Quick answer: 30 minutes of medium-speed front crawl (about 50 yards a minute, 8.0 METs) burns about 299 kcal for a 160 lb (72.6 kg) swimmer. Slow, easy freestyle laps (5.8 METs) come to about 217 kcal in the same half hour, and butterfly (13.8 METs) about 515 kcal.
Choosing the right line
Swimming has no simple speed equation like walking or running, because drag, technique and body position vary so much between swimmers. Instead, this calculator uses the 2024 Adult Compendium of Physical Activities, the standard reference list that gives each activity a MET value. The list includes freestyle at several speeds (with yards per minute for the crawl entries, which helps if you time your laps), breaststroke and backstroke at a recreational and a training level, butterfly, treading water and a 5k open water swim. Pick the one closest to what you did; if you mixed strokes, run the calculator once per part and add them.
To find your crawl speed in yards per minute, divide the yards you swam by the minutes it took: 1,500 yards in 30 minutes is 50 yards a minute, which matches the medium-speed entry.
The arithmetic
One MET equals 3.5 ml of oxygen per kg of body weight per minute. For 8.0 METs and 72.6 kg: 8.0 x 3.5 x 72.6 / 1,000 = 2.03 litres of oxygen a minute. At 4.9 kcal per litre (the ACSM conversion), that is 10.0 kcal a minute, so about 299 kcal in 30 minutes. A handy shortcut for the same swimmer: every MET is worth about 37 kcal per half hour. The net figure removes one MET, the energy you would use at rest anyway.
Half an hour at each level (160 lb swimmer)
Recreational backstroke: about 179 kcal. Recreational breaststroke: 198. Fast freestyle laps: 366. Fast crawl at about 75 yards a minute: 392. Training breaststroke: 385. Training backstroke: 355. Elite competition crawl: 541. Moderate treading water: 131.
Keep in mind
- MET values are averages for adults. Technique varies between swimmers, so the same time at the same speed can cost two people different amounts.
- Rest at the wall counts in the time you enter unless you subtract it.
- Waterproof watches estimate swimming calories with their own models and may read differently.
- These are energy estimates only and are no promise of weight loss.
Working out your speed in the pool? Use the swim pace calculator. For a full race, see the triathlon calculator, or compare with the rowing calorie calculator.
Sources: Herrmann et al. (2024), 2024 Adult Compendium of Physical Activities, J Sport Health Sci; 2024 Adult Compendium: water activities; ACSM's Guidelines for Exercise Testing and Prescription, Table 7.3 metabolic calculations (as reproduced by Texas Tech University). Rules checked . Found a problem? Tell us.
Questions
How many calories does swimming burn in 30 minutes or an hour?
For a 160 lb swimmer: about 217 kcal in 30 minutes of slow freestyle laps (433 in an hour), 299 kcal for medium-speed crawl at about 50 yards a minute (597 in an hour), and 392 kcal for fast crawl at about 75 yards a minute (784 in an hour).
Which swimming stroke burns the most calories?
In the 2024 Compendium, butterfly is 13.8 METs, the highest stroke entry apart from elite competition crawl (14.5 METs). Recreational backstroke is the lowest at 4.8 METs.
Does treading water burn calories?
Yes. The Compendium lists moderate treading water at 3.5 METs (about 131 kcal in 30 minutes for a 160 lb person) and fast, vigorous treading at 9.8 METs.
Is swimming better than running for calories?
Per hour it depends on effort. Medium crawl at 8.0 METs is close to the Compendium's 8.5 METs for running at 5.0 to 5.2 mph. The calories follow the intensity, not the sport.