Compute your LBM, fat mass, and Fat-Free Mass Index (FFMI) using Boer, Hume, and James equations. Keep track of your true muscle retention goals.
A weightlifter undergoing a fat loss diet monitors their LBM to verify they are losing body fat rather than metabolically active skeletal muscle. Scale weight drops during calorie restriction, but verifying that the loss represents adipose tissue is key to maintaining strength and basic physical capabilities.
Lean Body Mass (LBM) represents the weight of your body excluding all fat tissue. LBM consists of skeletal muscle tissue, internal organs, bone structure, skin, tendons, and blood volume. Because fat tissue has low metabolic activity, LBM serves as the primary driver of baseline energy requirements and physical power generation.
This calculator implements three classic mathematical formulas to estimate lean mass from height and weight variables. These equations serve as highly reliable indicators in clinical settings when skinfold measurements are unavailable.
Developed in 1984, the Boer formula is widely regarded as one of the most reliable and consistent LBM estimations for clinical use.
// Men
LBM = 0.407 × weight (kg) + 0.267 × height (cm) - 19.2
// Women
LBM = 0.252 × weight (kg) + 0.473 × height (cm) - 48.3Developed in 1966 by Hume, this equation correlates closely with the Boer formula and is widely used for pharmacokinetics and dosage estimations.
// Men
LBM = 0.32810 × weight (kg) + 0.33929 × height (cm) - 29.5336
// Women
LBM = 0.29569 × weight (kg) + 0.41813 × height (cm) - 43.2933The James formula is also common, though it can sometimes underestimate lean mass in individuals with high levels of obesity.
// Men
LBM = 1.1 × weight (kg) - 128 × (weight (kg) / height (cm))²
// Women
LBM = 1.07 × weight (kg) - 148 × (weight (kg) / height (cm))²FFMI represents an alternative to BMI that accounts for muscularity. It divides your lean mass in kilograms by the square of your height in meters. A normalized version corrects for height differences in taller individuals, allowing comparison against general standards.
FFMI = LBM (kg) / height (m)²
Normalized FFMI = FFMI + 6.1 × (1.8 - height (m))FFMI values for men generally fall into these classifications:
In medical contexts, estimating lean body mass is crucial for calculating medication dosages (particularly anesthetics and chemotherapeutics) because fat tissue processes chemicals differently than active lean tissue. In athletic contexts, LBM helps track strength gains, structure daily protein targets (usually 1.6 to 2.2 grams per kilogram of LBM), and avoid the loss of functional muscle mass during weight cuts.
The calculations convert imperial units to metric (1 inch = 2.54 cm, 1 lb = 0.453592 kg) before applying the Boer, Hume, and James equations. FFMI calculations use the calculated LBM from the selected active formula tab.
For most practical fitness purposes, Lean Body Mass and Fat-Free Mass are used interchangeably. Technically, FFM excludes 100% of all lipids, whereas LBM includes a tiny fraction of essential lipids located in cell membranes and central nervous system tissues.
Yes. This is known as body recomposition. It is typically achieved by beginners, individuals returning from a training layoff, or people carrying significant storage fat, by combining resistance training with a high-protein diet near maintenance calories.
The equations were derived from different historical sample populations and statistical regression lines. The Boer and Hume formulas generally align very closely, while the James formula is more sensitive to extreme weight-to-height ratios.
BMI Calculator — Standard weight-to-height screen without body composition variables.
Body Fat Calculator — Estimates body fat using circumference ratios.
Ideal Weight Calculator — Estimates target body weight limits based on height.