Lean Body Mass Calculator

Use this calculator to estimate your lean body mass (LBM), more correctly called fat-free body mass (FFM).

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How to measure neck, waist and hip circumference?

Our lean body mass calculator (more correctly called fat-free body mass calculator) works by using four of your measurements: height, neck, waist, and hips, your age and gender, to estimate the percentage and mass of fat in your body. It then subtracts that from 100% to arrive at the lean body mass (LBM) estimate. Here is some advice on taking these measurements with the help of 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 record the measures in centimeters or feet and inches, since our LBM calculator supports both units. Measuring to the nearest half inch or within 1 cm should be sufficient.

Estimating Lean Body Mass (LBM)

To estimate the lean body mass, we use the U.S. Navy Method Body fat formula and then subtract the fat percent from the total mass to produce a lean body mass estimate. The body fat percent formulas used are as follow.

For men, imperial metrics (inches), the formula is [3]:

86.01 x log10(waist - neck) - 70.041 x log10(height) + 36.76

For women, imperial metrics (inches), the formula is [4]:

163.205 x log10(waist + hip - neck) - 97.684 x log10(height) - 78.387

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)

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.

Fat-Free Body Mass vs Lean Body Mass

It should be noted that lean body mass (LBM) is not the same as fat-free body mass (FFM). LBM is a theoretical percentage of non-sex-specific essential fat that is about 4-7% of the total body mass. That fat is mostly contained in the central nervous system, bone marrow, and internal organs. FFM on the other hand is the body mass devoid of all extractable (non-essential) fat, so FFM = Body Mass - Fat mass. Fat-free body mass is typically 80-90% of the total, reaching 95% in some athletes.

There are standards for leanness. The minimal lean body mass for the reference man (61.7 kg) includes 3% of essential body fat. Marathon runners can go down to 1% body fat. For women the lower limit for the reference woman equals about 12% essential fat. Even the leanest women rarely fall below 10-12% body fat.

Methods for measuring lean body mass

While this online lean body mass calculator is a good tool, it is not perfect. Its advantage is that it is very easy to use and decently accurate. Other, more expensive and more accurate methods are available, such as DEXA (Dual-Energy X-ray Absorptiometry), CT and MRI scans (so-called 3D scans), body density (underwater weighing). The most popular of these is DEXA, as it is accessible, easy to perform and reliable.

Other less precise methods are bioelectric impedance analysis, total body water measurement, total body counting, and neutron activation. They have accuracy issues, especially in overweight or obese individuals, and even for individuals with normal weight due to some of their assumptions being too general.


[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

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., "Lean Body Mass Calculator", [online] Available at: https://www.gigacalculator.com/calculators/lean-body-mass-calculator.php URL [Accessed Date: 31 Mar, 2020].