Based on a 150-pound person, 30 minutes of moderate-speed walking burns about 160 calories. This figure varies depending on the person's weight and his total speed; a 125-pound person burns about 135 calories in 30 minutes walking 4 mph, whereas a 185-pound person burns about 200 calories.
A slower walk, about 3.5 mph, burns about 120 calories in 30 minutes in a 125-pound person, 150 calories in a 150-pound person and 180 calories in a 185-pound person. Walking more quickly, about 4.5 mph, burns about 150 calories in a 125-pound person, 185 calories in a 150-pound person and 225 calories in a 185-pound person. Caloric output can be increased by walking faster or by adding weight with dumbbells, a weighted belt or a loaded backpack.