Health Calculators
Sweat rate calculator.
Weigh yourself before and after a workout, add the fluid you drank and any urine. Get your sweat rate in litres per hour. Runs in your browser; nothing is sent or stored.
Your workout
Sweat rate
Fill the form and press Calculate sweat rate.
How sweat rate is worked out
Sweat loss = body mass before − (body mass after − fluid drunk + urine passed). It is divided by the exercise time in hours. One gram of body mass lost is taken as about 1 mL of sweat. Fluid and urine are counted in mL. The calculator does not correct for breath, food eaten, stool or sweat trapped in clothing, so it is an estimate.
Worked example. 70.0 kg before, 69.0 kg after, 500 mL drunk, no urine, 60 minutes. Mass lost 1,000 g, so 1,000 + 500 = 1,500 mL of sweat in one hour: 1.5 L/h. Net body mass change is 1.0 kg, which is 1.4% of 70 kg.
Source (opened 2026-10-05): Baker LB (2017), “Sweating Rate and Sweat Sodium Concentration in Athletes: A Review of Methodology and Intra/Interindividual Variability”, Sports Medicine 47(Suppl 1):111–128, PMC5371639. It gives the whole-body sweating rate formula above. The 1 g to 1 mL step is this page's own simplification, not a claim from the review. This page does not set a drinking target or a dehydration limit. For daily fluid needs see the water intake calculator.
FAQ
How do I measure my sweat rate?
Weigh yourself undressed or in light clothes before and after exercise, after urinating and towelling off, and note fluid drunk and urine passed. Enter those numbers and the exercise time.
How much sweat is a lot?
The figure varies widely between people, activities and weather. Compare your own sessions rather than a single norm, and repeat in similar conditions.
Why add the fluid I drank?
Drinking adds weight back, so the scale alone understates sweat loss. The formula adds fluid drunk and takes away urine.
Should I drink back everything I sweat?
This tool does not give a drinking target. Drinking far more than you need can be unsafe, so ask a doctor, dietitian or coach for a plan, especially for long events.
Is 1 g of weight really 1 mL of sweat?
It is this tool's own simplification, treating sweat as water-like in density; the Baker 2017 review does not state it. It also ignores respiratory water loss and metabolic mass loss, which the review puts at roughly 5-15% combined, so the result can overstate true sweat loss, especially in long, intense or cool, dry sessions.
Daily needs: water intake calculator.
Disclaimer
General information, not medical advice. A single sweat test is rough. People with heart, kidney or other conditions, or who take medicines that affect fluid balance, should ask their doctor about fluids and exercise.