Lean Body Mass Calculator
- James
- 129.0 lbs (81%)
- Hume
- 120.4 lbs (75%)
Details
| Formula | Lean Body Mass | Body Fat |
|---|---|---|
| Boer | 127.4 lbs (80%) | 20% |
| James | 129.0 lbs (81%) | 19% |
| Hume | 120.4 lbs (75%) | 25% |
This lean body mass calculator estimates how much of your weight is not body fat, using three published adult formulas or a pediatric formula for children 14 and younger.
Lean body mass (LBM) is everything in the body except fat: muscle, bone, organs, skin, blood and body water. It is found by subtracting fat mass from total weight. In most adults, LBM makes up somewhere between about 60% and 90% of body weight, and men typically have a higher proportion than women.
LBM is mostly used in medicine. Doses of some drugs, especially anesthetics and other water-soluble medicines that do not distribute into fat, are calculated from lean mass rather than total weight, and some physiological tests are normalized to it. For everyday fitness goals, people more often track body fat percentage, which is simply the complement of the LBM share. Because measuring body composition directly requires equipment such as DEXA scanning or underwater weighing, researchers have developed estimating equations (eLBM) based on height and weight; the calculator shows the results of several.
Lean Body Mass Formulas for Adults
Each formula below was fitted to measurements from a particular group of adults, so they give somewhat different answers. In all of them W is weight in kilograms and H is height in centimeters. For a 5-foot-10-inch, 160-pound man, the Boer, James and Hume formulas give about 127, 129 and 120 pounds.
| Formula | Men | Women |
|---|---|---|
| Boer (1984) | 0.407W + 0.267H − 19.2 | 0.252W + 0.473H − 48.3 |
| James (1976) | 1.1W − 128 × (W/H)² | 1.07W − 148 × (W/H)² |
| Hume (1966) | 0.32810W + 0.33929H − 29.5336 | 0.29569W + 0.41813H − 43.2933 |
Lean Body Mass Formula for Children
Adult equations do not suit children, whose proportions change rapidly with growth. For children aged 14 and younger the calculator uses the Peters formula (2011), which first estimates extracellular volume (eECV) and then scales it to lean mass. It was developed to help dose medicines in children.
eECV = 0.0215 × W^0.6469 × H^0.7236, and eLBM = 3.8 × eECV, with W in kilograms and H in centimeters.
Lean Body Mass vs. Fat Free Mass
The two terms are often treated as the same thing, and for most practical purposes the difference is small. Strictly, fat-free mass (FFM) excludes all fat, while lean body mass includes the small amount of essential fat found in bone marrow, the nervous system and internal organs. That essential fat amounts to roughly 3% of body weight in men and somewhat more in women, so LBM is slightly larger than FFM.
Both measures are useful for tracking changes in body composition. During weight loss, the goal is to lose fat while keeping as much lean mass as possible, since muscle supports strength, mobility and metabolic health. Eating enough protein and doing resistance training are the best-supported ways to protect it. With age, lean mass tends to decline, a process that can lead to sarcopenia; staying active slows it.
Estimating equations work reasonably for people of average build but can be off for very muscular or very heavy individuals. For a direct measurement, DEXA scans, bioelectrical impedance devices, skinfold calipers and hydrostatic weighing are the main options, with DEXA generally considered the most accurate widely available method.
Frequently asked questions
What is a normal lean body mass percentage?
Typically about 60% to 90% of body weight. Men usually fall around 75% to 90% and women around 65% to 80%.
How is lean body mass calculated?
Directly, as total weight minus fat mass. Without a body fat measurement, formulas such as Boer, James or Hume estimate it from height, weight and sex.
Which LBM formula is most accurate?
Studies often favor Boer for adults of normal build. James can produce odd results at high body weights. Results within a few pounds of each other are typical.
Is lean body mass the same as muscle mass?
No. Muscle is only part of lean mass, which also includes bones, organs, skin, blood and water.
What is the Boer formula for lean body mass?
With weight (W) in kilograms and height (H) in centimeters, Boer gives LBM = 0.407W + 0.267H − 19.2 for men and 0.252W + 0.473H − 48.3 for women. A man who is 5 feet 10 inches (177.8 cm) and 160 pounds (72.6 kg) gets 0.407 × 72.6 + 0.267 × 177.8 − 19.2 ≈ 57.8 kg, or about 127 pounds. That is roughly 80% of his weight, implying about 20% body fat.
Results are estimates for educational purposes and are not medical advice. Talk to a doctor or other qualified health professional about your situation.
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