Lean Body Mass Calculator
Boer lean body mass from height, weight, and sex, with fat mass shown.
What it does
A scale reports one number for everything you carry. Lean body mass splits that number in two: the fat free part (muscle, bone, organs, skin, and water) and the stored fat part. Clinicians use the split to dose drugs that stay out of fat tissue, and lifters use it to check whether scale gains are muscle or padding.
The tool above runs the Boer equation from 1984, fitted on measured body fluid volumes in 66 healthy adults. Men use 0.407 per kilogram plus 0.267 per centimeter minus 19.2; women use 0.252 per kilogram plus 0.473 per centimeter minus 48.3. Pick metric or imperial and the math converts behind the scenes.
The worked default is a man at 80 kg and 180 cm. His estimate is 61.4 kg lean, leaving 18.6 kg of fat, or 23.2 %. The imperial mirror (176.4 lb, 70.9 in) returns the same split at 135.5 lb lean. Both modes were run through the page tool before publishing.
No height weight formula sees individuals clearly. Very muscular, very lean, or obese builds all sit away from the study population, so errors of a few kilograms are normal. For a precise reading, pair the estimate with a body fat measurement or a DEXA scan, and watch the trend across months instead of judging one number.
This page is schooling material, not medical advice. Drug dosing, kidney estimates, and nutrition plans built on lean mass belong under a clinician or pharmacist, who will pick the right formula for the patient in front of them.
How to use
- Pick metric or imperial units.
- Select male or female for the matching equation.
- Type current weight without clothes or after the same meal each time.
- Type standing height in cm or inches.
- Read lean mass first, then fat mass and the implied percent.
- Repeat monthly under the same conditions and compare the lean line.
Formula
- LBM
- Lean body mass in kg.
- W
- Body weight in kg.
- H
- Standing height in cm.
- 19.2 / 48.3
- Regression constants for men and women.
Boer fitted each sex separately, so the coefficients genuinely differ instead of sharing one line with an offset. The male form leans on weight (0.407) while the female form leans on height (0.473). Hume 1966 and James 1976 offer sibling equations, but this page standardizes on Boer as the headline.
Worked example
Example: man, 80 kg, 180 cm
Metric defaults already filled in the form.
- Weight term: 0.407 x 80 = 32.56.
- Height term: 0.267 x 180 = 48.06.
- Sum minus constant: 32.56 + 48.06 - 19.2 = 61.42, shown as 61.4 kg.
- Fat mass: 80 - 61.42 = 18.58, shown as 18.6 kg.
- Implied fat: 18.58 / 80 x 100 = 23.2 %.
- Imperial check: 176.4 lb and 70.9 in convert to the same inputs and return 135.5 lb lean at 23.2 %.
Reference table
| Weight | Lean mass | Implied fat |
|---|---|---|
| 70 kg | 57.4 kg | 18.1 % |
| 80 kg | 61.4 kg | 23.2 % |
| 90 kg | 65.5 kg | 27.2 % |
| 100 kg | 69.6 kg | 30.4 % |
Limits
- Population regression, not a measurement: expect a few kilograms of error per person.
- Accuracy falls at the extremes: heavily muscled, very lean, obese, pregnant, or fluid overloaded readers.
- The implied fat percent assumes all non lean mass is fat, which misreads bone dense athletes.
- Not validated for children; adult equations only.
Common mistakes
- Reading lean mass as muscle mass. Muscle is only the largest slice of the lean total.
- Mixing units, like pounds with the kg coefficients. Use the unit toggle instead.
- Weighing at random times of day and blaming the formula for water swings.
- Comparing two people instead of tracking one person over time.
- Using the result to dose medicine without a clinician.
Try it yourself
Quick checks. Answers sit tucked under each question.
Woman, 60 kg, 165 cm. Lean mass?
0.252 x 60 + 0.473 x 165 - 48.3 = 44.9 kg, with 15.1 kg fat (25.2 %).
Man, 90 kg, 180 cm. Implied fat percent?
LBM = 65.5 kg, fat = 24.5 kg, share = 27.2 %.
Which input moves the male result more, 1 kg or 1 cm?
1 kg adds 0.407 kg lean; 1 cm adds 0.267 kg. Weight moves it more.
Questions
What is lean body mass?
Everything except stored fat: muscle, bone, organs, skin, and body water.
Why do men and women use different formulas?
Boer fitted the sexes separately and the weight height balance genuinely differs.
Is lean mass the same as muscle?
No. Muscle is the biggest part of lean mass, but bone and organs count too.
How accurate is the Boer estimate?
A few kilograms either way for typical adults; worse for extreme builds.
What is a normal lean mass?
Roughly 75 to 85 % of weight for men and 65 to 75 % for women, varying with frame.
Can I use this to dose drugs?
Only with a clinician. Dosing picks formulas per drug and patient.
Sources
- Boer P, Am J Physiol 1984 (PubMed 6496691)
- Boer P, estimated lean body mass paper (Physiology journal)