Lean body mass (LBM) is everything in your body that isn't fat: muscle, bone, organs and water. If you know your body fat percentage, LBM = weight × (1 − body fat %). Without it, the Boer formula estimates LBM from height and weight. A 35-year-old woman at 5′5″ and 165 lb has an estimated LBM of about 107 lb (48.7 kg) by Boer.
Key takeaways
- LBM equals total weight minus fat mass, and it includes organs, bone and water as well as muscle.
- The Boer, James and Hume formulas estimate LBM from height and weight alone, but they cannot see your actual body composition.
- If you have a body-fat estimate, using it is usually more individual than a height-and-weight formula, but only as accurate as that estimate.
- LBM feeds directly into the Katch–McArdle and Cunningham resting-energy equations and into protein targets.
How does this lean body mass calculator work?
Enter your sex, weight and height, and optionally your body fat percentage. The calculator uses the Boer formula as its headline estimate, lists Boer, James and Hume side by side, and shows the fat mass and body fat percentage implied by Boer.
If you add a body fat percentage, the calculator also computes LBM directly from it, puts that row first and uses it as the headline figure. It then shows your Katch–McArdle BMR from the headline LBM.
What are the lean body mass formulas?
All three formulas use height and weight and have different constants for men and women (Boer, 1984; Hume, 1966).
Men: LBM (kg) = 0.407 × weight(kg) + 0.267 × height(cm) − 19.2 Women: LBM (kg) = 0.252 × weight(kg) + 0.473 × height(cm) − 48.3
LBM = weight × (1 − body fat % ÷ 100) fat mass = weight − LBM
The James formula adds a squared weight-to-height term, and Hume uses a linear equation like Boer’s with different constants.
Worked example
A 35-year-old woman who is 5′5″ (165 cm) and weighs 165 lb (74.8 kg).
| Method | Lean body mass | Implied body fat |
|---|---|---|
| Boer | 107 lb (48.7 kg) | 35.0% |
| James | 109 lb (49.7 kg) | 33.6% |
| Hume | 106 lb (47.9 kg) | 36.0% |
| From 30% body fat | 115.5 lb (52.4 kg) | 30.0% |
The three formulas agree within about 4 lb. The body-fat method differs because it uses a measurement of her actual composition rather than an average for her height and weight.
For comparison, a 30-year-old man at 5′10″ (178 cm) and 190 lb (86.2 kg) has a Boer LBM of 140 lb (63.3 kg), James 143 lb (64.7 kg) and Hume 130 lb (59.1 kg). The formulas diverge more for him, a reminder that these are estimates.
Why does lean body mass matter?
LBM is the main driver of resting energy use. Katch–McArdle puts BMR at 370 + 21.6 × LBM in kg (McArdle, Katch & Katch), and Cunningham uses 500 + 22 × LBM (Cunningham, 1980). Using the Boer LBM above, the example woman’s Katch–McArdle BMR is about 1,421 kcal. With the 30% body-fat figure it is about 1,502 kcal. Compare with the BMR calculator, which shows all equations together.
LBM also helps with protein targets. If you carry a lot of body fat, setting protein from lean mass or goal weight avoids overshooting. See the protein calculator.
How can I measure lean body mass directly?
Formulas estimate. Measurement tools include DEXA scans, bioelectrical impedance scales, skinfold calipers and the circumference-based method in the body fat calculator. Each has an error range, and results from different methods are not interchangeable, so compare like with like over time.
Does lean body mass equal muscle?
No. A large share of LBM is organs, bone and water, which don’t change much with training. Gaining muscle raises LBM, but the change is small relative to the total, and water shifts can move LBM readings by a pound or two within a day. Look at trends across weeks, not single readings.
If you want to lose fat while holding on to lean mass, see the body recomposition calculator.
Frequently asked questions
What is lean body mass?
Lean body mass is your total weight minus the weight of body fat. It includes muscle, bone, organs, connective tissue and body water. It is not the same as muscle mass, which is only one part of it.
How do I calculate lean body mass?
With a body fat percentage, multiply weight by (1 − body fat ÷ 100). Without one, use a height-and-weight formula such as Boer. For example, 165 lb at 30% body fat gives 165 × 0.70 = 115.5 lb of LBM.
Which lean body mass formula is most accurate?
They are all estimates. Boer, James and Hume agree within a few pounds for most people, and none measures composition directly. The best estimate comes from a body-fat measurement such as a DEXA scan, which the formulas can only approximate.
Is lean body mass the same as fat-free mass?
In everyday use the terms are interchangeable. Technically, fat-free mass excludes all fat while lean body mass is sometimes defined to include a small amount of essential fat, but calculators like this one treat them as the same.
How does lean body mass affect my calories?
More lean mass means higher resting energy use. Katch–McArdle estimates BMR as 370 + 21.6 × LBM (kg), so an extra 10 lb (4.5 kg) of lean mass adds roughly 98 kcal per day to the estimate.
References
- Boer P (1984). Estimated lean body mass as an index for normalization of body fluid volumes in humans. American Journal of Physiology–Renal Physiology 247(4):F632–F636.
- Hume R (1966). Prediction of lean body mass from height and weight. Journal of Clinical Pathology 19(4):389–391.
- McArdle WD, Katch FI, Katch VL (2015). Exercise Physiology: Nutrition, Energy, and Human Performance (8th ed.). Wolters Kluwer Health.
- Cunningham JJ (1980). A reanalysis of the factors influencing basal metabolic rate in normal adults. American Journal of Clinical Nutrition 33(11):2372–2374.