A 70 kg swimmer burns about 420 kcal in 45 minutes of moderate freestyle
Calories burned while swimming are estimated as intensity (MET) × body weight (kg) × time (h). A MET compares an activity with sitting at rest, which counts as 1. The 2024 Adult Compendium of Physical Activities defines 1 MET as 1 kcal per kilogram of body weight per hour.
The calculator above uses the Compendium's 13 swimming and water-exercise values with their codes, unchanged. Even within freestyle the value moves from MET 5.8 at an easy pace to 8.0 at about 50 yards/min (≈46 m) and 10.5 at about 75 yards/min (≈69 m), so how hard you swim matters more than which stroke you pick.
How to use the calculator
- Enter weight and time: type your weight in kilograms and the minutes you actually spent swimming. The 30, 45, 60 and 90 minute buttons are shortcuts. If you rested for a long stretch, leave that time out.
- Pick the activity and intensity: freestyle, backstroke and breaststroke are split into easy and training effort. If you are too out of breath to talk, you are closer to training effort.
- Read the result: the large number is total calories burned. Below it you get the net calories from exercise, the amount per 10 minutes and per hour, and, if you enter a target, how long it takes to burn it.
- Compare activities: the bars below compare all 13 activities at the same weight and time. Tap a bar to calculate for that activity.
Formulas
| Value | Formula | 70 kg · moderate freestyle · 45 min |
|---|---|---|
| Calories burned | MET × weight × hours | 8.0 × 70 × 0.75 = 420 kcal |
| Net calories | (MET − 1) × weight × hours | 7.0 × 70 × 0.75 = 368 kcal |
| Time to reach a target | target kcal ÷ ((MET − 1) × weight) × 60 (net) | 300 kcal → about 37 min |
| Distance (freestyle only) | meters per minute × minutes | 45.72 m × 45 = about 2,060 m |
Many other calculators convert 1 MET as 3.5 mL of oxygen per kg per minute (MET × 3.5 × weight ÷ 200, per minute). That works out to 1.05 kcal/kg per hour and gives results about 5% higher (441 kcal in the example above). This calculator follows the Compendium definition as written.
MET and calories by activity
Values from the 2024 Compendium table of water activities. Calories are for a 70 kg person swimming 45 minutes.
| Activity (code) | MET | Calories | Net |
|---|---|---|---|
| Butterfly (18270) | 13.8 | 725 kcal | 672 kcal |
| Freestyle, fast, ~75 yards/min (18280) | 10.5 | 551 kcal | 499 kcal |
| Breaststroke, training or competition (18260) | 10.3 | 541 kcal | 488 kcal |
| Backstroke, training or competition (18250) | 9.5 | 499 kcal | 446 kcal |
| Freestyle, moderate, ~50 yards/min (18290) | 8.0 | 420 kcal | 368 kcal |
| Sidestroke (18320) | 7.0 | 368 kcal | 315 kcal |
| Leisurely swimming, not lap swimming (18310) | 6.0 | 315 kcal | 263 kcal |
| Freestyle, light effort (18240) | 5.8 | 305 kcal | 252 kcal |
| Water aerobics (18355) | 5.5 | 289 kcal | 236 kcal |
| Breaststroke, recreational (18265) | 5.3 | 278 kcal | 226 kcal |
| Backstroke, recreational (18255) | 4.8 | 252 kcal | 200 kcal |
| Water walking, moderate pace (18368) | 4.8 | 252 kcal | 200 kcal |
| Treading water, moderate effort (18350) | 3.5 | 184 kcal | 131 kcal |
By body weight
Calories scale with body weight. These values are for 30 minutes.
| 30 min | 50 kg | 60 kg | 70 kg | 80 kg | 90 kg |
|---|---|---|---|---|---|
| Freestyle, moderate (MET 8.0) | 200 | 240 | 280 | 320 | 360 |
| Breaststroke, recreational (MET 5.3) | 133 | 159 | 186 | 212 | 239 |
| Butterfly (MET 13.8) | 345 | 414 | 483 | 552 | 621 |
Distance and round trips
Only two Compendium rows state a speed: moderate freestyle (about 50 yards/min, roughly 45.7 m) and fast freestyle (about 75 yards/min, roughly 68.6 m). The calculator estimates distance for those two and converts it to round trips (there and back) in a 25 m and a 50 m pool. Moderate freestyle for 45 minutes comes to about 2,060 m, which is 41 round trips in a 25 m pool or 20 round trips in a 50 m pool. In practice, push-offs from the wall and rests make the real figure differ.
Getting a more accurate number
- Leave out rest time: enter the time you actually swam, not the time you were at the pool. In a one-hour lesson the swimming time is often shorter.
- Judge intensity by breathing: if you cannot keep a conversation going, choose training effort. If you can talk, choose an easy effort.
- Set goals with net calories: when comparing with a weight goal, net calories, which exclude what you burn at rest anyway, are a better match.
- Compare with a sports watch: if you have a heart-rate device, reading it alongside this estimate helps you choose an intensity that fits you.
Common mistakes
- Entering the whole lesson: counting instructions and waiting time inflates the calories considerably.
- Choosing intensity by stroke alone: breaststroke is MET 10.3 at training effort and 5.3 when recreational, nearly double for the same stroke.
- Treating total calories as calories lost: the total includes what you burn at rest. The extra calories from exercise are the net figure.
Limits and cautions
- MET values are averages for adults aged 19 to 59. Actual use varies with stroke technique, body composition, water temperature and age.
- You can enter a weight from 20 to 300 kg and a time from 1 to 600 minutes. The result is an estimate for swimming at the same intensity without stopping.
- If you have a heart or lung condition, or are starting exercise for the first time, talk to a professional before choosing an intensity. This calculator is not medical advice.
Reference date The MET values and the definition of 1 MET were checked on the 2024 Adult Compendium website on 2026-10-09.
Sources
- 012024 Adult Compendium of Physical Activities: Water ActivitiesMET values and codes for swimming and water exercise (18230 to 18377)
- 02Herrmann SD, et al. 2024 Adult Compendium of Physical Activities. J Sport Health Sci. 2024;13(1):6-121 MET = 1 kcal/kg/h (≈ 3.5 mL O2/kg/min), adults aged 19 to 59
Frequently asked questions
How are swimming calories calculated?
Calories burned (kcal) = MET × body weight (kg) × time (h). The 2024 Compendium defines 1 MET as 1 kcal per kilogram of body weight per hour. A 70 kg person swimming moderate freestyle (MET 8.0) for 45 minutes burns 8.0 × 70 × 0.75 = 420 kcal.
Which stroke burns the most calories?
By 2024 Compendium values, butterfly is highest at MET 13.8, followed by fast freestyle at 10.5, training breaststroke at 10.3 and training backstroke at 9.5. The same stroke done recreationally drops by almost half, to 4.8 for backstroke and 5.3 for breaststroke, so intensity matters more than the stroke itself.
What are net calories?
Net calories are the extra calories you burn because of exercise, after subtracting what you would burn at rest (1 MET). The formula is (MET − 1) × weight × time. For 70 kg swimming moderate freestyle for 45 minutes, the total is 420 kcal and the net is 368 kcal. Net calories are the better match when you compare with a weight goal.
Why does my result differ by about 5% from other calculators?
A formula that converts 1 MET as 3.5 mL of oxygen per kg per minute (MET × 3.5 × weight ÷ 200) gives 1.05 kcal per kg per hour, which is about 5% higher. This calculator uses the Compendium definition as written (1 MET = 1 kcal/kg/h). For 70 kg, moderate freestyle and 45 minutes that is 420 kcal versus 441 kcal.
How many calories does 30 minutes of swimming burn?
It depends on weight and intensity. At moderate freestyle (MET 8.0), 30 minutes burns 200 kcal at 50 kg, 240 kcal at 60 kg, 280 kcal at 70 kg and 320 kcal at 80 kg. Recreational breaststroke (MET 5.3) drops to 186 kcal at 70 kg.
Can it also tell me how far I swam?
Only for moderate freestyle (about 50 yards/min, roughly 46 m) and fast freestyle (about 75 yards/min, roughly 69 m), the two rows where the Compendium gives a speed. Moderate freestyle for 45 minutes comes to about 2,060 m, or 41 round trips (there and back) in a 25 m pool. Other strokes have no speed reference, so no distance is shown.
Can I trust the swimming calorie result?
Treat it as an average estimate. MET values are averages for adults aged 19 to 59, and actual use varies with stroke technique, rest time, water temperature and body composition. The result assumes you swam at the same intensity without stopping, so leave out rest time to stay close to reality.
Is my weight stored?
No. The calculation runs only in this browser, and your weight is not kept in the address, browser storage or on any server.