What Is the Formula to Calculate Body Fat Percentage?

For a truly accurate measurement of your body fat percentage, you would need to go to a laboratory and have a trained professional determine it through clinical applications. This would take time and money. Fortunately, you can also get an estimate of your body fat with only a scale and a tape measure. It may not be as accurate as tests done in a clinical setting, but it can help you determine if you are within a healthy range or if you need to change your eating and exercise routine. When measured consistently over time, this formula will show you if you are losing or gaining body fat.

Your body fat percentage helps you break down the number you see on the scale into fat and lean mass. (Image: Stefanie Hafner/The Image Bank/Getty Images)

Lean Mass and Body Fat

Weight fluctuates depending on the time of day, your clothing and how hydrated you are. The number on the scale will tell you how much you weigh, but it won't break your weight down into fat and lean mass. Lean mass consists of bones, tissues, organs and muscle. Fat consists of essential and nonessential fat. Essential fat is what your body needs to function properly and any extra fat is considered nonessential. A healthy percent fat for men is between 10 and 22. A healthy percent fat for women is between 20 and 32. If your percent body fat is above the recommended range, it puts you at risk for type-2 diabetes, heart disease and certain cancers. If you don't have enough essential fat, your reproductive system may be impaired and the way your body uses vitamins may be affected.

Estimating Your Body Fat

Your body mass index is a number used to determine if you are at a healthy weight, overweight or underweight. It's also a very rough indicator of your body fat. Use an online calculator to determine your BMI, then use it to get an estimate of your body fat percentage.

A study published in the British Journal of Nutrition used the following equations to predict adult body fat percentages:

For men: (1.20 x BMI) + (0.23 x age) – 10.8 – 5.4

For women: (1.20 x BMI) + (0.23 x age) – 5.4

For example, a 5-foot, 4-inch 25-year old female weighing 120 pounds would have a BMI of 20.5 and could estimate her body fat percentage to be about 25 percent using this calculation:

(1.2 x 20.5) + (0.23 x 25) - 5.4 = 24.95

A 2013 study in BMC Public Health showed a BMI calculation that included age and gender was as effective as some clinical measurements of body fat percentage. However, it won't be as accurate as other methods -- like underwater weighing -- used to determine body fat levels.

Clinical Measurements of Body Fat

For a more accurate number, you can have your body fat measured in a clinical setting. Three common clinical methods are skinfold measurements, bioelectrical impedance analysis and BOD POD. With the first method you would get your skinfold thickness measured at different points on your body. The sum of the measurements would then be plugged into a formula to determine your body fat percentage. There is a lot of human error that can be involved with skinfold measurements, so be sure to get it done at a reputable site with trained professionals.

The BOD POD is a fiberglass unit that measures your body weight and volume. The ratio of the two is then put into a formula to determine body fat percentage. Finally, bioelectrical impedance analysis uses electrodes to see how quickly currents travel through your body. Currents travel easily through water -- found in lean mass -- but resist traveling through fat. Through that resistance, this technique is able to estimate your body fat percentage.

Dietary Changes to Lower Body Fat

If you are looking to decrease your body fat percentage, consider dietary changes. Harvard Health Publications recommends a diet rich in fruits, vegetables, whole grains and lean protein. Try chicken breast topped with mango salsa, brown rice and leafy, green vegetables for dinner.

Cut back on fatty cuts of meat and processed meats as well as trans fats found in margarine, store-bought baked goods and snack crackers. Opt instead for omega-3-rich fish and other healthy fats in moderation. Enjoy salmon or herring for dinner, snack on a handful of walnuts and cook with soybean or sunflower oil.

Cut back on high-fructose corn syrup, found in soft drinks, some desserts and other processed foods such as sweet pickles and bottled sauces. A 2015 study published in Scientific Reports concluded that processed fructose contributes to weight gain, deposition of fat and physical inactivity in the average American. Replace sugary drinks with skim milk, water and unsweetened tea. Satisfy your sweet craving with natural fructose found in fruits or plain yogurt with a teaspoon of honey rather than purchasing baked goods from the grocery store.

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