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NUTRITION & PHYSIOLOGY

Sweat Rate
Calculator v1.0

Estimate your hourly sweat rate by comparing pre- and post-exercise body weight, accounting for fluid intake during the session. Use the results to plan your hydration strategy for training and racing.

Inputs
kg
kg
ml
min
hr
Results
Sweat Rate
1,300 ml/hr
hourly fluid loss
Total fluid lost 1,300 ml
Body weight lost 1.14%
Dehydration status Mild dehydration
Aim to drink 1,000 ml/hr (250 ml every 15 minutes) over a 3-hour session.
% Body Weight Lost Status
< 1%Well hydrated
1 – 2%Mild dehydration
2 – 3%Moderate dehydration
3 – 4%Significant dehydration
> 4%Severe dehydration
Methodology

Total fluid lost = (Pre-weight − Post-weight) × 1000 + Fluid consumed
Sweat rate = Total fluid lost ÷ (Duration ÷ 60)
% Body weight lost = (Pre-weight − Post-weight) ÷ Pre-weight × 100

Weight change is assumed to represent fluid loss only. For best accuracy, weigh yourself nude or in dry clothing before and after exercise, and account for any urination during the session. Drink rate = Sweat rate − (2% of pre-weight ÷ planned hours), at most 1,000 ml/hr and never more than your sweat rate. This keeps body-mass loss under 2% over the session (ACSM 2007 position stand, doi:10.1249/mss.0b013e31802ca597). The 1,000 ml/hr cap is our own value. The same rule sets fluid in the race fuelling planner. The 15-minute figure divides the hourly drink rate into four equal portions.
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Changelog: v1.1 — Drink advice follows the one fluid rule (loss under 2% of body mass, at most 1.0 L/hr, never above sweat rate) for the session length you enter. It was 100% of sweat rate. v1.0 — Initial release. Pre/post weight to hourly sweat rate, dehydration status, and personalised hydration plan.
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