The average person burns 430-575 calories per hour swimming leisurely. The number of calories you burn swimming will depend on your weight and the distance and speed you swim. A 150-pound (68kg) person swimming recreational backstroke will burn 344 calories per hour.

On average, swimming for 30 minutes can burn approximately 200-350 calories, depending on factors such as intensity, stroke used, and individual body weight.

Harvard Health estimates the calories burned by a 155-pound person engaging in moderate swimming activities to be roughly 223 calories per 30 minutes. Calorie expenditure can jump to 372 calories in the same timeframe for vigorous swimming.

While swimming, your body burns roughly 3.5 MET (about 223 calories per hour) with less intensity. About 8.3 MET (528 calories per hour) can be lost at moderate intensity. The body can burn 13.8 MET (878 calories per hour) under vigorous swimming.