Hydration Tool
Sweat Rate Calculator
Built for runners and cyclists — turn weigh-in data into an hourly sweat rate, dehydration gauge, and next-session hydration target.
What Is Sweat Rate?
Sweat rate measures how much fluid you lose per hour during exercise. It is one of the most practical field tools runners, cyclists, and triathletes use to plan hydration — without needing a lab.
The basic idea:
Total fluid loss = (pre-workout weight − post-workout weight) + fluids consumed
Sweat rate = total fluid loss ÷ workout hours
Because 1 kg of body weight ≈ 1 liter of water, weight loss converts directly into fluid volume.
How to measure it accurately
- Weigh yourself dry before exercise (after bathroom, minimal clothing).
- Track every drink during the session (oz or ml).
- Weigh yourself again immediately after finishing — before showering or eating.
- Record duration in minutes.
Repeat in similar weather and intensity to build a personal baseline.
Reading your results
| Body-weight loss | Typical interpretation | | --- | --- | | < 1% | Generally manageable for most sessions | | 1–2% | Moderate deficit — plan structured rehydration | | 2%+ | High deficit — prioritize fluids + electrolytes |
These are training-planning thresholds, not medical cutoffs.
Water vs. electrolytes
Plain water replaces volume. Electrolytes (especially sodium) help retain fluid and support nerve and muscle function during long or hot sessions.
When sweat rate or dehydration estimates are high, consider:
- Sports drinks with sodium
- Electrolyte tablets or powders
- Salty foods plus fluids after long workouts
This tool provides educational estimates — not medical advice.