According to WebMD, someone who weighs 150 pounds will burn 273 calories by riding a bike at a leisurely pace for an hour. The exact amount of calories burned by cycling depends on the intensity of the ride, how long the ride lasts and how much the cyclist weighs.
The faster a cyclist rides a bike, the more calories he will burn according to WebMD. For example, an hour of cycling for a 150 pound person burns 409 calories when riding at a speed between 10 and 11.9 miles per hour. An hour of cycling by the same person at a speed between 14 and 15.9 miles per hour burns 682 calories in an hour.
A longer bike ride burns more calories than a shorter bike ride because the activity lasts longer. The amount of calories burned increases as the weight of the cyclist increases. An hour of cycling at a speed between 14 and 15.9 miles per hour for a person that weighs 300 pounds burns 1,364 calories.