When I did a google search on how to calculate how many calories you burn during your workout, eHow.com offers the following tips, click on the link below:
How to Calculate How Many Calories You Burn eHow.com
Below is a link to the Health Status Calculator mentioned in the article.
Here are my results for 60 minutes of boxing on a bag:
According to the information you provided, below is an estimate of the calories you burn. Generally, to maintain your weight, the amount of calories you take in should equal the amount you burn. The Daily Energy Expenditure calculator will help you figure out the minimum number of calories your body needs each day to work properly. To lose one U.S. pound (.454 kg), you must burn 3,500 more calories than you take in as food.
Activity Calories burned
Boxing – punching bag 440
Total Calories Burned 440