Lean Body Mass Calculator 💪

1. How to calculate Lean Body Mass (LBM)
2. Lean body mass reference standards
3. Fat-Free Body Mass vs Lean Body Mass
4. Muscle Mass vs Lean Body Mass
5. Methods for measuring lean body mass
6. How to measure neck, waist and hip circumference?

    How to calculate Lean Body Mass (LBM)

To estimate the lean body mass (a.k.a. lean body weight, LBW), the calculator uses the U.S. Navy Method Body fat formula and then subtracts the fat percent from the total mass to produce the final estimate. The body fat percent formulas used are as follows.

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)

Note the instructions on obtaining accurate measurements. In calculating lean body mass with these equations 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. These error bounds on the estimate have to be taken into account when using the calculation results for the amount of muscle, ligaments and essential fat which constitutes the lean body mass.

The lean body mass calculator also outputs the lean mass index (LMI) in kg per meter squared (kg/m^-2) which is a measure similar to BMI but for lean mass instead of total body mass. The inputs can be weight pounds or kilograms for the total body weight, and feet and inches, centimeters or meters for body height. The age is in years.

    Lean body mass reference standards

There are standards for leanness derived from scientific studies of certain populations. 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.

Reference values using lean mass index as a measure of lean body mass standardized for height are most useful in practice. A set of such values are provided in the tables below. Note that a bigger LMI means a leaner body. A larger lean body mass naturally translates mostly to more muscle per unit of body weight and also to a smaller body fat percentage. Additionally, our lean mass calculator automatically calculates and outputs the reference percentile by using a more precise version of these tables.

Lean body mass index reference values for Caucasian men:

LMI percentiles per age group, men

Age group / LMI Percentile	20-th percentile	50-th percentile	80-th percentile
20-39 years	17.7	19.4	21.8
40-59 years	17.3	19.0	21.8
60-79 years	17.0	18.0	20.6

Lean body mass index reference values for Caucasian women:

LMI percentiles per age group, women

Age group / LMI Percentile	20-th percentile	50-th percentile	80-th percentile
20-39 years	14.0	15.4	17.2
40-59 years	13.9	15.4	17.3
60-79 years	13.9	15.1	16.9

Values in the tables are adopted with some grouping and averaging from Table 3 of "Reference standards for lean mass measures using GE dual energy x-ray absorptiometry in Caucasian adults" ^[5] and apply to Caucasians only. It should also be mentioned that DXA estimates are more accurate than estimates produced using body measurements so the table should be used as a rough guide only.

    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), although the terms may sometimes be used interchangeably. LBM is a theoretical percentage which includes both non-fat tissue (bones, muscles, ligaments, etc.), but also some non-sex-specific essential fat which is up to 3-4% of the total body mass for men and up to 5-7% for women ^[1]. That essential 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 fat, including essential fats. FFM = Body Mass - Fat mass. Fat-free body mass is typically 80-90% of the total, reaching 95% in some athletes.

    Muscle Mass vs Lean Body Mass

Lean body mass is also not equivalent to muscle mass, though sometimes this is mistakenly believed. LBM includes different non-fat tissues like bones, ligaments, and muscles^[1]. So, while it does contain muscle mass, the lean body weight also contains a substantial proportion of other body parts so using it interchangeably with muscle mass is, strictly speaking, incorrect. In everyday speech some may use "muscle mass" to mean "lean body mass" and that is totally fine given all participants understand what is meant.

    Methods for measuring lean body mass

While this online lean body weight 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, a.k.a. DXA), 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 for calculating lean body weight 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.

    How to measure neck, waist and hip circumference?

Our lean body mass calculator (a.k.a. fat-free body mass calculator) works by using four body measurements: height, neck, waist, and hips, 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 for accurate estimate of how much muscle and other non-fat tissue there is in your body as well as the percentage of muscle from your total body weight.

* Note percentiles are standard for Caucasians only, due to the limited data available. Reference standards based on reference [5] below.