Plan sauna sessions for recovery.
Tolerable sauna time depends on temperature and humidity together, because humidity blocks evaporative cooling — ninety degrees at ten percent humidity is comfortable for a quarter of an hour while the same temperature in a steam room is not. A traditional Finnish session is structured as rounds rather than one long sit, with a cool-down between each; total heat exposure across the session is what the cardiovascular literature associates with outcomes, which is why the total is shown separately from the per-round figure.
Sauna session structure
Minutes per round = (20 - (temp - 80) x 0.6 - humidity x 0.15) x experience scale, bounded to 4-20; total session = rounds x (round + cool-down)
Guidance and estimates only, not medical advice. Sauna use causes substantial cardiovascular and thermal stress. Avoid alcohol before or during use, leave immediately if you feel faint or unwell, and seek clearance from a qualified health professional if you are pregnant or have a cardiovascular condition, low blood pressure or any condition affecting thermoregulation.
Two to four for most people, with cool-downs between. Beyond four the cumulative fluid loss becomes the limiting factor rather than heat tolerance, and the marginal benefit is small.
It does not need to be. A cool shower, outdoor air or simply sitting out works and is more accessible. Cold plunging between rounds intensifies the cardiovascular response, which is not appropriate for everyone.
Roughly half a litre per twenty-five minutes of sauna time, more in high humidity. Weighing yourself before and after is the accurate method — each kilogram lost is about a litre of fluid.