, sweat_rate_lph=1.3 |
| Ninety minutes with urine | pre_weight_kg=80 kg, post_weight_kg=79 kg, fluid_intake_ml=750 ml, urine_output_ml=250 ml, exercise_minutes=90 min | sweat_loss_liters=1.5, sweat_rate_lph=1 |
| US-unit equivalence | pre_weight_kg=154.323584 lb, post_weight_kg=152.559886 lb, fluid_intake_ml=16.907 floz, urine_output_ml=0 floz, exercise_minutes=1 hr | sweat_loss_liters=1.3 |
| No scale change with intake | pre_weight_kg=65 kg, post_weight_kg=65 kg, fluid_intake_ml=600 ml, urine_output_ml=100 ml, exercise_minutes=120 min | sweat_loss_liters=0.5, sweat_rate_lph=0.25 |
On this page
Direct answer
The sweat rate calculator corrects pre-to-post body-mass change for fluid consumed and urine passed, then divides estimated sweat loss by exercise duration.
Because sweat rate changes with temperature, humidity, clothing, intensity, acclimatization, and the athlete, one test describes one set of conditions rather than a permanent personal constant.
Use the measured rate when reviewing reminders in the Running Race Planner, and keep fueling arithmetic separate with the Carb Loading Calculator.
How to use the calculator
- Measure dry pre-exercise body mass.
- Track every drink and any urine output.
- Dry off and measure post-exercise body mass consistently.
- Enter actual elapsed duration.
- Repeat under other representative conditions before planning.
Inputs, outputs, and result meaning
Inputs
- Pre-exercise body mass: Measure with minimal dry clothing and a consistent scale.
- Post-exercise body mass: Dry off and use comparable clothing and scale conditions.
- Fluid consumed: Include all drinks consumed during the test.
- Urine output: Enter urine passed during the test; use zero when none.
- Exercise duration: Use the actual elapsed duration of the test.
Outputs
- Estimated sweat loss: Scale loss plus fluid consumed minus urine output.
- Sweat rate: Estimated sweat loss divided by exercise hours.
- Scale body-mass change: Pre-exercise minus post-exercise scale reading.
- Body-mass change: Scale change as a percentage of pre-exercise mass.
- Observed loss per 15 minutes: One quarter of the observed hourly sweat rate, not a drinking prescription.
Formula and methodology
Sweat loss: pre-exercise mass - post-exercise mass + fluid consumed - urine output. Kilograms of acute mass change are approximated as liters of water.
Sweat rate: sweat loss divided by exercise duration in hours.
Food, respiratory water, substrate oxidation, stool, and sweat retained in clothing can affect a field estimate. Consistent protocol matters more than false decimal precision.
Worked examples
One-hour run
70.0 kg before, 69.2 kg after, and 0.5 L consumed gives 0.8 + 0.5 = 1.3 L estimated sweat loss, or 1.3 L/h.
Ninety minutes with urine
1.0 kg scale loss + 0.75 L intake - 0.25 L urine = 1.5 L. Divide by 1.5 hours for 1.0 L/h.
Interpretation and limitations
- Field body-mass balance is an estimate and depends on scale and protocol quality.
- Food, metabolic mass loss, respiratory water, stool, and sweat trapped in clothing can bias results.
- Sweat rate changes with environment, intensity, clothing, acclimatization, and fitness.
- Replacing every measured milliliter during exercise is not automatically appropriate.
- Overdrinking can contribute to exercise-associated hyponatremia; individualized guidance may be needed.
Frequently asked questions
Why add fluid consumed?
Without adding it back, drinking during the test would hide part of the sweat loss.
Why subtract urine?
Urine is measured fluid loss but is not sweat, so it is removed from the sweat estimate.
Can I use one test for every race?
No. Repeat the protocol in representative weather, intensity, clothing, and acclimatization states.
Should I drink exactly my sweat rate?
Not automatically. Replacement depends on duration, access, tolerance, thirst, sodium context, and risk of both under- and overdrinking.
Why did the calculator reject a negative result?
A negative sweat loss usually indicates inconsistent weights or missing intake/output data and should be checked rather than displayed as physiology.
Sources and transparency
- CDC - Sweat Rate Calculation
- Gatorade Sports Science Institute - Hydration Assessment
- U.S. Navy Fitness - estimating sweat losses and rates
CalculatorGeek independently recomputed the public fixtures on 2026-09-27. Sources establish the method or its safe interpretation; they do not make a field estimate equivalent to laboratory measurement or individualized professional advice.