Sauna Water Loss Calculator: How Much to Drink After

A single sauna session can quietly cost you a litre of fluid, mostly as sweat, and the tiredness or headache people blame on the heat is often just mild dehydration. Enter your weight, how long you sit and how hot the cabin runs, and this tool estimates the fluid you lose and how much to drink to replace it.

The estimate uses your total time in the heat, a sweat rate that rises with cabin temperature, and a small adjustment for body size (a heavier body sweats more to shed the same heat). Sweat loss varies a lot between people, so treat the figure as a guide, not a medical reading.

How to rehydrate well: sip steadily over the hour or two after your session rather than downing it all at once, which just passes straight through. If you have lost more than a litre, or you sauna often, add a pinch of salt to a drink or use an electrolyte sachet, because plain water alone does not replace the sodium you sweat out. If you feel dizzy, get a headache or stop sweating during a session, leave the heat and cool down.