Sauna temperature and humidity

Typical temperatures

Temperatures from Cleveland Clinic. There's no right temperature: start low, and turn it up a few degrees at a time. On a new heater, it takes a few sessions to learn where you like the thermostat.

Humidity and steam

A traditional sauna's air is dry until you ladle water onto the stones. The burst of steam, löyly in Finnish, raises the humidity for a minute or two, which makes the room feel much hotter because sweat can't evaporate as easily. That's why a hot sauna with lots of steam can feel harsh, while the same sauna with a single ladle feels soft.

• Hotter sauna, less water. Above about 85°C, a ladle at a time is plenty.
• Cooler sauna, more steam. At 65 to 75°C, you can add more water for a softer, more humid heat.
• Use clean tap water. Don't use chlorinated pool water or seawater, and only add essential oils made for saunas, diluted, as the heater's manual allows.

The rule of 200

The rule says the temperature in Fahrenheit plus the relative humidity in per cent should add up to about 200. It comes from North American sauna retailers rather than Finnish tradition, and there's no agreed Celsius version, so here are its combinations converted:

Treat it as a starting point, not a limit. Finnish bathers often go over it briefly when they throw water, and it doesn't really apply to infrared cabins, which have no steam.

Measuring it

The controller shows the temperature at its sensor, which is usually near the ceiling. A sauna thermometer and hygrometer on the wall, at head height above the top bench, tells you what you're actually sitting in. Expect the lower bench to be noticeably cooler.