What is the 200 rule for saunas?

The 200 rule for saunas is a general guideline stating that the combined total of the sauna temperature (in °F) and the relative humidity (in percent) should not exceed 200 for a comfortable, safe session.

The 200 rule helps bathers calibrate the balance between heat and moisture — two variables that together determine how oppressive a sauna session actually feels. A traditional Finnish sauna running at 170°F with 30% humidity hits exactly 200, which most experienced users find intense but manageable. An infrared sauna typically operates at lower temperatures (120–150°F) with minimal humidity, so the combined number sits well under 200, making sessions more accessible for people who find high-heat environments difficult to tolerate.

• The 200 rule target: temperature (°F) plus relative humidity (%) should total no more than 200.
• Traditional Finnish sauna example: 170°F + 30% humidity = 200 — at the guideline ceiling.
• Far infrared sauna typical range: 120–150°F with under 20% humidity, producing a combined total of 140–170.
• Exceeding 200 (e.g., 190°F + 40% humidity) increases heat stress risk, particularly for cardiovascular strain.
• The 200 rule applies to conventional and steam saunas; far infrared saunas operate below the threshold by design.