Lean Body Mass Calculator: Boer, James and Hume Formulas
Estimate your lean body mass from three published formulas, or from your own body fat percentage for the most personal number.
TL;DR
Lean body mass (LBM) is your total body weight minus fat: everything else, muscle, bone, organs and water. This lean body mass calculator estimates it three ways, the Boer, James and Hume formulas, from just your height and weight, plus a fourth estimate if you know your body fat percentage.
Optional. Add it for a fourth, more personal estimate based on your own leanness.
Lean body mass (Boer)
137.6 lb
74% of your body weight
Boer
137.6 lb
James
140.6 lb
Hume
128.6 lb
Fat mass: 47.4 lb
See Your Lean Mass Change Over Time
PR Streak tracks your body weight, body fat and 11 body measurements with charts, and catches every personal record automatically as your lean mass grows.
What Is Lean Body Mass?
Lean body mass (LBM) is your body weight minus fat mass: your muscle, bone, organs, water and everything else that isn't fat. It's a useful number for setting protein intake, dosing by body weight, or tracking muscle gain separately from fat loss.
How This Lean Body Mass Calculator Works
Enter your height and weight, and this calculator runs three published formulas at once, each estimating lean mass from your weight (W, in kg) and height (H, in cm) alone.
Lean body mass formulas, men and women
| Formula | Men | Women |
|---|---|---|
| Boer | 0.407W + 0.267H - 19.2 | 0.252W + 0.473H - 48.3 |
| James | 1.1W - 128(W/H)² | 1.07W - 148(W/H)² |
| Hume | 0.32810W + 0.33929H - 29.5336 | 0.29569W + 0.41813H - 43.2933 |
For a man 80 kg and 180 cm tall, the formulas give 61.4 kg (Boer), 62.7 kg (James) and 57.8 kg (Hume), a spread of about 5 kg between the highest and lowest estimate.
The James formula becomes unreliable at very high body weights, so treat its result with more caution if you're a heavier lifter.
Lean Body Mass From Body Fat Percentage
If you know your body fat percentage, from calipers, a scan or the body fat calculator, lean mass = weight x (1 - body fat % / 100). It's the most personal of the four estimates here, since it's based on your own measured leanness rather than a population formula.
Which Lean Body Mass Formula Is Best?
No single formula fits everyone; each comes from a different study population. The Boer formula (1984) and Hume formula (1966) are both widely used, while the James formula (1976) can drift at very high body weights.
If you know your body fat percentage, that estimate is generally the most personal, since it isn't based on a population average.
Lean Body Mass and FFMI
Lean body mass feeds directly into FFMI (fat-free mass index), which divides lean mass by height squared to compare muscularity across different heights. See the FFMI calculator to check where your lean mass puts you against population percentiles.
Used by lifters following PPL, 5x5, upper/lower, and more.
Frequently Asked Questions
What is lean body mass?
Lean body mass (LBM) is your body weight minus fat mass: everything else, muscle, bone, organs and water. It's commonly used to set protein targets or track muscle gain separately from fat loss.
How do I calculate lean body mass?
Enter your height and weight above to get three formula-based estimates (Boer, James and Hume), or enter your body fat percentage for a fourth, more personal estimate: weight x (1 - body fat % / 100).
What is the most accurate lean body mass formula?
None of the three fits everyone equally, since each comes from a different study population. If you know your body fat percentage, that estimate is generally the most personal, since it's based on your own measured leanness.
Is the James formula accurate?
It's a widely used formula from 1976, but it becomes unreliable at very high body weights. The Boer and Hume formulas are also widely used, and this calculator shows all three so you can compare them for your own numbers.
What's the difference between lean body mass and FFMI?
Lean body mass is a weight, in kilograms or pounds. FFMI (fat-free mass index) divides that lean mass by your height squared, so lifters of different heights can be compared on the same scale. See the FFMI calculator.
How much lean body mass should I have?
It depends on your height, sex and training history, since lean mass scales with body size. Comparing your FFMI, which adjusts for height, is a more useful benchmark than a raw lean mass number.
Sources
More Free Tools
FFMI Calculator
Calculate your FFMI and normalized FFMI, and see how your muscle mass compares to population percentiles by sex.
Body Fat Calculator
Estimate your body fat percentage with the U.S. Navy tape method or BMI, and see your ACE body fat category.
Army Body Fat Calculator
Check the Army's waist-to-height ratio standard (0.55) or the 2023 one-site tape test it replaced.
1RM Calculator
Estimate your one-rep max from any set, with a rep-max chart and NSCA training percentages.
Strength Calculator
See your squat, bench and deadlift percentile against real competitive lifters in your weight class.
RPE Calculator
Convert RPE to a percentage of your 1RM, or find the load for a target reps and RPE.
