Sweat rate calculator, Yousuli Help

What it does

The sweat rate calculator returns your fluid loss per hour from a controlled weighed test, plus a sweat-rate-band estimate of sodium loss per hour (low / average / high based on the typical range for athletes at your sweat rate). It also returns the percentage of body weight lost during the session.

URL: /calculators/ then open Sweat rate. Direct path: /static/calculators/sweat_rate_calculator.html.

Inputs the form asks for

Unit toggle — metric (kg / litres) or imperial (lb / oz).
Weight before test — default 80 kg.
Duration of workout (hours, decimal) — default 2.0. Decimals are fine (1.5 = 90 min).
Quantity of fluid intake (litres in metric, oz in imperial) — default 2.0.
Weight after test — default 74 kg.
Sport (select) — used for the sodium-band lookup since cycling vs running sweat compositions differ slightly.

Run the test in the conditions you race in — temperature, humidity, intensity all change sweat rate. A cool indoor test won't predict a hot outdoor race.

Outputs

Fluid loss per hour (mL/h in metric, oz/h in imperial).
Sodium loss per hour — low / average / high estimates based on the sweat-rate band for your sport.
Sweat rate category — a label for your band (e.g. "high sweater") used by other calculators like the race-day fueling calculator.
Percent body weight lost during the session — over 2% is a flag.

There is no sodium-input field. Sodium loss is estimated from the sweat-rate band, not measured. If you have a real sweat sodium test result, plug it into the fueling calculator's "Sweat Sodium" field rather than this one.

How to run a test

The Sweat Rate Test assessment documents the canonical protocol:

Empty bladder, weigh nude before workout.
Train at goal race intensity for at least 60 minutes.
Track every mL/oz of fluid you drink during the session.
Towel off thoroughly and weigh nude after.

The math: (weight_before - weight_after + fluid_intake) / duration = sweat rate.

Common gotchas

Bladder not emptied. A full bladder before vs empty after shifts the result by 200-400 mL.
Sweat-soaked clothes weighed in. Weigh nude or weigh clothes separately.
Fluid intake not tracked accurately. Sip-counting on the bike during a 2-hour test is unreliable; pre-measure the bottle volume.
Wrong intensity. Sweat rate scales steeply with effort. A test at endurance pace doesn't predict race pace.

When to retest

Every 4-8 weeks during a build phase if conditions vary.
When the race climate is significantly different from where you train (e.g. spring training in cool, race in heat).
After acclimatisation blocks.

Sweat rate calculator