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How to Measure Body Fat

By Kim Nunley

Knowing your body fat percentage can help you adjust your workout regimen and tailor your fitness goals. Many athletes also monitor body fat to help them know how to keep their bodies at an optimum performance level. Healthy body fat percentages vary between men and women, as women need more essential fat to keep their bodies functioning at a normal physiological level. There are a number of ways to measure your body fat, including the body mass index equation, waist circumference measurement, the skinfold test, bioelectric impedance, dual energy x-ray absorptiometry and hydrostatic weighing. These vary in ease and accuracy, so it's best to pick the one that fits your fitness, athletic and physiological needs.

Body Mass Index

Finding your body mass index, or BMI, is the quickest and easiest way to get a rough estimate of your body fat percentage. After using a scale to find your body weight in pounds and a measuring tape to acquire your height in inches, divide your weight in pounds by your height in inches squared and then multiply that value by 703. A score of 18.5 or lower is considered underweight, while a score of 18.5 to 24.9 falls into the normal category. A score of 25 to 29.9 is considered overweight, while anything 30 or over falls into the obese category. These scoring categories apply to both men and women. The Centers for Disease Control and Prevention explains that the formula doesn't directly measure body fat, but that BMI measurements do correlate to more precise measures of body fat, such as hydrostatic weighing. While quick and easy, the body mass index doesn’t take into account the percentage of types of tissues that make up your body weight. A person with low body fat but large amounts of muscle can weigh the same as someone with high body fat and low amounts of muscle, thus causing them to receive the same BMI score.

Skinfold Test

The skinfold body-fat test involves the use of a skin caliper that pinches the thickness of extra fat at specific areas of the body. Areas that are measured include the thighs, back of the upper arms, chest, stomach and the area above the pelvis, at the side of the ribs and under the shoulder blades. The readings from each of the seven sites are then used in a mathematical equation -- which is different for men and women -- to determine body fat percentage. Using the skin caliper correctly requires a trained test administrator. While the skinfold test is relatively easy and quick, it is highly susceptible to test administrator error. Find a quality test administrator at a fitness center or gym.

Bioelectric Impedance

Testing your body fat percentage with bioelectric impedance involves placing small electrodes at particular areas of your body. Small, unnoticeable electric currents are then sent through your body to measure how much resistance the electrodes experience. The more fat you have, the more resistance the electrical currents face. Many fitness centers and health clinics offer bioelectric impedance testing. The process is non-invasive, painless and takes just a few minutes to complete, but the accuracy of the results can be affected by dehydration. Be sure to drink eight 8-ounce glasses of water in the three days leading up to your test to make sure your results aren't affected.

Dual Energy X-ray Absorptiometry

Dual energy x-ray absorptiometry, or DEXA, measures the rate at which x-ray beams pass through your body. How quickly the beams pass through changes depending on whether they’re traveling through lean tissue, like muscle and bone, or fat. The test is highly accurate, but because of its high cost and the special equipment needed, it’s a procedure typically only used for research purposes or by professional athletes. You'll find DEXA machines at medical research centers and universities.

Hydrostatic Weighing

For a highly-accurate body fat measurement, visit a college university fitness department or a high-end fitness center for a hydrostatic weighing test. Hydrostatic, or underwater, weighing is the most accurate of the body fat tests, but it’s also the most involved and most expensive. After you submerge yourself underwater and expel all the air from your lungs, the amount of water that your body displaces is measured. That measurement can then be used to calculate body volume, body density and body fat percentage.

Waist Circumference

If you're interested in learning your body fat percentage because you're worried about being overweight and the associated health risks, you can simply measure your waist circumference. While measuring your waist circumference won’t tell you your exact body fat percentage, it will let you know if you’re at a higher risk of obese-related diseases. Excess fat centered around the waist is a sign that you could be at a greater risk of heart disease and type 2 diabetes. Men whose waists have a circumference of 40 inches or more are at a greater risk. For women, the risk is higher when their waist circumference is 35 inches or more. If your waist circumference is too high, use the other body fat tests to get a more accurate body fat measurement and visit your medical professional to determine if you really are at greater risk.

Body Fat Percentage Ratings

Except for BMI calculation and waist circumference measurement, each of the body fat tests will give you your actual percentage of body fat. You can use these values to determine where your body fat rates in terms of rating classification. For women, a body fat percentage of 8 to 15 is considered athletic, while 16 to 23 falls under good, 24 to 30 is rated acceptable, 31 to 36 is considered overweight and 37 receives a rating of obese. For men, a body fat percentage of 5 to 10 is considered athletic, while 11 to 14 is considered good, 15 to 20 is acceptable, 21 to 24 falls under overweight and 24 and above is considered obese.

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