Body Fat Calculator

Use this calculator to estimate your body fat percent based on population averages. It also shows your body fat category, as well as the ideal percentage of fat for your age range.

Share calculator:

Put it on your site!
get code

How to measure neck, waist and hip circumference

Our body fat calculator needs four of your measurements: height, neck, waist, and hips, to determine the percentage and mass of body fat. Here is how to take the measurements, using a soft measurement tape:

  • Height: step on a flat surface that is perpendicular to a wall, column or a door frame. Look straight ahead. Get an assistant to place a ruler or another straight object on the top of your head so it is horizontal and mark the point at which it touches the wall, column, etc. Step out and measure the height from that point to the floor.
  • Neck: measure just inferior to the larynx with sloping slightly downward to the front (narrowest point).
  • Waist: measure at the widest point of the abdomen, at the level of your naval (umbilicus).
  • Hips: measure your hips at the widest point below your waist, while keeping your feet together for an accurate measurement.

You can use both centimeters and inches to record the measurement, since our body fat calculator supports both units. Accuracy to the nearest half inch or within 1 cm should be sufficient.

It is recommended that you wear minimal clothing during the measurement. It is also recommended to have your measures taken by an assistant, since if you are taking them yourself you will not be fully relaxed and may be twisting your body and skewing the results.

Body fat formula (U.S. Navy Method)

In calculating body fat, we use the method developed for the United States Navy Force in the second half of the 20-th century. The standard error of the estimate is ~3.5 percent points in either direction [2], meaning that about 68% of estimated body fat percentages will fall within ±3.5 of the true BFP, while ~95% of estimated BFPs will fall within ±7 of it.

For men, SI metrics (centimeters), the formula is [3]:

100 x ((4.95 / (1.0324 - 0.19077 * log10(waist - neck) + 0.15456 * log10(height))) - 4.5)

For women, SI metrics (centimeters), the formula is [4]:

100 x ((4.95 / (1.29579 - 0.35004 * log10(waist + hip - neck) + 0.22100 * log10(height))) - 4.5)

For imperial metrics (inches) high-precision conversions are performed automatically by our body fat percentage calculator.

Is my body fat percentage normal?

The American Council on Exercise Body Fat Categorization is presented in the table below:

Body Fat Categorization
Essential fat 10-13% 2-5%
Athletes 14-20% 6-13%
Fitness 21-24% 14-17%
Average 25-31% 18-25%
Obese 32%+ 25%+

The above are, of course, averages, so the normal body fat percentage may vary depending on your health condition, level and type of physical activity, and others.

How to reduce body fat?

OK, so you've used our body fat calculator and the results were not great, so you are looking to improve them. But where does one start? There are several general tips you can follow to help reduce your body fat percentage.

First and foremost, you should consider the number of calories you eat. Our calorie calculator will help with that. It is not an easy task to accomplish as it requires significant persistence and measured steps, but especially with the help of people around you and strong motivation, it is doable.

Second, you can alter the macronutrient composition of your diet, in other words the proportions of fat (lipids), carbs (carbohydrates) and proteins you consume through food. Our macronutrient calculator can be of assistance, but with regards to fats it should be noted that the same amount (mass) of food rich in fats is about 2 times more caloric than equivalent amounts of carbs or proteins.

Third, exercise, resistance training in particular. As Katch et al. write [1], you can eat more yet weigh less by regular exercise, which allows a person to maintain lower percentage of body fat even despite age-related tendency toward weight gain that begins at the age of 21 and continues at a rate of 1 lbs per year until 60. Physically active persons maintain a lighter and leaner body and a healthier health risk profile despite increased caloric intake.

If you are an athlete, weight loss and fat loss should preferably take place during off-season or at least begin before the competitive seasons and under advice from a qualified sports dietitian.

Contrary to popular belief which comes from amino acid infusion in deficient patients, consumption of amino acid supplements does not decrease body fat. Research on healthy subjects does not provide evidence in support of generalized use of such supplements with the aim of fat loss, muscle growth, etc. and this includes supplements of arginine, lysine, ornithine, tyrosine, and other amino acids, regardless of combination. No physical performance improvements were detected, either [1].

You may want to consider replacing sugar-sweetened beverages and milk with water, as well as drinking significant amounts of water over the recommended daily water intake as there is some evidence that this might help in reducing the energy intake and can lead to weight loss. Our water calculator can assist in that task.

Methods for measuring body fat

Even though using an online body fat calculator like ours is a decent method to estimate your body fat percentage, it is not the most accurate. Other, usually more involved and more expensive methods often produce superior results. None of them can be described as "the best method to measure body fat" - all have advantages and drawbacks [5]. Here are some of them in brief.

Bioelectric Impedance Analysis

This is the only indirect method other than the one using body measurements and weight such as in our body fat calculator. It works since fat conducts electricity differently than bones and muscle tissue - it has different impedance. This is due to the lower water percentage (~50%) in fat, compared to muscle (75%). The measurements consists of placing electrodes on precisely defined parts of the body, running a small electrical current through them and measuring the resistance between the different points.

The pros of the bio-impedance method are that it is cheap and easy to do. On the negative side, their accuracy is highly suspect, even for healthy, non-obese individuals, but for overweight and obese persons it is very questionable. The large error in individual measurement limits their use in clinical environments.

Body Fat via Total Body Water

This is a "direct method" for body fat measurement and it is easy to perform as it doesn't require any real participation on your side. Measured water/isotope dilution volumes allow prediction of fat free mass and fat percentage in normal weight individuals, but are of questionable value for overweight and obese ones, due to the assumption about an average proportion of total body volume of 73%. This proportion, however, ranges from 67-80%, and some of it is present in extracellular fluid (15-30%) and it increases with the degree of adiposity. Disease and other conditions, associated with obesity further affect the accuracy of the measurement.

Total Body Counting and Neutron Activation

These are two other direct methods. Total body counting measures the amounts of potassium 40 (40K) in the body, which is possible as it is naturally radioactive and has a known half-life. It is found in nearly all life cells, so it is a good estimate. However, there are very few such detectors in operation in the U.S.

Neutron activation methods are reportedly very accurate for tissue-specific body composition, but take about an hour to complete for the whole body. The technique is quite advanced, involving exposure to a neutron field and measuring of gamma input as the cell nucleus relaxes to its pre-exposed state. This body fat measuring technique is also used to measure elements such as carbon, nitrogen, sodium, and calcium in the body.

As you might have guessed, the significant levels of neutron exposure is what makes this highly accurate technique not suitable for large-scale use.

Body Density (Underwater Weighing)

Hidrodensitometry, or underwater weighing is a method based on measurement of body weight, body volume and residual lung volume. The method is quite accurate, but has its limitations, most notably its reliance on the subject's performance. Children or very obese people might have trouble fully submerging under water and holding their breath.

Another method relies on air displacement, instead of water displacement: air displacement plethysmography. The advantage is that there is no need to hold your breath, but it still makes assumptions about tissue density that might have a higher than expected error in certain individuals looking to calculate their body fat percentage.

Dual-Energy X-ray Absorptiometry

Also called DEXA, it is the most popular and quite convenient method for quantifying the amount of body fat and involves being subjected to two low-energy level X-rays running through your body. A typical scan takes 10-20 mins and exposes you to less than 5 mrem of radiation. Mathematical algorithms then separate the body tissues using physical and biological models. It, too, has its assumptions about levels of hydration, potassium content, and tissue density.

On the negative side, there are some physical limitations of body weight, length, thickness and width, and the type of DXA machine used: pencil or fan beam. Most obese adults and even some children are too wide, thick or heavy to receive a whole-body scan. Another issue is that even the dual-energy X-ray method might be inaccurate for extreme populations due to lack of testing and stretching of the inherent assumptions.

CT and MRI

Computer Tomography (CT) and Magnetic Resonance Imaging (MRI) are also used to estimate body fat, but they suffer from some issues. CT can handle very obese patients, but is inappropriate for whole-body scans due to the radiation levels involved. MRIs are often not big enough to accommodate large body sizes. On the plus side, CT can assess nonadipose fat - the fatty infiltration of skeletal muscle or liver tissue, which play a substantial role in the development of insulin resistance as in type II diabetes.


[1] Katch V.L., McArdle W.D., Katch F.I (2011) "Essentials of Exercise Physiology", fourth edition

[2] Hodgdon J.A. (1990) "Body Composition In The Military Services: Standards And Methods", Body Composition and Physical Performance, National Academies Press (US)

[3] Hodgdon J.A., Beckett M.B. (1984) "Prediction of percent body fat for U.S. Navy men from body circumferences and height." Report No. 84-11, Naval Health Research Center, San Diego, CA

[4] Hodgdon J.A., Beckett M.B. (1984) "Prediction of percent body fat for U.S. Navy women from body circumferences and height." Report No. 84-29, Naval Health Research Center, San Diego, CA

[5] Duren D.L., Sherwood R.J., Czerwinski S.A., et al. (2008) "Body Composition Methods: Comparisons and Interpretation", Journal of diabetes science and technology 2(6):1139-1146.

Cite this calculator & page

If you'd like to cite this online calculator resource and information as provided on the page, you can use the following citation:
Georgiev G.Z., "Body Fat Calculator", [online] Available at: URL [Accessed Date: 18 Jul, 2018].