Use total body weight if:
- • Body fat is below ~25% (men) or ~32% (women)
- • You don't know your body fat %
- • You want a simple, conservative target
Your body. A little more context.
Lean Body Mass Calculator
Calculate your lean body mass and get protein targets based on lean mass rather than total body weight — the approach used by sports dietitians for clients with higher body fat.
Free to use · No sign-up needed
Understand what makes up your weight.
From composition to planningYour lean mass.
Your protein starting point.
Your protein starting point.
3 formula options
Body fat % override
Protein targets by goal
Body composition breakdown
YOUR LEAN MASS STARTING POINT
A fuller picture of your body weight.
Enter your details. Choose a formula.
See lean mass and protein ranges.
FROM LEAN MASS TO PROTEIN PLANNING
Why LBM Matters for Protein Calculations
Most protein recommendations are given in grams per kilogram of total body weight. For lean individuals, this works well. But for someone who is 100 kg with 40% body fat, their lean mass is only 60 kg. Basing protein on 100 kg would suggest up to 220 g/day (at 2.2 g/kg) — significantly more than their lean tissue needs.
Using LBM as the basis for protein calculations corrects for this. The evidence shows that protein needs scale with metabolically active tissue, not fat mass. Using LBM (or an adjusted body weight) produces more accurate targets for people with body fat above approximately 25–30%.
When to Use LBM vs Total Body Weight
Use LBM if:
- • Body fat is above 25–30%
- • You have a body fat measurement you trust
- • You want the most accurate protein target
UNDERSTAND THE METHOD
LBM Formula Comparison
Scroll to compare
| Formula | Best For | Notes |
|---|---|---|
| Boer | General use (recommended default) | Best average accuracy in most adult populations |
| James | Lighter, shorter individuals | Can underestimate LBM in obese individuals |
| Hume | Alternative when other formulas seem off | Uses slightly different weight/height coefficients |
| Body Fat % (direct) | Anyone with a reliable BF% measurement | Most accurate — always use this if available |
CLEARER ANSWERS ABOUT LEAN MASS
Frequently Asked Questions
What is lean body mass?
Lean body mass (LBM) is the weight of everything in your body except fat: muscle, bone, organs, water, and connective tissue. It is calculated by subtracting your fat mass from your total body weight. LBM is a more precise basis for protein calculations than total body weight, especially for people with higher body fat percentages.
Why use lean body mass for protein calculations?
Protein needs are driven by metabolically active tissue — primarily muscle. Fat tissue has very low protein turnover. For someone with high body fat (>30%), basing protein intake on total body weight over-estimates needs. Using LBM or an adjusted body weight gives a more accurate, appropriate protein target. For lean individuals, total body weight and LBM produce similar results.
Which LBM formula is most accurate?
If you know your body fat percentage (from DEXA scan, BodPod, or calipers), entering it directly gives the most accurate LBM. Among prediction formulas, the Boer formula generally has the smallest error in population studies. The James and Hume formulas are alternatives with slightly different characteristics. All three are approximations; accuracy varies by body composition and ethnicity.
What is the difference between LBM and fat-free mass?
In most practical contexts, LBM and fat-free mass (FFM) are used interchangeably. Technically, LBM includes essential fat (found in the brain, nerves, and cell membranes), while FFM excludes all fat. The difference is small and clinically insignificant for nutrition planning purposes.
How do I measure my body fat percentage accurately?
From most to least accurate: DEXA scan (dual-energy X-ray absorptiometry), hydrostatic weighing, BodPod (air displacement), multi-site skinfold calipers (technician-measured), bioelectrical impedance (BIA scales/devices). BIA consumer devices are convenient but can vary by ±3–5%. DEXA is considered the gold standard and is often available at sports medicine clinics.
Disclaimer: LBM estimates are approximations. Body composition measurements vary based on hydration, measurement method, and individual factors. Consult a healthcare professional for clinical body composition assessment.