Lean Body Mass Calculator - Boer, James, Hume Formulas

Lean body mass from height and weight, by four published equations

A man who weighs 180 lb at 5 ft 10 in gets four different answers for his lean body mass: 135.6 lb from Boer, 138.5 lb from James, 126.9 lb from Hume and 136.1 lb from Janmahasatian. None of them is wrong in the arithmetic. They were fitted to different groups of people, and that spread of 11.6 lb is the honest size of the uncertainty when all you know is height and weight. This calculator runs all four side by side in pounds or kilograms, shows the range, drops the James equation where its curve turns down, and, if you have a body fat percentage from a scan or a caliper test, puts your measured lean mass next to the estimates.

What goes into the form

Sex - every equation has one set of coefficients for men and another for women.
Units - U.S. (pounds, feet and inches) or metric (kilograms, centimeters). The equations themselves work in kg and cm; the conversion is done for you.
Weight - from 66 to 661 lb (30 to 300 kg). Decimals are fine.
Height - whole feet plus inches, or centimeters, from 120 to 230 cm.
Body fat % (optional) - only if you have a measured figure, from 3 to 70. Leave it empty otherwise; the calculator does not guess it.
Read the result - the range of the equations that apply to you, each equation on its own row, and your measured lean mass when you gave a body fat percentage.

The four equations compared

Coefficients as tabulated by Puri and colleagues in the British Journal of Radiology, with W in kilograms and H in centimeters. The right-hand column is their 95% limits of agreement against DXA scans of 1,558 adults aged 60-65, men and women pooled.

Equation	Men	Women	Agreement
Boer	0.407W + 0.267H - 19.2	0.252W + 0.473H - 48.3	13.1 kg
James	1.10W - 128(W/H)²	1.07W - 148(W/H)²	14.2 kg
Hume	0.32810W + 0.33929H - 29.5336	0.29569W + 0.41813H - 43.2933	16.9 kg
Janmahasatian	9270W / (6680 + 216 BMI)	9270W / (8780 + 244 BMI)	12.3 kg

The James row in that paper is the version used by Hallynck and colleagues. Janmahasatian estimates fat-free mass, which these formulas treat as the same quantity. In the same comparison Janmahasatian was the best fit for women, and for men it was within the margin of the best one, an equation by Gallagher that needs age and is not included here.

Three people, by hand and by the calculator

Man, 80 kg, 180 cm. Boer: 0.407 × 80 + 0.267 × 180 - 19.2 = 32.56 + 48.06 - 19.2 = 61.4 kg. James: 1.10 × 80 - 128 × (80 / 180)² = 88 - 25.28 = 62.7 kg. Hume: 26.25 + 61.07 - 29.53 = 57.8 kg. The calculator shows 57.8 to 62.7 kg, about 75% of body weight at the middle.

Woman, 140 lb, 5 ft 5 in (63.5 kg, 165.1 cm). Boer 101.0 lb, James 101.5 lb, Hume 98.1 lb, Janmahasatian 89.7 lb. Here Janmahasatian sits 8.4 to 11.8 lb below the other three, so the range runs 89.7 to 101.5 lb.

Man, 220 lb, 6 ft 0 in, body fat measured at 25%. Lean mass from the measurement: 220 × 0.75 = 165.0 lb. The equations put him at 143.9 to 158.0 lb, so his measured figure sits above all four of them.

Lean body mass ranges at a typical height

The calculator's range for a man of 5 ft 10 in and a woman of 5 ft 5 in at four weights each. Each extra 30 lb moves the middle of the range up by only 6.9 to 12.3 lb, so the equations count most of the added weight as fat.

Person	Weight	BMI	Lean mass range
Man, 5 ft 10 in	150 lb	21.5	117.1 to 123.7 lb
Man, 5 ft 10 in	180 lb	25.8	126.9 to 138.5 lb
Man, 5 ft 10 in	210 lb	30.1	136.8 to 150.0 lb
Man, 5 ft 10 in	240 lb	34.4	146.6 to 160.0 lb
Woman, 5 ft 5 in	120 lb	20.0	81.5 to 95.9 lb
Woman, 5 ft 5 in	140 lb	23.3	89.7 to 101.5 lb
Woman, 5 ft 5 in	170 lb	28.3	100.5 to 110.7 lb
Woman, 5 ft 5 in	200 lb	33.3	109.7 to 116.1 lb

Why the James equation is switched off at high BMI

James subtracts a term that grows with the square of weight. Past a certain point the subtraction wins and the equation starts giving less lean mass for more weight. Setting its slope to zero gives the turning point: a BMI of 43.0 for men and 36.1 for women. Puri and colleagues, citing Nyman, describe the same plateau at about 43 and 37. A woman at 5 ft 4 in shows it clearly: at 200 lb James gives 112.4 lb of lean mass, at 230 lb only 111.7 lb. Beyond the turning point the calculator still prints the James figure with a star, but leaves it out of the range.

Mistakes that skew a lean mass estimate

Reading lean mass as muscle. Lean body mass is everything that is not fat, so it includes bone, organs and body water as well as muscle. A gain in lean mass on a scan is not automatically a gain in muscle.

Expecting the equations to see training. They know only height and weight, so two people of the same size get the same estimate however much muscle they carry. A lean man of 160 lb at 5 ft 8 in with 12% body fat has 140.8 lb of lean mass by measurement, while the equations say 116.6 to 126.2 lb.

Taking one equation as the answer. With limits of agreement of 12 to 17 kg in the comparison above, the difference between two equations is usually smaller than the error of either one. The range is the more truthful output.

Using it for a dose. These equations are used in medicine, for example to scale contrast or tracer doses, but that is a clinician's calculation with its own protocol. Do not adjust any medication from this page.

Short answers on lean body mass

Which lean body mass formula is most accurate?

It depends on the measure. Against DXA in adults aged 60-65, Hume had the smallest average bias of the four (-1.1 kg, men and women pooled) but the widest limits of agreement (16.9 kg); Janmahasatian had the narrowest limits (12.3 kg) and was the best fit for women. No single equation wins on every count, which is why the calculator shows all of them.

How do I calculate lean body mass from body fat percentage?

Multiply weight by (1 - body fat / 100). At 200 lb and 20% body fat that is 200 × 0.80 = 160 lb. The result is only as good as the body fat measurement.

Why does an equation say "not valid"?

For extreme combinations, for example a very light and very tall person, a linear equation can return more lean mass than the whole body weight. The calculator flags that row and builds the range from the others.

Is lean body mass the same as fat-free mass?

The equations here treat them as the same thing, and Janmahasatian is published as a fat-free mass equation. If a lab report gives both, use the figure it labels as fat-free mass for comparison.

Related tools

Body Surface Area Calculator

BSA in m2 and square feet by five formulas, from Mosteller to Boyd - See the calculator

Adult Height Percentile Calculator

Your height as a percentile of U.S. men or women of your age group - See the calculator

Body Fat Percentage Calculator

Body fat from tape measurements by the U.S. Navy method, the figure this page can take as input - See the calculator

FFMI Calculator

Fat-free mass set against height, with the published reference markers - See the calculator

BMR & TDEE Calculator

Resting and daily energy needs from your size, age and activity - See the calculator

Protein Intake Calculator

Daily protein in grams for your weight and goal - See the calculator

Ideal Weight Calculator

Weight ranges for your height from the classic formulas - See the calculator