According to the Swimming Calculator by Endless Pools, if you swim at a 1:30 pace per 100 yards, you will burn these approximate amount of calories: Butterfly - 302 calories per 1000 yards Backstroke - 270 calories per 1000 yards Breaststroke - 260 calories per 1000 yards Freestyle - 250 calories per 1000 yards Click the Swimming Calculator here for more