How the sweat rate calculator works
Why the weigh-in beats every formula
Sweat rate ranges from 0.5 to 2.5+ liters per hour across people and conditions — a spread no formula captures. The weigh-in test measures YOUR rate under YOUR conditions: (weight lost × 16 oz) + fluids in − urine out, divided by hours. It requires a scale and one honest session; it outperforms every estimate on this site.
Reading your number
Under 20 oz/hr is typical for easy efforts in mild conditions; 30–50 oz/hr is common in heat or hard efforts; 60+ happens in elite hot-weather work and is hard to replace fully. Practical absorption caps (~28–48 oz/hr for most guts) matter: if your rate exceeds your absorption, pre-hydration and cooling strategies join the plan.
The rehydration arithmetic
Replace 150% of losses over the following hours — the extra 50% covers inevitable urine output. Sodium helps the retention (plain water plus a salty meal works fine; commercial electrolytes work too). A 2-lb loss = 32 oz of sweat = 48 oz of rehydration, spread out, with food.