Estimating percentage of body fat

The percent of your weight that is fat can be estimated by using the following methods. All of these methods have advantages and disadvantages and have margins of error.

• Underwater weighing. This is also called hydrodensitometry and is based on the principle that fat tissue is less dense than muscle and bone. Although it is the best method for measuring body composition, it is usually only done at universities and research facilities.
• Skinfold thickness. An instrument called a caliper is used to measure the thickness of fat at one or more sites on the body. Measuring skin-fold thickness gives a reasonable estimate of body fat composition, especially if taken from several sites. However, the results can vary when different people take the measurements or if the person taking the measurements is not well-trained.
• Bioelectrical impedance. A small electrical current is passed through your body, allowing the electrical resistance of your body to be measured. Bioelectrical impedance measurement of body fat is based on the principle that lean body mass conducts electricity better than fat body mass. Along with the electrical resistance, your height and weight are used to calculate your percent of body fat. There are some devices, including body fat scales, that you can buy to calculate your percent body fat using this method. Results can vary based on how much water is in your body and where the electrodes are placed.

Experts differ in their opinions about what is a healthy percentage of body fat. In general, 10% to 25% body fat is considered healthy in an adult man, and 18% to 32% body fat is considered healthy in an adult woman. Above this level is considered unhealthy.

Percentage of body fat will vary between different population groups. Your age, sex, and activity level will also affect your percentage of body fat. For example, endurance runners have less body fat than swimmers. People living near the North or South Pole generally have more body fat than people living in more moderate temperature zones.