The number of calories you'll burn speed walking depends on your current body weight and your speed. If you speed walk for two hours, however, you'll likely expend a significant number of calories, and if you do so on a regular basis you may start to lose weight. A 2009 review in "The Ochsner Journal" reported the recommendation for 250 to 300 minutes of aerobic exercise -- such as walking -- weekly to enhance weight loss and prevent weight regain.
The more you weigh, the more calories you'll burn speed walking for two hours at the same pace as a smaller person. Harvard Health Publications reports that 185-pound individuals expend 712 calories walking for two hours at a pace of 3.5 mph, 800 calories walking at a pace of 4 mph and 888 calories at a pace of 4.5 mph.
Adults who weigh 155 pounds expend fewer calories speed walking than a 185-pound person. A 155-pound adult burns 596 calories walking at a pace of 3.5 mph for two hours, 668 calories walking 4 mph and 744 calories walking 4.5 mph.
Although 125-pound adults expend fewer calories than those of heavier weights, they still burn a significant number of calories speed walking for a two-hour time period. If you weigh 125 pounds, you'll burn 480 calories walking at a pace of 3.5 mph, 540 calories walking 4.0 mph and 600 calories walking 4.5 mph.
Burning 500 to1,000 more calories than you consume daily will help you drop about 1 to 2 pounds per week -- which is a safe rate of weight loss, according to the Centers for Disease Control and Prevention. If you don't have two hours each day to devote to speed walking, try participating in 45 to 60 minutes of aerobic exercise daily and consuming 500 fewer calories a day.