How Much Weight Can I Lose if I Swim 3 Hours a Week?

Exercise is one of the two traditional methods for losing weight. As a cardiovascular exercise, swimming works as well as many other options for weight loss. Exactly how much weight somebody can lose with a program of regular swimming varies according to an array of factors. However, some baseline assumptions can give you a general idea.

How Exercise Causes Weight Loss

The simple act of living burns calories. You burn calories as you breathe, sit up, type on your computer, drive your car and go about your daily life. When you exercise, you burn additional calories during your workout session. This immediately increases the number of calories you burn during that day. Further, exercise increases your general metabolic rate for hours -- or even days -- after you finish your workout. This is because your body works harder to refresh supplies of hormones and other chemicals you burn during exercise. When you burn more calories than you take in through eating and drinking, your body burns fat as a fuel. As that fat burns, you lose weight. To lose 1 pound, you need to burn 3500 more calories than you ingest.

Calorie Burn

Health resource website provides calorie information for many common exercises. Its calculator estimates a 160-lb. person will burn approximately 1,300 calories in three hours of moderate swimming and about 2,100 calories in three hours of vigorous swimming. At 3,500 calories per pound of fat, the workouts themselves would mean losing 1/3 to 2/3 of a pound per week just from the direct exercise. Heavier people will burn more calories in the same workout, while lighter people will burn less.

Metabolic Burn

There are no easy ways to calculate how many extra calories your body burns during the post-workout bump in metabolism. Oregon-based fitness coach Ben Cohn advises that, as a rule of thumb, you can safely add 50 percent to whatever your workout burned to get a general idea. However, Cohn warns that this is a gross overgeneralization and should be used only as an approximate guide. By that metric, a 160-lb. person could expect to lose up to 1 lb. per week with three hours of vigorous swimming.

Other Factors

Calorie counting is an inexact practice, as much an art as it is a science. This is because of the wide array of factors that will affect how many calories you burn in a workout session. Some other common contributors include the temperature of the air and water, what swimwear you have on, your swimming technique and even your mood while swimming. Your diet and lifestyle while you're swimming regularly will also have a strong effect on your ultimate weight-loss results.