Lean Body Mass (LBM) Calculator
Boer LBM, U.S. Navy body fat (optional), and Du Bois BSA—instant results with metric or imperial.
Your measurements
Results
- LBM uses the Boer equation (adult general population).
- Body fat uses the U.S. Navy tape method (optional; needs neck/waist and hip for women).
- BSA uses the Du Bois & Du Bois formula.
Results interpretation
- LBM is everything except fat (muscle, bone, organs, water). It rises with training and generally declines with severe calorie deficits.
- Body fat % from the U.S. Navy method is a quick estimate. For precision, use DEXA or multi-compartment methods.
- BSA is common in clinical dosing and metabolic estimates. It isn’t a fitness score.
- Who it’s for: lifters, athletes, and anyone tracking composition alongside weight change.
How this calculator works
Formulas, steps & assumptions
LBM (Boer): men: 0.407·W(kg) + 0.267·H(cm) − 19.2; women:0.252·W + 0.473·H − 48.3.
Body Fat % (U.S. Navy): men:86.010·log10(waist − neck) − 70.041·log10(height) + 36.76; women:163.205·log10(waist + hip − neck) − 97.684·log10(height) − 78.387 (inches).
BSA (Du Bois): 0.007184·W(kg)^0.425·H(cm)^0.725.
Assumptions: adult population, steady hydration, tape placement as described. Estimates vary with muscularity and fat distribution; use for planning, not diagnosis.
Use cases & examples
Example 1: Male, 70 in, 180 lb, no tape → LBM ≈ 136 lb
and BSA ≈ 2.00 m²
Example 2: Female, 165 cm, 68 kg with tape → body fat ≈ 27.2% and LBM ≈ 46.9 kg
Example 3: Tracking recomposition—weight stable but LBM rising suggests muscle gain with fat loss.
Lean Body Mass Calculator: Estimate LBM, Body Fat Percentage, and BSA with Practical Accuracy
A practical lean body mass calculator helps you look beyond the scale. Body weight alone can’t tell you whether changes come from fat, muscle, or water. By combining Boer LBM, the U.S. Navy body fat method (when tape measurements are available), and Du Bois body surface area (BSA), you get a rounded picture that’s useful for training, nutrition, and health decisions. This guide explains how each formula works, when to trust the estimate, and how to use the numbers to plan your next steps—like setting protein targets, choosing a calorie deficit, or checking whether a program is moving you toward your goals.
Why LBM matters more than weight alone
Lean body mass includes muscle, bone, organs, and water—everything except fat. Two people at the same weight can have very different LBM. If your goal is performance or a leaner look, preserving (or increasing) LBM while you reduce fat is the name of the game. Tracking LBM alongside body fat percentage tells you whether a cut is too aggressive, whether protein is sufficient, and whether your training is productive. If LBM drops rapidly, it’s a sign to adjust calories, protein, recovery, or volume.
How the formulas you see here work
The Boer equations estimate LBM from height and weight with sex-specific coefficients. Accuracy is solid for general adults and easy to collect. The U.S. Navy method uses neck, waist, and (for women) hip circumferences to approximate body fat percentage via logarithms—fast and consistent when you measure in the same way each time. The Du Bois formula converts height and weight into a BSA used in clinical settings and metabolic research. None are perfect, but together they create a useful compass.
Make the numbers actionable
- Protein: 1.6–2.2 g/kg/day supports muscle during cuts and training.
- Progress checks: repeat tape measurements weekly under similar conditions.
- Training signals: rising LBM with steady weight often means recomposition.
- Patience: day-to-day water shifts are large; judge trends across weeks.
Use this LBM calculator to sanity-check your plan. If LBM is sliding while calories are low, increase protein, add resistance training, or ease the deficit. If body fat holds steady at maintenance calories, tighten intake or raise activity slightly. Small, consistent tweaks beat crash diets every time.
Lean Body Mass — FAQ
What’s a good LBM for my height?
There’s no single “good” number—compare your own trend over time and pair with performance goals.
How accurate is the U.S. Navy method?
It’s an estimate. Consistent tape placement and timing improve repeatability; DEXA is more precise.
Why does my body fat change day to day?
Hydration and gut content shift scale weight and circumferences. Judge trends over weeks, not days.
Can I gain LBM in a deficit?
New lifters and detrained athletes sometimes can; otherwise prioritize maintenance or a small surplus.
Should I use metric or imperial?
Either works—this tool converts behind the scenes so formulas get the right units.
Is BSA a fitness metric?
No—BSA is mainly clinical. It’s included for completeness and context.