How to Calculate Lean Body Mass: The Formulas, Worked Examples, and What to Do With Your Number

If you want to learn how to calculate lean body mass, you only need three inputs: your weight, your height, and your sex. Lean body mass, usually shortened to LBM, is everything in your body that is not stored fat. That includes muscle, bone, organs, water, and a small amount of essential fat. It is the number trainers use to set protein targets, the number some doctors use for drug dosing, and a far better progress tracker than scale weight alone.

This guide shows you how to calculate lean body mass three ways: the Boer, James, and Hume formulas, each with full worked examples for a man and a woman. You will also learn how to calculate lean body mass from a body fat percentage, what a good number looks like, and how to turn your result into a daily protein target.

Quick Answer: How to Calculate Lean Body Mass?

Here is how to calculate lean body mass in one step. Use the Boer formula, the most widely used option for adults. For men: LBM = 0.407 x weight in kg + 0.267 x height in cm – 19.2. For women: LBM = 0.252 x weight in kg + 0.473 x height in cm – 48.3. The answer comes out in kilograms. That one-sentence version is the fastest way to learn how to calculate lean body mass, and the sections below show the other two formulas for comparison.

A man who weighs 80 kg and stands 180 cm tall has a lean body mass of about 61.4 kg by the Boer formula. A woman who weighs 62 kg and stands 165 cm tall has about 45.4 kg. If you want to skip the arithmetic, our lean body mass calculator does the same math instantly and shows all three formulas side by side.

What Is Lean Body Mass?

Lean body mass is your total body weight minus your stored fat. If you weigh 80 kg and carry 16 kg of stored fat, your lean body mass is 64 kg. That 64 kg is not just muscle. It includes your bones, your organs, your skin, your blood, and all the water in your body. It also includes a small amount of essential fat, the fat your body needs to protect your organs and keep your cells working.

Two people can weigh exactly the same and have very different lean body mass. A trained lifter and a sedentary person who both weigh 80 kg might differ by 10 kg of lean mass or more. That is why scale weight alone is such a weak measure of progress. Learning how to calculate lean body mass is what turns a confusing scale reading into a useful body composition number.

Lean body mass also matters because it drives your metabolism. Muscle and organs burn far more energy at rest than fat tissue does. So a person with more lean mass burns more calories doing nothing. That is why lean body mass shows up in calorie and protein calculations, and why protecting it during fat loss matters so much.

Lean Body Mass vs Fat-Free Mass vs Skeletal Muscle Mass

These three terms get mixed up constantly, even by fitness writers. They are related, but they are not the same thing. Here is the difference in plain language.

Term	What it includes	What it leaves out
Lean body mass (LBM)	Muscle, bone, organs, water, connective tissue, plus essential fat	Stored fat only
Fat-free mass (FFM)	Muscle, bone, organs, water, connective tissue	All fat, including essential fat
Skeletal muscle mass	Skeletal muscle only	Bone, organs, water, all fat

The gap between lean body mass and fat-free mass is small. Lean body mass includes essential fat, roughly 2 to 3 percent of body weight in men and 5 to 12 percent in women. Fat-free mass excludes it. In practice, most fitness and nutrition advice uses the two terms interchangeably, and the difference rarely changes what you should do. The distinction matters more when you learn how to calculate lean body mass, because DEXA reports and formula results use slightly different definitions.

The gap between lean body mass and skeletal muscle mass is much bigger. Skeletal muscle is typically only 35 to 50 percent of your lean body mass. So if your lean body mass is 60 kg, your actual skeletal muscle might be 21 to 30 kg. This is the most common misunderstanding about lean body mass. Gaining 2 kg of lean mass does not mean you gained 2 kg of new muscle. It could be water, glycogen, or measurement noise.

One more wrinkle: a DEXA scan reports “lean mass” as lean soft tissue, which excludes bone mineral content. Formula-based lean body mass includes bone and essential fat, so your formula result will usually read about 6 to 10 percent higher than a DEXA lean mass figure. Neither is wrong. They are measuring slightly different things.

Does Lean Body Mass Include Bone?

Yes, formula-based lean body mass includes bone mineral content, along with muscle, organs, water, and essential fat. This is one reason a formula result reads higher than a DEXA scan’s “lean mass” figure, because DEXA reports lean soft tissue separately from bone. Expect your formula estimate to run about 6 to 10 percent higher than a DEXA lean mass reading. The two are measuring slightly different things, and neither is wrong. If you are comparing a DEXA report with a guide to how to calculate lean body mass, expect that gap and do not chase it.

The 3 Formulas at a Glance

Three published formulas show how to calculate lean body mass from height, weight, and sex. All three were developed from clinical research, and all three take the same inputs. They disagree by a few kilograms on the same person, which tells you something honest: a formula gives an estimate, not a measurement.

Formula	Year	Men	Women	Originally built for
Boer	1984	0.407 x W + 0.267 x H – 19.2	0.252 x W + 0.473 x H – 48.3	Drug dosing, body fluid volumes
James	1976	1.10 x W – 128 x (W / H) squared	1.07 x W – 148 x (W / H) squared	Obesity research, body size
Hume	1966	0.32810 x W + 0.33929 x H – 29.5336	0.29569 x W + 0.41813 x H – 43.2933	Creatinine clearance, kidney patients

In every formula, W is weight in kilograms and H is height in centimeters. If you measure in pounds and inches, convert first: divide pounds by 2.205 to get kilograms, and multiply inches by 2.54 to get centimeters. BodySpec has a clear reference for all four LBM formulas, including the pediatric Peters formula, in its ultimate lean body mass calculator guide.

Which formula should you use? For most healthy adults, Boer is the best default. It is the most widely used in clinical work, and it behaves well across typical body sizes. James uses a squared weight-to-height ratio, which makes it behave differently at the extremes, very lean or very heavy. Hume is the oldest of the three, fitted on a small sample of kidney patients, and it tends to read a little low. The sections below work all three formulas for the same two people, so you can see the spread for yourself. Each of the three answers how to calculate lean body mass slightly differently, which is why comparing them is more honest than trusting one alone.

How to Calculate Lean Body Mass With the Boer Formula

The Boer formula is the one to use if you only use one. It is a simple linear equation, and it is the formula most calculators show first. Here it is again, with units spelled out.

For men: LBM = 0.407 x weight in kg + 0.267 x height in cm – 19.2

For women: LBM = 0.252 x weight in kg + 0.473 x height in cm – 48.3

Worked example, man: 80 kg, 180 cm tall (about 176 lb and 5 ft 11 in).

Step 1: 0.407 x 80 = 32.56

Step 2: 0.267 x 180 = 48.06

Step 3: 32.56 + 48.06 – 19.2 = 61.42 kg

So this man has about 61.4 kg of lean body mass, or about 135 lb. His stored fat is 80 – 61.4 = 18.6 kg, which means his implied body fat is about 23 percent.

Worked example, woman: 62 kg, 165 cm tall (about 137 lb and 5 ft 5 in).

Step 1: 0.252 x 62 = 15.624

Step 2: 0.473 x 165 = 78.045

Step 3: 15.624 + 78.045 – 48.3 = 45.369 kg

So this woman has about 45.4 kg of lean body mass, or about 100 lb. Her stored fat is 62 – 45.4 = 16.6 kg, which means her implied body fat is about 27 percent. Once you have run the Boer formula once, you know how to calculate lean body mass for anyone with a scale and a tape measure.

How to Calculate Lean Body Mass With the James Formula

The James formula takes a different shape, and it is the second classic answer to how to calculate lean body mass. Instead of two separate terms for weight and height, it uses a squared weight-to-height ratio. That makes it more sensitive to body proportions, but also less predictable at the extremes.

For men: LBM = 1.10 x W – 128 x (W / H) squared, with W in kg and H in cm.

For women: LBM = 1.07 x W – 148 x (W / H) squared, with W in kg and H in cm.

Worked example, same man: 80 kg, 180 cm.

Step 1: 1.10 x 80 = 88

Step 2: 80 / 180 = 0.4444, squared = 0.1975

Step 3: 128 x 0.1975 = 25.28

Step 4: 88 – 25.28 = 62.72 kg

Worked example, same woman: 62 kg, 165 cm.

Step 1: 1.07 x 62 = 66.34

Step 2: 62 / 165 = 0.3758, squared = 0.1412

Step 3: 148 x 0.1412 = 20.90

Step 4: 66.34 – 20.90 = 45.44 kg

Notice that James reads slightly higher than Boer for both people: 62.7 vs 61.4 kg for the man, 45.4 vs 45.4 kg for the woman (effectively tied). James tends to read high for average male builds, which is one reason Boer is usually preferred. The James formula shows how to calculate lean body mass with a different shape of equation, and the comparison below shows why that shape matters.

How to Calculate Lean Body Mass With the Hume Formula

The Hume formula is the oldest of the three answers to how to calculate lean body mass, published in 1966. Like Boer, it is a linear equation with separate weight and height terms, but with different coefficients. It was fitted on a small group of adults, many with kidney disease, so treat it as a second opinion rather than the headline.

For men: LBM = 0.32810 x W + 0.33929 x H – 29.5336, with W in kg and H in cm.

For women: LBM = 0.29569 x W + 0.41813 x H – 43.2933, with W in kg and H in cm.

Worked example, same man: 80 kg, 180 cm.

Step 1: 0.32810 x 80 = 26.248

Step 2: 0.33929 x 180 = 61.072

Step 3: 26.248 + 61.072 – 29.5336 = 57.786 kg

Worked example, same woman: 62 kg, 165 cm.

Step 1: 0.29569 x 62 = 18.333

Step 2: 0.41813 x 165 = 68.991

Step 3: 18.333 + 68.991 – 43.293 = 44.031 kg

Hume reads lower than the other two for both people, which matches its reputation. It still lands within a few kilograms, and that spread is the honest uncertainty of formula-based estimation. The Hume formula rounds out the three classic answers to how to calculate lean body mass, and it usually reads a little low.

All 3 Formulas Side by Side

Here is what the three formulas give for the same two people. This is the comparison most calculators skip, and it is the reason you should never treat a single formula result as exact.

Person	Boer (1984)	James (1976)	Hume (1966)	Spread
Man, 80 kg, 180 cm	61.4 kg	62.7 kg	57.8 kg	4.9 kg
Woman, 62 kg, 165 cm	45.4 kg	45.4 kg	44.0 kg	1.4 kg

The man shows a spread of almost 5 kg between the highest and lowest formula. The woman shows a tighter spread of 1.4 kg. The practical takeaway: use Boer as your headline number, note the range, and judge progress by the trend over time, not by a single reading. If your Boer estimate rises by 2 kg over six months while your weight stays flat, that is a real signal, even if the absolute number carries a few kilograms of uncertainty. That is the real lesson when you learn how to calculate lean body mass: the trend beats any single number.

A fourth formula, Peters (2011), exists but is only for children aged 13 to 14 years or younger. It estimates lean body mass from an extracellular volume equation. Adults should not use it. If you are calculating lean body mass for a child, a pediatrician should be involved, because children’s body composition changes fast with growth.

How to Calculate Lean Body Mass From Body Fat Percentage

If you already know your body fat percentage from a reliable measurement, you do not need any of the three formulas. The direct method is simple arithmetic, and it is more accurate than a formula estimate, because it uses your actual body composition instead of a population average.

LBM = total body weight x (1 – body fat percentage as a decimal)

Worked example, man: 80 kg at 20 percent body fat.

LBM = 80 x (1 – 0.20) = 80 x 0.80 = 64 kg

Compare that with his Boer estimate of 61.4 kg. The direct method says 64 kg because this man is leaner than the average person his height and weight. The formula could not know that. It assumed an average body composition, and he beat the average.

Worked example, woman: 62 kg at 28 percent body fat.

LBM = 62 x (1 – 0.28) = 62 x 0.72 = 44.64 kg, or about 44.6 kg

That is close to her Boer estimate of 45.4 kg, because her body composition is near average for her size. The direct method only beats the formulas when the body fat figure is trustworthy. This direct method is the most accurate way to learn how to calculate lean body mass, as long as the body fat figure behind it is trustworthy. A DEXA scan or a careful skinfold test qualifies. A smart scale estimate or a visual guess does not, because its error goes straight into your lean body mass number. If you need a body fat figure first, our guide to how to calculate body fat percentage covers the methods from cheapest to most accurate.

Lean Body Mass Chart by Height

The table below shows Boer lean body mass at each height, for a person at a BMI of 22, right in the middle of the healthy range. Use it as a rough benchmark. Your own number will sit above this line if you carry more muscle than average, and below it if you carry more fat.

Height	Weight at BMI 22	Boer LBM, men	Boer LBM, women
5 ft 0 in (152 cm)	51.1 kg	42.3 kg	36.7 kg
5 ft 2 in (157 cm)	54.6 kg	45.1 kg	40.0 kg
5 ft 4 in (163 cm)	58.2 kg	47.9 kg	43.3 kg
5 ft 6 in (168 cm)	61.8 kg	50.7 kg	46.6 kg
5 ft 8 in (173 cm)	65.6 kg	53.6 kg	49.9 kg
5 ft 10 in (178 cm)	69.6 kg	56.6 kg	53.3 kg
6 ft 0 in (183 cm)	73.6 kg	59.6 kg	56.8 kg
6 ft 2 in (188 cm)	77.8 kg	62.7 kg	60.2 kg

A quick sanity check for any adult: lean body mass is typically 75 to 90 percent of total body weight in men, and 68 to 85 percent in women. If your formula result falls far outside those bands, double check your unit conversions, especially centimeters vs meters in the height term. That single mistake is the most common reason for a wildly wrong answer. Use the chart as a starting point, then learn how to calculate lean body mass with your own measurements to get your personal number. If you want the healthy weight range for your height, our guide to how to calculate BMI shows how the BMI bands translate into kilograms and pounds.

What to Do With Your Lean Body Mass Number

A lean body mass number is only useful if it changes a decision. Once you know how to calculate lean body mass, here are the three decisions it should drive.

Set your protein target from lean mass, not total weight

Fat tissue needs almost no protein to maintain itself, so basing protein on total body weight overfeeds people with more body fat and underfeeds very lean people. The evidence-based range for people who lift weights is 1.6 to 2.2 grams of protein per kilogram of lean body mass per day, which works out to roughly 0.7 to 1.0 grams per pound of lean mass.

Worked example, the man above (61.4 kg LBM): 1.6 x 61.4 = 98 grams at the low end, 2.2 x 61.4 = 135 grams at the high end. So about 98 to 135 grams of protein per day.

Worked example, the woman above (45.4 kg LBM): 1.6 x 45.4 = 73 grams at the low end, 2.2 x 45.4 = 100 grams at the high end. So about 73 to 100 grams per day.

If you are dieting, aim toward the high end, because a calorie deficit raises protein needs for muscle preservation. If you are older, also aim higher, because aging blunts the muscle-building response to protein. For the full picture of splitting those calories across protein, carbs, and fat, see our guide to how to calculate macros. That guide starts from the same place: once you know how to calculate lean body mass, protein becomes a simple multiplication.

Estimate your BMR from lean mass

The Katch-McArdle equation estimates basal metabolic rate directly from lean body mass: BMR = 370 + 21.6 x LBM in kg. It is more accurate than weight-based formulas for muscular or very lean people, because it uses what actually burns calories.

Man above: 370 + 21.6 x 61.4 = 370 + 1,326 = 1,696 kcal per day at rest.

Woman above: 370 + 21.6 x 45.4 = 370 + 981 = 1,351 kcal per day at rest.

Multiply that resting number by your activity level to get your daily calorie target. Our guide to how to calculate BMR walks through the activity multipliers, and our guide to how many calories a day turns the result into a full daily plan. Both guides build on the same skill: knowing how to calculate lean body mass lets you estimate calorie needs from what actually burns calories.

Track the trend, and check FFMI for context

Recalculate your lean body mass every 4 to 6 weeks, under the same conditions. The trend is the signal. If your weight is flat but your lean body mass is rising, you are gaining muscle and losing fat at the same time, which is the best outcome a scale can hide. If your weight is falling but your lean body mass is falling fast too, your deficit is too steep or your protein is too low, and you are losing muscle along with fat.

One more useful number is the fat-free mass index, FFMI = LBM / height in meters squared. The man above scores 61.4 / (1.80 x 1.80) = 19.0. The woman scores 45.4 / (1.65 x 1.65) = 16.7. FFMI lets you compare lean mass across heights. A height-normalized version, which adds 6.1 x (1.8 – height in meters), adjusts further for tall and short frames. If the scale has been stuck for weeks despite a deficit, our guide to why am i not losing weight covers the other reasons a stall happens, including muscle gain masking fat loss. That is the payoff for learning how to calculate lean body mass: the scale stops lying to you.

How Much Protein Should I Eat per Kg of Lean Body Mass?

People who lift weights should aim for 1.6 to 2.2 grams of protein per kilogram of lean body mass per day, or about 0.7 to 1.0 grams per pound of lean mass. A person with 61 kg of lean mass needs roughly 98 to 135 grams per day. Aim toward the high end while dieting or as you get older. People who do not train hard can use 1.2 to 1.6 grams per kilogram of lean mass. The general RDA of 0.8 grams per kilogram of total body weight is a minimum to prevent deficiency, not a target for building or preserving muscle. Start by learning how to calculate lean body mass, then multiply by the range above.

How Often Should I Recalculate Lean Body Mass?

Every 4 to 6 weeks is enough. Body composition changes slowly, and weekly readings mostly show water and food noise. Weigh yourself under the same conditions each time, first thing in the morning after the bathroom, and use the same formula. Track the trend over at least three readings before changing your plan. If your lean body mass is falling while you diet, raise protein, slow the deficit, or add resistance training before the loss becomes a pattern. That routine, learning how to calculate lean body mass every month or so, turns body composition from a mystery into a tracked metric.

Limitations: What the Formulas Cannot Tell You

Formula estimates have real limits, and an honest article should name them. The limits below apply to every method of how to calculate lean body mass from height and weight.

First, the formulas assume average body composition. They cannot tell a 80 kg lifter from a 80 kg sedentary person of the same height and sex. Both get the same Boer number. Only a measured body fat percentage or a DEXA scan separates them.

Second, James behaves oddly at the extremes. Its squared ratio term can produce unrealistic results for very heavy or very short people, and in some cases it can even return a number above total body weight. If a formula result exceeds your total weight, the formula has failed for your body size, not the other way around.

Third, hydration swings the numbers. Your weight changes by 1 to 2 kg through a normal day as you eat, drink, and sweat. That flows straight into the formula result. Weigh yourself first thing in the morning, after the bathroom, for consistent readings.

Fourth, these formulas are for adults. Children, pregnant women, and people with conditions that change fluid balance, like kidney disease or heart failure, should not rely on them. The Peters formula exists for children, but it belongs in a clinical setting.

Finally, remember that a formula is an estimate, not a measurement. DEXA remains the reference standard for body composition, with hydrostatic weighing and BodPod close behind. Use formulas for tracking and planning, and a scan when the number really matters, like before a medical procedure or a serious training block.

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