How much weight do you lose in a sauna?

Podstawski and colleagues, ScientificWorldJournal, 2014 weighed 674 students aged 19 and 20 before and after two 10-minute rounds in a dry sauna at 90°C (194°F) with a 5-minute break. Heavier people lost more, in kilograms and as a share of their weight:

Group	Average loss	Share of body weight
Women, underweight	0.25 kg (0.6 lb)	0.5%
Women, normal weight	0.34 kg (0.7 lb)	0.6%
Women, overweight or obese	0.7 kg (1.5 lb)	0.9%
Men, underweight	0.32 kg (0.7 lb)	0.5%
Men, normal weight	0.42 kg (0.9 lb)	0.6%
Men, overweight or obese	0.82 kg (1.8 lb)	0.9%

A longer visit takes more. In a second study, 45 young overweight, inactive men did four 10-minute rounds at 90 to 91°C (194 to 196°F) with 5-minute breaks, and lost 0.65 kg (1.4 lb) over the hour.

Both studies used a dry Finnish-style sauna at about 194°F. Infrared cabins commonly run at 110 to 140°F, as our infrared vs traditional guide explains, so the same minutes can mean a different loss. That is why your own before and after weights beat any average.

The American College of Sports Medicine position stand on exercise and fluid replacement, 2007 says sweat losses can be estimated by weighing before and after, and that the goal afterwards is to replace the fluid and electrolytes you lost. It also notes that sweat rates vary a lot between people, which is the case for measuring your own.

Drinking exactly what you lost is not enough. In a study by Shirreffs and colleagues, people had to drink more than they had sweated to restore their fluid balance, and unless the drink carried enough sodium the extra mostly left as urine. Rehydration studies since have given people 1.5 times their loss: with a meal, plain water worked, and milk was retained better than water or a sports drink. The calculator shows that 1.5 times figure as the volume those studies used. Spread it over the next few hours rather than all at once.

Our guide to whether you need electrolytes after a sauna covers what sweat takes out besides water.

If you have been told to limit fluids, for heart failure for example, MedlinePlus notes that limiting how much you drink can be part of your care. Follow your doctor's limit rather than this page's number, and ask before using a sauna at all.

How much weight do you lose in a sauna in 20 minutes?

In the largest study we found, 674 young adults spent 20 minutes in a sauna as two 10-minute rounds in a dry sauna at 90°C (194°F) with a 5-minute break. Women lost an average of 0.37 kg (0.8 lb) and men 0.5 kg (1.1 lb), and the most anyone lost was 1.3 kg (2.9 lb). Heavier people lost more.

How much weight do you lose in a sauna in 30 minutes or an hour?

We found no large study that timed one continuous 30- or 60-minute stay. In a 2019 study, 45 young overweight men did four 10-minute rounds at 90 to 91°C (194 to 196°F) with 5-minute breaks and lost 0.65 kg (1.4 lb) over the hour. Longer and hotter sessions take more, so your own scale is the better guide: weigh yourself before and after and use the calculator on this page.

Is the weight you lose in a sauna fat?

No. It is sweat, which is water, and the studies measure it as fluid to be replaced. It comes back when you drink. A sauna burns few calories, which our guide to whether an infrared sauna burns calories explains.

How much water should I drink after a sauna?

Weigh yourself before and after, without clothes or with the same dry clothes. Each kilogram lost is about a liter of sweat, and each pound about 15 fluid ounces. Rehydration studies give people 1.5 times what they lost, because part of what you drink leaves as urine, and a meal or a drink with some sodium helps you keep it. If you have been told to limit fluids, for heart failure for example, follow that limit instead.

How much sweat loss is too much?

The American College of Sports Medicine's fluid guidance treats a loss of more than 2% of body weight as excessive dehydration to prevent during exercise. In the 674-person sauna study, the group averages ranged from about 0.5% to 0.9% of body weight. If you lose more than 2% in a session, make the next one shorter or cooler.