How this calculator works
Sitting in heat raises heart rate and body temperature, and the body spends some energy on sweating and thermoregulation. Measured energy use is roughly twice resting metabolism, or about 2 METs, far below even a gentle walk. The estimate here applies 2 METs to body mass and time. Sauna use does not meaningfully increase fat oxidation, and any weight lost during a session is water that returns with food and drink. The numbers are small, and the evidence comes from short studies of healthy adults, so treat the result as an order of magnitude rather than a precise burn.
Formula
kcal/min = 2 x 3.5 x body mass (kg) / 200. Calories = kcal/min x minutes. Calories per hour = kcal/min x 60. Fat equivalent = calories / 7,700.
Worked example
A 70 kg person spends 15 minutes in a sauna: 2 x 3.5 x 70 / 200 = 2.45 kcal/min, or 36.75 kcal. That is 147 kcal an hour and about 0.005 kg of fat equivalent. An 80 kg person for 30 minutes uses 2.8 kcal/min, or 84 kcal, and 168 kcal per hour.
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Frequently asked questions
Can a sauna help me lose weight?
Not in any lasting way through calories. The energy cost is small and the immediate weight change is water. A sauna can feel good and may support recovery, but fat loss needs a sustained energy deficit.
Why do I weigh less after a sauna?
You sweat out water, and the scale reflects that fluid loss. Drinking water restores it. Sauna use can be dangerous if you are dehydrated, have heart problems or have been drinking alcohol.
Is a steam room different?
It is similar in energy cost. Steam rooms feel hotter because of the humidity, but the metabolic rate while sitting is still low. Use the same estimate and treat any difference as small.