MEASURE NORMAL BEHAVIOUR
Drink normally and measure it. You do not need to withhold fluid. Use dry minimal clothing, the same scale and a representative ride. This tool estimates loss; it does not prescribe how much you must drink or diagnose a hydration problem.
After using the toilet; nude or dry minimal clothing.
Remove wet kit and towel dry before weighing.
Count every bottle, refill and drink.
Use 0 only if there was no bathroom stop.
Quick answer
A cycling sweat-rate test estimates fluid lost during one representative ride. Record dry pre- and post-ride body mass, everything you drink, any urine produced and the duration. The result belongs to those conditions: it is not a universal drinking target and it does not measure sweat sodium.
HOW IT WORKS
Estimated sweat loss equals pre-ride body mass minus post-ride body mass, plus fluid consumed, minus urine produced. One kilogram of acute mass change is treated as roughly one litre of water, then total loss is divided by ride duration in hours. Wet clothing, scale precision, food and unrecorded losses create error, so repeat comparable tests.
- 01
Prepare a representative ride
Choose conditions, clothing and intensity relevant to the event or training question. Use the same reliable scale before and after.
- 02
Measure normal behaviour
Weigh after using the toilet in dry minimal clothing. Drink normally and record every bottle, refill and bathroom stop; do not withhold fluid for the test.
- 03
Enter the four measurements
Add pre- and post-ride body mass in kilograms, fluid consumed and urine in millilitres, and the ride duration.
- 04
Interpret, repeat and audit
Attach temperature, humidity, airflow, clothing and workload to the result. Repeat comparable sessions, avoid drinking enough to gain body mass and do not assume 100% replacement is required.
LIMITATIONS
One field result is noisy and specific to its conditions. Wet clothing, inaccurate scales, food, respiratory water and unrecorded fluid can distort it. The calculator estimates fluid loss only: it cannot measure sweat sodium, diagnose dehydration, prescribe a universal millilitres-per-hour target or decide whether symptoms need treatment.
When to see a coach
Use a qualified sports dietitian or clinician when repeated measurements are extreme, you have recurrent heat illness, confusion, collapse, persistent gastrointestinal problems, kidney or cardiovascular disease, or take medication that affects fluid or sodium balance. Confusion, seizure, collapse, loss of coordination or altered consciousness during or after exercise needs urgent medical help.