Working out on a heavy bag can burn between 354 and 558 calories per hour, depending on your weight and the intensity of the workout. However, you would already have to be in fairly good physical condition to punch a bag continuously for an hour, and depending on your schedule, you might not always have as much time as that. You can still burn a lot of calories even with a shorter workout.
The average man weighs around 168 pounds in his 20s, 179 in his 30s, and 182 in his 40s. The heavier you are, the more calories you burn in your workout -- about 2.72 calories per pound per hour when working out on the heavy bag. This means that a 15-minute heavy-bag workout should burn about 114 calories for a man weighing 168 pounds, nearly 122 calories for a man weighing 179 pounds and almost 124 calories for a man weighing 182 pounds.
Half an Hour
A workout of half an hour on the heavy bag should burn more than 228 calories for a man of average weight in his 20s, more than 243 calories in his 30s and more than 247 calories in his 40s. Of course, the longer the workout goes on, the more likelihood that you will lower the intensity whether consciously or not. These numbers only apply if you are able to maintain a consistent level of intensity in your workout.
If you weigh 168 pounds, 45 minutes on the punching bag should burn almost 343 calories. If you weigh 179 pounds, 45 minutes would burn about 365 calories. If you weigh 182 pounds, 45 minutes of punching should burn about 371 calories. These weights have been selected because they are the median weights for men in their 20s, 30s and 40s. To calculate how many calories you will burn in a heavy-bag workout, multiply your current weight by 2.72. The result will be the approximate number of calories you would burn in an hour on the heavy bag.
Other Boxing Workouts
Boxing involves a lot more than just hitting a heavy bag, so if you train at a full-service boxing gym you can expect to burn more calories. Besides the heavy-bag workout, you'll also be working on the speed bag, using a jump rope and sparring with other boxers. All of these activities combined could burn around 800 calories in an hour, which is much more than you could burn by working with a heavy bag alone. Also, a more varied workout reduces the chance of developing repetitive stress injuries from continuously repeating the same high-impact moves.