Of everything that makes up your body weight, your percentage of body fat is one of the most important to know from a health standpoint.

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How much you weigh isn’t nearly as important for your health and well-being as your body composition. The number on the scale reflects the combined weight of all your body’s tissues—water, fat, and lean tissues (muscle, bone, internal organs, and connective tissue). Of everything that makes up your body weight, your percentage of body fat is one of the most important to know from a health standpoint.

Knowing how to calculate body fat and use a body fat percentage chart can help you stay focused on your diet and exercise and motivated to stay healthy. Plus, it can help uncover whether hidden fat is damaging your health—despite your normal body weight.

While it is essential to maintain some body fat for insulation and heat conservation, as metabolic fuel for the production of energy, and as a cushion for your internal organs, excess fat indicates increased risks for cardiovascular disease, metabolic syndrome, diabetes, cancer, and many other disorders. Furthermore, if you are in the process of losing weight, it is common to lose too much muscle and not enough fat, leaving you thinner but not any healthier, and more prone to quickly regaining the fat lost, and then some. We discuss this more below. But first, let’s review how body fat is measured and what constitutes an excess level of body fat. 

How to calculate body fat

A number of methods are available to calculate what percentage of your weight is fat, all of which have pros and cons. All are estimations and therefore have margins of error. The most sophisticated methods include hydrodensitometry (underwater weighing), dual-energy X-ray absorptiometry (DXA), and air displacement plethysmography (Bod Pod). These methods are the most precise, but also the least commonly used because of their size, expense, and complexity.

The more commonly used methods are skinfold thickness testing using calipers and bioelectrical impedence analysis (BIA).

Skinfold thickness testing

This is the preferred method of many gyms and dieticians. An instrument called a caliper is used to measure skinfold thickness at various body sites on the body. Equations are used to predict body fat percentage based on these measurements. While fairly quick and easy, this technique is prone to errors if the measurements are not taken correctly or an incorrect formula is applied. The results are not as accurate or reproducible as the more sophisticated methods, especially when using the self-administered skinfold calipers.[1]  For these reasons, skinfold thickness testing, while useful, is best done be a trained professional with a lot of experience.

Bioelectrical impedance analysis

If you want to learn how to calculate body fat at home, your best bet is bioelectrical impedance analysis, the technology behind the body fat scales sold for home use. This method is also used in many gyms and clinics.

The principle behind this technique is that fat contains little water; most of the body’s water is in the lean compartment. Lean body mass conducts electricity better than fat body mass. Therefore, when an electrical current encounters fat, there is more resistance. By measuring how easily currents move through the body, body fat can be estimated. BIA equipment sends an imperceptible electric current through the body, measuring the resistance. Equations are used to estimate body fat percentage and fat-free mass.

While safe, convenient, and relatively inexpensive, BIA machines are not as accurate as other methods, particularly if you use one of the many commercially available body fat analyzers, although the technology is improving. Results may change depending on the type of BIA machine (how many electrodes are used, where the electrodes are placed), the manufacturer’s choice of equations used for prediction, your hydration status, and other factors. The most accurate commercially available body fat analyzers appear to be the models that have both handles for gripping and a scale (hand-to foot models), rather than hand-to-hand or foot-to-foot models.[2]

While BIA testing using the home models isn’t as accurate as the more sophisticated methods, it is still accurate enough to be extremely useful for getting a fairly good idea of your body fat percentage so you can track your body composition over time.

Healthy body fat percentages

After you’ve learned how to calculate body fat, how do you interpret the information? 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.[3] Above or below this level is usually considered unhealthy and could put you at risk for health problems. See the accompanying ideal body fat percentage chart for more detailed information on healthy and unhealthy body fat percentages, based on sex and age.

The importance of measuring and tracking body fat during weight loss

Unhealthy weight loss programs may help you lose weight, but at a high cost. They can result in more muscle loss than fat loss. So even though you look thinner, your body fat percentage is still too high. When too much muscle is lost and excess fat is retained, your risk of serious health concerns, including high blood pressure, high cholesterol, cardiovascular disease, insulin insensitivity, type 2 diabetes, hormone imbalance, and more, is still increased. Furthermore, losing the majority of weight from muscle rather than body fat may increase the likelihood that the little amount of fat you did lose will return—plus more. In contrast, healthy body composition programs help you lose weight and look thinner by targeting fat and preserving muscle. (Read “How to Burn Fat for Fuel” for ideas on healthy weight loss.) When you keep (or actually increase) your muscle mass while losing body fat, you reduce your risk of disease. And because a higher ratio of muscle-to-fat may increase your metabolic rate, your body may be able to more effectively burn calories each day, decreasing the likelihood that fat will return.

Being overfat is dangerous, even if your weight is normal

Another benefit of knowing how to calculate body fat is that it can provide information about your risk for many chronic diseases—information that may have otherwise gone unnoticed. It may surprise you that you can have a normal body mass index (BMI), based on your height and weight, but still be overfat based on body composition testing. Researchers call this condition “normal weight obesity.” Normal weight obesity is often defined as having a normal BMI (less than 25) but excessive body fat, which some organizations define as more than 20% for men and 30% for women, and others define as over 25% for men and 35% for women.[4,5] Americans are increasingly becoming overfat, even those of us with normal BMIs.[6] For instance, on average, fat comprises approximately 24% of body weight in males and 38% in females at age 25.[7]

Having a high percentage of body fat is not healthy, even if your weight is normal. It still puts you at increased risk of developing the myriad of chronic diseases associated with obesity, especially if the majority of your excess fat is in the abdominal region.[8]

Being overfat increases your risk for the following:

• Metabolic syndrome [9-11]
• Insulin resistance [10]
• High triglycerides [10]
• Low HDL cholesterol [10]
• High CRP (measurement of chronic inflammation) [12]
• Diabetes [13]
• High blood pressure [14]
• High blood sugar [14]
• Blood vessel inflammation [15]
• Cardiovascular disease [16,17]
• Increased physical impairment [18]
• Higher mortality [19]

How to use this information now to improve your body fat percentage and your health

1. Calculate your own body fat percentage using one of the hand-to-foot BIA machines.
2. Determine if your own body fat percentage is healthy, overfat, or obese by using the ideal body fat percentage chart shown above.
3. If needed, begin now to improve your body fat percentage with a fitness/healthy eating plan using one of the recommended eating plans.
4. Use your BIA machine to measure your progress over time – your weight loss and your improved body fat percentage. As you see that progress, you will be motivated to stick with your healthy eating plan and thus successfully improve your health and happiness.

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[2] J Sports Med Phys Fitness. 2015 Jan-Feb;55(1-2):68-75.

[3] Medscape clinical ref. Obesity.

[4] Br J Nutr. 2014 Mar 14;111(5):887-94.

[5] Am J Clin Nutr. 2012 Mar;95(3):594-602.

[6] Obesity (Silver Spring). 2010 Nov; 18(11): 10.

[7] PLoS One. 2009; 4(9): e7038.

[8] Med J Aust. 2009 Aug 17;191(4):202-8.

[9] Am J Clin Nutr. 2003 Aug;78(2):228-35.

[10] PLoS One. 2013;8(3):e60673.

[11] Diabetes Care. 2004 Sep;27(9):2222-8.

[12] Circ Cardiovasc Imaging. 2012 May 1;5(3):349-56

[13] Endocrine. 2014 Oct 14.

[14] Nutr Metab Cardiovasc Dis. 2010 Nov;20(9):669-75.

[15] Cardiovasc Diabetol. 2014; 13: 70.

[16] Am J Cardiol. 2013 Nov 15;112(10):1592-8.

[17] Obes Rev. 2002 Aug;3(3):209-15.

[18] Eur J Intern Med. 2014 Jul;25(6):517-22.

[19] Prog Cardiovasc Dis. 2014 Jan-Feb;56(4):426-33