An individual who weighs 155 pounds burns 493 calories per hour while swimming at a slow pace. That same individual swimming at fast pace burns 704 calories per hour.
Calories burned swimming laps varies greatly depending on the weight of the individual and the speed at which they are swimming. The swim stroke also plays a role in calories burned, but the swimmer's weight is highly important, as well.
The butterfly stroke burns the most calories, followed by the fast freestyle and breast strokes, which burn the same number of calories per hour. The backstroke and slow freestyle stroke burn the fewest calories.