Body Fat Calculator
This body fat calculator estimates body fat percentage based on several methods, including using body mass index (BMI), relative fat mass (RFM), the US navy method, and the Jackson-Pollock skinfold method. To use the calculator, select the calculation method, provide the corresponding information, and click the "Calculate" button.
The BMI estimation method has an estimated average error of 4.66% for adults. The RFM method has an estimated average error of 4.2% for Americans. The US navy method has an estimated average error of 3-4%. The skinfold method has an estimated average error of around 3%. Overall, the more steps it takes, the more accurate the result. The BMI estimation method is the least accurate. However, it is the most convenient for most people. It provides a quick estimate of body fat percentage, which can be used as a reference for where a person stands relative to the average person.
To ensure accuracy, please measure the circumference or height to the nearest 1/4 inch or 0.5 cm. If measuring the skinfold, please take the average of 2 or more measurements.
What is body fat?
A person's body is made up of a variety of things such as fat, water, proteins, and minerals. Body fat percentage (BFP) is total fat mass divided by total body mass, multiplied by 100. Body fat percentage is one of the most accurate indicators of a person's fitness level, since it is the only measurement used that calculates a person's body composition without regard for height and weight. This is in contrast to measures such as body mass index (BMI), which makes many assumptions about a person's body composition solely based on height and weight; it is mostly useful as a comparison of body fat percentage in people of different heights and weights.
Essential vs. storage fat:
There are a number of different types of fat, but they can be broadly categorized as essential fat or storage fat.
Essential fat is fat that is necessary in order for the body to function normally. It is found in parts of the body such as the heart, bone marrow, lungs, liver, spleen, and more. Women need more essential fat than men for reasons related to child bearing. Generally, the minimum amount of body fat a woman needs is 12%, while men need 3%. Body fat percentages below these levels is unhealthy and can lead to the body being incapable of carrying out necessary processes and functions; examples include slow wound healing, hair loss, frequent sickness, and more.
Any fat above ~3% for men or ~12% for women is referred to as storage fat, or nonessential fat. Storage fat is good in appropriate amounts, but excess fat that leads to overweight and obesity has detrimental health effects. The generally accepted overall range of fat for good health for men, including essential and storage fat, is 10-22%; for women, it is 20-32%. People who remain within these ranges are at lower risk for developing health effects such as obesity, diabetes, high blood pressure, and certain cancers.
Storage fat on the other hand, is fat that accumulates in adipose tissue, that is stored for use in case of emergencies such as starvation or severe caloric deprivation. While some degree of storage fat is necessary, excess levels of storage fat is almost universally considered to have negative health impacts, particularly when concentrated around the abdomen.
Storage fat can be found all over the body. For example, storage fat around internal organs and abdomen is referred to as visceral fat, while storage fat under the skin is referred to as subcutaneous fat. Storage fat can also be found between muscles and almost anywhere else in the body.
Although most types of storage fat can be categorized varying degrees of good or bad, visceral fat is largely considered to be bad fat that should ideally be avoided. Visceral fat has been shown to generally increase with age, and has been linked to a number of adverse effects such as increased risk of breast cancer and colorectal cancer, stroke, type 2 diabetes, dementia and Alzheimer's disease. A large factor affecting visceral fat is diet. Heavily processed foods are laden with large amounts of sugar and/or saturated fats and trans fats (cookies, sugary drinks, candy, etc.), and contribute significantly to visceral fat. While some levels of saturated fats can be good, trans fats in foods should largely be avoided whenever possible. Regular exercise, as well as consuming healthier foods such as lean proteins, whole grains, beans, fish, and eggs in moderation can help decrease visceral fat.
How to measure body fat?
There are many different methods used to measure body fat. The methods used by this calculator include use of body mass index (BMI), relative fat mass (RFM), and the US Navy circumference and Jackson-Pollock skinfold methods in conjunction with the Siri formula.
Body mass index (BMI) is a measure that is used to categorize a person's weight, be it underweight, healthy weight, overweight, or obese. It is a useful screening measure but it is not necessarily indicative of the body fatness or health of an individual. It is frequently used because the only measurements needed are the height and weight of the individual. Once height and weight are measured, BMI can be calculated as:
BMI is, by itself, not a measure of body fat. However, it is correlated with other more direct measures of body fat. Studies have been done to create equations that estimate body fat percentage using BMI:
|BF% =||-44.988 + (0.503×age) + (10.689×sex) + (3.172×BMI) - (0.026×BMI2) + (0.181×BMI×sex) - (0.02×BMI×age) - (0.005×BMI2×sex) + (0.00021×BMI2×age)|
where age is age in years, sex is 0 for males and 1 for females, and BMI is the person's body mass index.
BF% = 1.51×BMI - 0.70×age - 3.6×sex + 14
where age is age in years, sex is 0 for males and 1 for females, and BMI is the child's body mass index.
Using BMI to estimate body fat percentage is one of the easiest methods, since it only requires the height, weight, and sex of a person for the calculation. However, it is one of the least accurate measures since BMI cannot account for a person's body composition, which significantly affects a person's body fat percentage.
Relative fat mass (RFM) refers to an equation developed to more accurately (than BMI) estimate whole-body fat percentage using height, waist circumference, and sex. The study compared many different measurements (arm and leg lengths, waist, calf, arm and thigh circumferences, triceps, weight, height, etc.) and their correlation to whole body fat percentage and found height and waist circumference to be the most indicative of whole-body fat percentage. To validate the accuracy of the developed equation, the body fat percentages of participants were also measured using dual energy X-ray absorptiometry, one of the most accurate measures of body fat percentage. The developed equation, named RFM (which measures body fat percentage), is as follows:
BF% = 64 - (20 × height/waist circumference) + (12 × sex),
where sex = 0 for men and sex = 1 for women.
It is worth noting that measurement of waist circumference is not standardized. For the study that developed the equation, waist circumference was measured using measuring tape around the unclothed waist of participants in a horizontal plane at the level of the upper part of the pelvis, while the participant was standing, and after they exhaled.
U.S. Navy Method
The U.S. Navy circumference method is a measure of body density based on a person's height and neck circumference. It is not a direct measurement of body fat percentage. Once body density is determined, it can be used with a second equation, the Siri equation (described below) to find the estimated body fat percentage. Below are the formulas for body density for both men and women (using SI units):
Body density = 1.29579 - 0.35004×log10(waist + hip - neck) + 0.22100×log10(height)
Body density = 1.0324 - 0.19077×log10(waist - neck) + 0.15456×log10(height)
To measure waist circumference, measure the person's waist at a horizontal level around the navel for men, and around the smallest width for women. The person should ideally exhale completely, but not pull their stomachs inwards. To measure the neck, start just below the larynx, and measure the circumference. To measure hips, measure the circumference at the largest horizontal measure.
Once body density is determined, it can be plugged into the Siri equation to find body fat percentage:
Jackson-Pollock skinfold method
There are a number of skinfold methods used to measure body density, which can in turn be used with the Siri equation to estimate body fat percentage. These skinfold methods make use of a skinfold test, also referred to as a pinch test. In a skinfold test, calipers are used to precisely measure a pinch of skin at a number of different, standardized sites on the body. The thickness of these skinfolds is a measure of the subcutaneous layer of fat. Once the thickness has been measured, various equations can be used to estimate body fat percentage. The methods described below differ in the number of sites measured, where the number of sites measured does not necessarily improve the accuracy of the result. Rather, the accuracy of the result is based more on each person's unique body fat distribution. Thus, the specific method and equations used should be selected based on which sites can be most consistently and precisely measured for a given individual.
The 4 sites involved in the 4-site skinfold test are the triceps, thigh, abdomen, and the suprailiac. The triceps should be measured at the back of the upper arm; thighs should be measured in the middle of the upper thigh; abdomen should be measured next to the belly button; suprailiac should be measured above the front forward protrusion of the hip bone. The formula used are shown below, where thickness is measured in millimeters (mm):
BF% = (0.29669 × sum of skinfolds) - (0.00043 × (the sum of skinfolds)2) + (0.02963 × age) + 1.4072
BF% = (0.29288 × sum of skinfolds) - (0.0005 × (sum of skinfolds)2) + (0.15845 × age) - 5.76377
The 3 sites involved in the 3-site skinfold test are the triceps, chest, and subscapular skinfolds. The triceps should be measured at the back of the upper arm; chest should be measured in the middle of the chest, near the armpit; subscapular should be measured just below the edge of the shoulder blade. The formulas used are shown below, where thickness of the skinfold is measured in millimeters (mm):
Body Density = 1.0994921 - (0.0009929 × sum of skinfolds) + (0.0000023 × (sum of skinfolds)2) - (0.0001392 × age)
Body Density = 1.1125025 - (0.0013125 × sum of skinfolds) + (0.0000055 × (sum of skinfolds)2) - (0.000244 × age)
The 7 sites involved in the 7-site skinfold test are the chest, axilla, triceps, subscapular, abdomen, suprailiac, and thigh. The chest should be measured in the middle of the chest, near the armpit; the axilla should be measured at the midline of the side of the torso; the triceps should be measured at the back of the upper arm; the subscapular should be measured just below the edge of the shoulder blade; the abdomen should be measured next to the belly button; the suprailiac should be measured above the front forward protrusion of the hip bone; the thigh should be measured in the middle of the upper thigh. The formulas for the 7-site skinfold test are shown below, where thickness is measured in millimeters (mm):
Body Density = 1.097 - (0.00046971 × sum of skinfolds) + (0.00000056 × (sum of skinfolds)2) - (0.00012828 × age)
Body Density = 1.112 - (0.00043499 × sum of skinfolds) + (0.00000055 × (sum of skinfolds)2) - (0.00028826 × age)
Using the Siri Equation
The Siri equation is one of a number of equations that estimates body fat percentage based on body density. Many methods, such as the skinfold method and US navy method mentioned above, calculate body density. For this reason, the Siri equation, as well as others such as the Brozek equation, were developed. Once body density is known, the Siri equation can then be used to estimate body fat percentage using the following formula:
The Siri equation is based on the model of the human body as being comprised of two compartments: fat mass and fat-free mass. The densities of fat mass and fat-free mass have been experimentally determined, so the Siri equation estimates a person's body density using the density formula, density = mass/volume by substituting volume with mass/density.