Many people use the treadmill for a low-impact walking workout, or as a warm up for other activities. Moderate use of the treadmill does burn calories, though not as many as running. According to caloriesperhour.com, a website that lists calorie-burning figures for thousands of activities, a 150-pound person who walks for one hour at 4 mph will burn 272 calories.
The faster you walk or run, the more calories you burn. According to caloriesperhour.com, a 150-pound person will burn nearly 800 calories by running 7 mph for an hour--a brisk jogging pace.
Many treadmills have adjustable settings that make you run or walk on an incline. Because this requires more energy, it burns more calories. According to caloriesperhour.com, a 150-pound person who walks at 4 mph on a 5 percent incline will burn 456 calories an hour. The same person will burn 646 calories an hour by walking at the same speed on a 10 percent incline.
One major factor that affects calorie burning is your size. The bigger you are, the more energy it takes to move your body. So while a 150-pound person will burn 272 calories an hour by walking on a treadmill at 4 mph, a 250-pound person will burn 454 calories an hour.
Many treadmills have on-board calorie counters to tell you how many you've burned during your workout. These are not completely accurate, but newer treadmills will give more accurate read outs than older ones. Calorie counters are most accurate when you enter information about yourself--namely your gender, age and weight.