Sweat Rate Calculator
Calculate your individual sweat rate to determine proper hydration and electrolyte needs during training and racing.
How do you calculate your sweat rate?
Your sweat rate is pre-exercise weight minus post-exercise weight, plus any fluid consumed, divided by hours of exercise. A 1 kg weight loss equals roughly 1 litre of sweat. Most triathletes sweat 500–1500 ml per hour, with heavy sweaters pushing past 2000 ml/hr in heat.
- Weigh yourself naked before and after a 60–90 min session
- Measure all fluid consumed during the session in ml
- Repeat in heat, cool weather and race-pace conditions
- Aim to replace 70–80% of sweat loss during exercise — not 100%
Input Data
Results
Enter your data and calculate to see results
For Best Results
- •Perform this test during a workout that simulates race conditions
- •Repeat the test in different temperatures to understand how your sweat rate varies
- •Account for urination by weighing before and after bathroom breaks
Example calculation
Athlete: 75 kg triathlete, 90 min run in 24°C, drank 600 ml during.
Post-weight: 73.8 kg (lost 1.2 kg).
Total sweat loss: 1,200 ml (weight loss) + 600 ml (fluid in) = 1,800 ml.
Sweat rate: 1,800 ml ÷ 1.5 h = 1,200 ml/hr.
Replacement target: 70–80% = 840–960 ml/hr during racing.
Common mistakes
- Weighing in kit — wet kit can skew the number by 300+ grams
- Not tracking fluid in during the session — this is half the equation
- Running the test once in cool weather and using the number for hot races
- Replacing 100% of sweat rate during the race — causes GI distress and slowing
How this calculator works
Sweat rate = (pre-exercise weight − post-exercise weight + fluid consumed) ÷ duration. Sodium loss is estimated using an average sweat sodium concentration of 1000 mg/L.
Assumptions
- • 1 kg of body-weight loss equals 1 L of sweat
- • Average sweat sodium concentration of 1000 mg/L
- • Single-session estimate — varies with heat, humidity, and acclimatisation
Limitations
- • Real sweat sodium varies 200–2000 mg/L between individuals
- • Does not account for urination during exercise
- • Best repeated across multiple sessions and conditions
Who this is for
- • Triathletes planning hydration for training and racing
- • Heavy sweaters trying to dial in electrolyte intake
- • Anyone preparing for a hot-weather event
Who this is not for
- • Children and adolescents — different fluid needs
- • Athletes with diagnosed hyponatremia history (work with a sports doctor)
Sweat Rate Calculator FAQ
Scientific References
Comprehensive review of sweat rate measurement methods and variables
Official position on nutrition and athletic performance
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