These numbers will convince you to swap your usual cardio workout for a swim.

By Ashley Mateo
July 11, 2019
Credit: PeopleImages/Getty Images

If you've ever jumped into a pool for a cardio workout, you know just how much harder swimming can feel compared to running and cycling. It may have seemed easy when you were a kid doing laps at camp; now, it's amazing how winded you can feel after just a few minutes.

The Benefits of Swimming

"Swimming is one of the best workouts out there," says Rochelle Baxter, an Aaptiv master trainer, AFAA certified personal trainer, and triathlete. "It helps burn fat, shed weight, build strength, and improve overall health." Not to mention, swimming is low impact, making it a great option for active recovery and injury prevention.

The reason swimming is so good for you is that every time you pull, kick, or perform a stroke, you're pulling against the resistance of the water, which is—duh—significantly more dense than air.

"This builds muscle and burns major calories," says Baxter. "While you're burning these calories, you're also building lean muscle, which means you will continue to burn calories throughout the day." (Here's more about the science of how building muscle helps you burn fat.)

How Many Calories Does Swimming Burn?

To figure out how many calories you burn while swimming, first you have to understand how scientists estimate the amount of energy your body uses during physical activity. The unit used is called a MET (or metabolic equivalent), and it measures how hard your body is working relative to rest. When you're lazing around on the couch (aka at rest), your body burns 1 MET, which is equivalent to 1 calorie per kilogram of bodyweight per hour.

If you know how many METs an activity "costs," and you know how much you weigh, you can calculate the number of calories you've burned doing that activity. Good news: There's no math required. You can use an online calculator, which takes into account your weight and the duration of the exercise, to easily determine your calorie burn.

While swimming, your body burns anywhere from 3.5 METs (223 calories per hour) treading water at a moderate effort; to 8.3 METs (528 calories per hour) for a medium-speed, vigorous effort crawl; and 13.8 METs (878 calories per hour) for butterfly stroke. (These estimates are for a 140-pound adult.)

For comparison's sake, jogging would compare at 7 METs (446 calories per hour) and bicycling at 7.5 METs (477 calories per hour), though the METs and calorie burn for these activities vary based on intensity, too. (FYI, other watersports like kayaking and stand-up paddleboarding burn calories too!)

What Factors Into Your Calories Burned While Swimming

But don't get caught up in those numbers. How many calories you burn swimming depends on many factors, says Bianca Beldini, D.P.T., a physical therapist, USA Triathlon-certified coach, and certified Schwinn Cycling instructor.

Your body: "Someone who weighs more will expend more calories than someone who weighs less because it takes more energy to move a larger body than a smaller one," she says. (Which, yes, is taken into account in the METs formula.) "But a larger body will also create more surface area in the water thus creating more drag resistance. More drag means it takes more energy to push through the resistance, therefore increasing the heart rate and resulting in higher caloric expenditure."

Your swim speed: How fast you can swim also affects your calorie burn. "The slower you swim, the less energy output there is, resulting in less calories burned," says Beldini. Hence, the faster you swim, the more energy you use. Using swim devices such as pull buoys, pull paddles, parachutes, and bands, to increase resistance or increase drag will also increase your energy output, upping your calorie burn, she adds.

Your swim stroke: And then, of course, there's the stroke itself. "Butterfly is probably the hardest and most technical stroke," says Baxter—that's why it burns the most calories. When you're doing the stroke, you're simultaneously performing a dolphin kick and your arms are coming fully overhead, which calls for serious, total-body muscle engagement (especially in your core and upper back), she says. A crawl is next in line for the number of calories burned swimming. "Every time you perform a stroke, you're also kicking!" says Baxter. "That's the perfect mixture for burning major calories." Breaststroke and backstroke are about equal in terms of caloric outcome. "These two are slower strokes, but you can still burn calories with proper technique," she says.

See below for some more specific estimates on the number of calories burned swimming each type of stroke. (Estimates are based on a 140-pound adult. Check out other swim stroke and speed MET estimates here and use this swimming calorie calculator to find your calorie burn.)

  • Treading water (moderate effort): 3.5 METs = 223 calories/hour
  • Backstroke: 4.8 METs = 305 calories/hour
  • Breaststroke: 5.3 METs = 337 calories/hour
  • Freestyle or crawl (light or moderate effort): 5.8 METs = 369 calories
  • Freestyle or crawl (medium to vigorous effort): 8.3 METs = 528 calories/hour
  • Freestyle or crawl (fast or vigorous effort): 9.8 METs =623 calories/hour
  • Butterfly: 13.8 METs = 878 calories/hour

How to Burn More Calories While Swimming

No matter your size, speed, or stroke, the best way to burn more calories while swimming is doing intervals of hard efforts interspersed with recovery time. (Related: How to Get More Out of Your Swimming Workouts)

"A sample interval set would look like this: A 50m freestyle sprint followed by a 10-second rest where your heart rate comes back down, repeated five times total," says Baxter. Those high-intensity efforts, with rest, tax your system way more than a steady state workout—and science shows that HIIT burns 25 to 30 percent more calories, plus taps into the afterburn effect, which burns calories even after your workout is over. (P.S. You can incorporate calorie-burning intervals into your running workouts too.)

Ready to give it a try? Next time you're looking to scorch calories without beating up your body, dive into these swimming workouts for every fitness level.