Free tool
Hydration & Sweat Rate Calculator
Cyclists sweat 0.5–2 litres an hour — more in a highveld summer. The goal isn't "drink as much as possible": it's keeping body-mass loss under ~2% without over-drinking.
Your ride
Optional: measure your actual sweat rate (recommended)
Weigh yourself (minimal clothing) before and after a typical 1–2 hour ride, and note how much you drank.
⚠️ Over-drinking is as dangerous as dehydration. Drinking far beyond your sweat rate —
especially plain water on long, slow events — dilutes blood sodium (exercise-associated hyponatremia:
headache, nausea, confusion, and in severe cases seizures). If you gain weight during a ride,
you drank too much. Drink to your plan, not to fear.
The fine print. Guidance follows ACSM fluid-replacement principles: pre-ride
5–7 ml/kg about 4 h out; during, typically 400–1,000 ml/h aiming to keep body-mass loss under ~2%;
after, replace ~125–150% of the deficit with sodium. Sweat rates and sodium losses vary hugely between
riders — the weigh-in test beats any generic number. General guidance for healthy adult
riders; not medical advice.
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