Lean Body Mass Calculator

Calculate your lean body mass using multiple scientific formulas including Boer, James, and Hume.

100% Free No Sign-Up Calculated in Your Browser

Sex

Weight (kg)

Height (cm)

Feet

Inches

Body Fat % (optional)

If provided, a direct body-fat based calculation is also shown.

Average Lean Body Mass

– kg

Enter your details and press Calculate

Body Fat Mass

–

LBM by Boer

–

Most widely used

LBM by James

–

Clinical reference

LBM by Hume

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Regression model

LBM via Body Fat % (direct)

–

Weight × (1 − BF% / 100)

Formula reference:
Boer: Male: 0.407W + 0.267H − 19.2 | Female: 0.252W + 0.473H − 48.3
James: Male: 1.1W − 128(W/H)² | Female: 1.07W − 148(W/H)²
Hume: Male: 0.3281W + 0.3393H − 29.5336 | Female: 0.2296W + 0.4215H − 21.4956
(W = kg, H = cm)

Estimate your lean body mass — everything in your body besides fat — using three peer-reviewed formulas (Boer, James, and Hume), or directly from a known body fat percentage.

How It Works

How Lean Body Mass Calculator Works

The Boer formula, widely used in clinical settings, is: 0.407 × weight(kg) + 0.267 × height(cm) − 19.2 for men, and 0.252 × weight + 0.473 × height − 48.3 for women. It was derived from body density measurements and is considered a solid general-purpose estimate.

The James formula instead uses a weight-to-height-squared ratio: 1.1 × weight − 128 × (weight ÷ height)² for men, with different coefficients for women. The Hume formula is a separate regression equation — 0.3281 × weight + 0.3393 × height − 29.5336 for men — derived independently from its own reference dataset. Averaging the three reduces the influence of any single formula's blind spots.

If you separately know your body fat percentage (say, from a body fat calculator or a DEXA scan), the tool also shows a direct calculation: LBM = weight × (1 − body fat % ÷ 100), which sidesteps the height/weight-only formulas entirely and can be more accurate for your specific body composition.

Worked Example

See It In Action

For a man weighing 80 kg at 178 cm: Boer gives about 60.9 kg, James gives about 62.1 kg, and Hume gives about 57.1 kg — averaging to roughly 60.0 kg (132.4 lbs) of lean body mass. That implies a fat mass of about 20.0 kg (44.0 lbs), or an estimated body fat of around 24.9%.

Real-World Use Cases

Who Uses Lean Body Mass Calculator and Why

Getting a blended lean mass estimate from three independent formulas rather than trusting just one.
Calculating lean mass directly from a known body fat percentage, bypassing the height/weight-only formulas.
Setting protein targets based on lean mass rather than total weight, particularly for someone carrying more fat than average.

Common Mistakes

Mistakes to Avoid

Entering an inaccurate body fat percentage into the direct-calculation field, since that shortcut is only as good as the number you feed it — a rough visual guess can throw off the result more than using the three formulas alone.
Expecting the three height/weight formulas to be highly accurate for an atypical build — they're population-level estimates and tend to underestimate lean mass for very muscular individuals.
Confusing lean body mass with muscle mass specifically — LBM includes bone, organs, and water in addition to muscle, so it's always higher than muscle mass alone.

Pro Tips

Tips for Best Results

If you have a reasonably reliable body fat percentage from a body fat calculator or a scan, the direct calculation is usually more personalized than averaging the three general formulas.
Use the averaged three-formula estimate as your default when you don't have a body fat percentage on hand — averaging reduces the impact of any one formula's blind spots.

Troubleshooting

Fixing Common Problems

The three formulas gave noticeably different results. — This is expected since each was derived from an independent research population — a spread of a few kilograms between them is normal; the average is generally a more stable estimate than any single formula.

Glossary

Terms Explained

Lean body mass (LBM): Total body weight minus fat mass — includes muscle, bone, organs, and water.

FAQ

Frequently Asked Questions

Why average three different formulas?

Each formula was derived from a different research population and carries its own systematic bias — averaging reduces the impact of any single formula's specific quirks and tends to produce a more stable estimate than relying on just one.

How is this different from a body fat percentage calculator?

A body fat calculator estimates your fat percentage directly (often from circumference measurements), while this tool estimates lean mass from height and weight alone — though if you already know your body fat percentage, the direct calculation shown here uses that instead.

Why does lean body mass matter for fitness or nutrition?

Lean mass is often used to set more precise protein targets (grams per kg of lean mass rather than total weight) and is a better indicator of muscle-building progress than total body weight alone, since it excludes fat fluctuations.

Are these formulas accurate for everyone?

They are population-level estimates and can be less precise for people with atypical body composition — very muscular athletes, for example, may have their lean mass underestimated by formulas calibrated on a general population.