Does Sweating Burn Calories? What a Wet Shirt Tells You

The short answer to “does sweating burn calories” is no. Sweat is your skin getting rid of heat, and I found no measured calorie cost for making it. A wet shirt tells you how hot you got and how humid the room was. It says little about how much fuel you used. Hot rooms, saunas and sweat suits make you sweat harder, yet in the studies that measured breath, the extra energy was small or zero.

Does sweating burn calories, or does it just cool you down?

It cools you down. When sweat evaporates it takes heat along. The latent heat of vaporization of sweat is 580 kcal of heat per kilogram of sweat that evaporates, or 2,426 J per gram. A kilogram of sweat is about a liter.

That number is easy to misread. It is heat leaving your skin, not energy your body spent. The warmth came from your working muscles, or from the air and the sun when the day is hot. The same review notes that heat flows into the body from the air whenever the air is warmer than your skin.

I worked one sum to show why heat removed can’t be calories burned. Across 506 athletes, the average whole-body sweating rate was 1.21 L an hour, with a range of 0.26 to 5.73. If every drop evaporated, 1.21 L at 580 kcal per liter would carry away about 700 kcal of heat an hour.

Now take a 70 kg (154 lb) adult on a brisk walk. That walker burns 336 kcal an hour. I got it from 4.8 METs × 70 kg × 1 hour, since the Compendium counts 1 MET as 1 kcal per kg per hour. Put that walker in a hot park, sweating at the athletes’ average rate. The evaporating sweat would carry off about twice the walker’s fuel use. The rest of that heat would have to come from the hot air and the sun.

A wet shirt is also a poor gauge of cooling. When sweat is made faster than it evaporates, it pools and drips, and much of it falls away without taking heat with it. Humid air and thick fabric leave you wetter for the same effort.

Fitness changes the picture too, because the sweat gland review lists aerobic training among the things that raise whole-body sweating rate. A fit person can soak a shirt sooner than a beginner doing the same work. A drenched shirt can come from a muggy day as easily as from a hard workout, and a fit person gets there sooner.

What does it cost your body to make sweat?

Some, in principle. Secreting sweat and pulling sodium back out of it need ATP, and the glands run mainly on glucose burned with oxygen.

How much? I found no published measurement of the whole-body energy cost of producing sweat, so I won’t invent a figure. The closest evidence comes from studies that heat people up and measure all the energy they use. Four of them are in the table.

Study	Who and what	Energy found	How it was found
Faulkner et al., Temperature 2017	14 men, 60 minutes waist-deep in 40°C water or on a bike	Bath: +61.0 kcal an hour over rest. Bike: +556.3 kcal an hour	Gas exchange, measured
Matthews et al., J Strength Cond Res 2022	12 adults, the same interval session with and without a sauna suit	285 vs 271 kcal during, 123 vs 113 kcal in the next hour	Gas exchange, measured
Lambert et al., Int J Exerc Sci 2020	16 yoga practitioners, one hour of the same sequence at 105°F (40°C) and at 74°F (23.3°C)	No difference in oxygen use, heart rate or kcal	Gas exchange, measured
Podstawski et al., BioMed Res Int 2019	45 sedentary men, four 10-minute sauna rounds at 90–91°C	73 to 131 kcal per round	Heart-rate monitors, estimated

Start with the bath. Sitting in hot water raised energy use by about 79% over resting. That is a real effect. But the cycling session raised it by 556.3 kcal an hour, about nine times as much. The study measured the whole body, so it can’t say how much of the 61 kcal went to sweat glands. All 14 were men.

The sauna suit study comes closest to testing “sweat harder, burn more.” Twelve adults did ten 1-minute intervals at 85% of peak power. They did the session twice, once in a suit. The suit raised energy use by a statistically significant amount. The authors called it an increase of 23 kcal that may not benefit weight loss.

Core temperature was similar in both conditions. Fat oxidation rose for an hour afterward, but that is the fuel mix. The total moved by tens of calories at most.

How many calories does a sauna burn?

The only sauna calorie figures I found come from heart-rate monitors, and they look too high. The Podstawski study put 45 sedentary men, about 21 years old, through four 10-minute rounds at 90–91°C with 5-minute cool-down breaks. The monitors gave 73.04, 93.82, 114.91 and 131.40 kcal for the four rounds.

Added up, that is 413 kcal in 40 minutes of sauna, or about 620 kcal an hour. The same paper gives the men’s basal metabolic rate, read by a body-composition scale, as 1,815 kcal a day. That is about 76 kcal an hour. So the monitors credit men sitting still with eight times their resting rate. The bath study above measured breath and found an extra 61.0 kcal an hour. I doubt the sauna figure.

The authors name the Suunto Ambit3 Peak heart-rate monitors as a limitation and ask for work on how reliable such monitors are in extreme heat.

Heart rate is a weak stand-in for energy in the heat. A Colorado State exercise scientist said in a press release, not a paper, that hot rooms raise heart rate without necessarily raising metabolic rate. Heart-rate equations then overstate calories.

Heat also sends more blood to the skin. One review of sweat evaporation puts skin blood flow at about 0.25 L a minute at rest, and about 8 L under heat stress. Part of a sauna pulse is the heart moving that blood, not muscles burning more fuel. The hot yoga study below, which measured breath, found no jump in energy use.

What the sauna did measurably do was cost water. Across the 60-minute protocol, four rounds plus the breaks between them, the men lost 0.65 kg (1.4 lb) on average, which the authors call fluid.

Does hot yoga burn more calories than regular yoga?

Not in the best comparison I could find. Lambert’s team asked 16 experienced practitioners, 14 of them women, to do the same one-hour Bikram sequence on two days. One day was 105°F. The other was 74°F. A metabolic cart measured their breath. Mean and peak oxygen use, heart rate and kcal did not differ between conditions. The class cost about 156 kcal in the hot room and 151 in the cool one, for people averaging 60 kg (132 lb). The hot room did shift the fuel mix toward fat and gave a bigger hip stretch. The energy total stayed put.

Same result in a systematic review of 43 hot yoga studies, which covered 942 people. Acute hot yoga raised body temperature and heart rate, but not the energetic demand compared with unheated yoga. Only 3 of its 10 acute studies had an unheated comparison, though. It also put the sweat loss of a 90-minute Bikram class near 1.5 L. That is the wet mat. It isn’t a calorie count.

A 2014 Colorado State press release says some practitioners report burning as many as 1,000 calories in a class. Its own lab measured 19 experienced practitioners (11 women, 8 men) in a 90-minute Bikram class at 105°F and 40% humidity. They averaged about 330 kcal for the women and 460 kcal for the men, with a heart rate near 160 beats a minute. A yoga college and a yoga nonprofit funded the work. I found no peer-reviewed paper for it.

Hewett’s 2015 review of Bikram research lists unpublished conference data on 19 practitioners with 333 to 459 kcal per class. The sample size, the calorie range and a co-author named Fritz suggest the same data. But the review gives an average heart rate of 134, not 160. I can’t confirm they are one data set, so I treat 330 and 460 as preliminary.

The 2024 Compendium puts this in perspective. I multiplied each MET value by body weight to get kcal per hour, and these totals include the energy you use at rest anyway.

Activity (Compendium code)	METs	55 kg (121 lb)	70 kg (154 lb)	90 kg (198 lb)
Yoga, Hatha (02150)	2.3	127 kcal	161 kcal	207 kcal
Yoga, Hot (02155)	3.0	165 kcal	210 kcal	270 kcal
Walking, 3.5 to 3.9 mph, brisk (17200)	4.8	264 kcal	336 kcal	432 kcal

A chamber study of 24 adults, reported in that same review, put a whole Bikram class at 2.9 METs, close to the Compendium’s 3.0. Hot yoga sits between gentle yoga and a brisk walk. At 70 kg the gap over Hatha is about 49 kcal an hour.

The steps to calories calculator applies the same Compendium values to your weight and walking time. It separates the extra a walk adds from what you would burn anyway.

One limit on the table: Compendium values are group averages, and your own class could land above or below them. The Compendium marks estimated values in red, and the hot yoga code isn’t one of them. Still, the same people did the same poses at two temperatures. The energy did not differ. I wouldn’t log extra calories for heat. Pick a hot class if you like it. That is reason enough.

Is the weight you lose when you sweat fat?

No, it is water. The scale drop after a sauna or a hot class is fluid, and it comes back when you drink. The American College of Sports Medicine says the goal after exercise is to replace any fluid and electrolyte deficit. On how much, the sources differ. The Korey Stringer Institute at UConn says 150% of the body mass lost. Its own table on the same page lists 1 L for each 1 kg. The 2017 National Athletic Trainers’ Association statement says 100% to 150%, the top end when you have under 4 hours to recover. With more than 12 hours, it says normal food and drink is enough.

Body fat is a different store. Shifting it takes a run of deficit days, as how many calories a pound of body fat holds explains. Sweating a kilogram in one session moves the number on the scale and nothing else.

The same ACSM position stand aims to keep water loss under 2% of body weight during exercise, to avoid compromised performance. It also says you can estimate your own sweat rate by weighing before and after. At 70 kg (154 lb), 2% is 1.4 kg (3.1 lb). Here is the sum for one 60-minute class, using invented but plausible numbers.

• Before: 70.0 kg. After: 69.2 kg, so 0.8 kg (1.8 lb) lost.
• You drank 0.5 L during the class. Sweat is 0.8 + 0.5 = 1.3 L, a rate of 1.3 L an hour.
• You lost 0.8 ÷ 70 = about 1.1% of your weight, under the 2% mark.
• To replace it: 0.8 L at 100%, or 0.8 × 1.5 = 1.2 L at 150%. The higher figure fits a second session within 4 hours.

Trust the next morning’s reading over the one right after class, when you are still short of water. If you track your weight, a week of mornings shows the trend, and one sweaty day washes out of the average.

What should you do after a sweaty workout?

Weigh yourself before and after one workout this week, using the same scale and little clothing, and note any water you drank. Divide the total by the hours to get your own sweat rate. The replacement range is 100% to 150% of the weight you lost, the top end if you train again within 4 hours.

Log the workout by what you did and for how long, not by how wet you got. Cost follows the work. A lifting session can leave you dry and still use real energy, as how many calories weight lifting burns shows. For walking, calories burned walking gives the per-mile numbers.

Be wary of the calorie figure on your wrist in the heat. Watches estimate burn from heart rate and motion, and Apple Watch calorie accuracy shows how loose those estimates are even in a cool room. A hot studio adds the heart-rate problem described above. Whatever the watch says, the figure sits inside your daily total, which how many calories you burn a day lays out. To see which workouts do burn the most, what exercise burns the most calories ranks ten of them by the hour.

Heat is also a safety matter. Dizziness, nausea, a headache or confusion in a hot room mean stop and cool down. The NHS lists heatstroke as a medical emergency, and the hot yoga review notes that cases of ill health and heat illness have been reported. With a heart or blood pressure condition, ask your doctor before using a sauna or a heated studio.

Next time you leave a class dripping, step on the scale and write down the minutes. Those two numbers are worth keeping. The shirt is not.