Since one pound has the calorie equivalent of 3,500 calories, you would have to walk at 5 mph for five hours and 40 minutes to burn the caloric equivalent of one pound. Even that isn't a reliable marker because the more you weigh, the more calories you burn.
A 120-pound person would burn less calories in the same amount of time, walking at the same speed, as a 200-pound person. Use the American Council on Exercise's physical activity calorie calculator for your exact weight.
125-Pound Person
A 125-pound person burns 85 calories walking 2 mph for 45 minutes and 140 calories walking 3 mph. A faster pace of 4 mph burns 212 calories.
150-Pound Person
A 150-pound person burns 102 calories walking 2 mph for 45 minutes and 168 calories walking 3 mph. A faster pace of 4 mph burns 255 calories.
175-Pound Person
A 175-pound person burns 119 calories walking 2 mph for 45 minutes and 196 calories walking 3 mph. A faster pace of 4 mph burns 298 calories.
200-Pound Person
A 200-pound person burns 136 calories walking 2 mph for 45 minutes and 224 calories walking 3 mph. A faster pace of 4 mph burns 340 calories.
Customize Your Caloric Burn
If you're curious exactly how many calories you're actually burning, use a calorie tracking app like LIVESTRONG's MyPlate, which can also connect to your fitness tracker.