Reviewed by James Okafor, ACSM-CPT, CSCS, MS Exercise Science
Last updated May 2025
Lean Body Mass Calculator — Fat-Free Mass Estimate
The CalcNest Lean Body Mass Calculator estimates your fat-free mass using the Boer formula, which is considered the most accurate equation-based method for predicting lean body mass from height and weight alone. Lean body mass includes everything in your body except stored fat — muscles, bones, organs, water, and connective tissue. Knowing your lean body mass is essential for calculating accurate protein requirements, assessing body composition changes, and setting realistic body recomposition goals.
You might also need: Body Fat Calculator · BMI Calculator · Protein Calculator
How the Lean Body Mass Calculator Works
Lean body mass (LBM) represents everything in your body except fat — muscles, bones, organs, water, and connective tissue. This calculator uses the Boer formula (1984), which estimates LBM from weight and height with gender-specific coefficients.
Knowing your LBM is valuable for setting protein intake targets (protein should be based on lean mass, not total weight), calculating more accurate calorie needs, monitoring muscle gain during a bulk, and ensuring you're losing fat rather than muscle during a cut.
The visual body composition bar shows the split between lean mass and fat mass, making it easy to understand your current body composition at a glance.
The Boer Formula
Male LBM (kg) = (0.407 × Weight) + (0.267 × Height) − 19.2
Female LBM (kg) = (0.252 × Weight) + (0.473 × Height) − 48.3
Fat Mass = Total Weight − LBM
Body Fat % = (Fat Mass ÷ Total Weight) × 100
Body Composition Measurement Methods
| Method | Accuracy | Cost |
|---|---|---|
| DEXA Scan | ±1-2% | $75-150 |
| Hydrostatic Weighing | ±1.5-2.5% | $50-100 |
| BIA Scale | ±3-5% | $30-200 |
| Skinfold Calipers | ±3-4% | $10-30 |
| Boer Formula (this calc) | ±3-5% | Free |
Frequently Asked Questions
Why is lean body mass important?
Lean body mass is important because it determines your basal metabolic rate — more lean mass means more calories burned at rest. It is also a better indicator of health and fitness than total body weight alone. Tracking lean body mass over time tells you whether you are losing fat, gaining muscle, or both during body recomposition, which total body weight cannot reveal.
What is the Boer formula?
The Boer formula estimates lean body mass using height and weight. For men: LBM = 0.407 × weight(kg) + 0.267 × height(cm) - 19.2. For women: LBM = 0.252 × weight(kg) + 0.473 × height(cm) - 48.3. This formula was validated in a 1984 study and is considered one of the most accurate predictive equations when body fat measurements are not available.
How do I use lean body mass to calculate protein needs?
Many sports nutritionists recommend setting protein targets based on lean body mass rather than total body weight, especially for overweight or obese individuals. A common recommendation is 2.0-2.5 grams of protein per kilogram of lean body mass. This approach prevents overestimating protein needs for those with significant body fat and provides more accurate targets for everyone.
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Disclaimer: Lean body mass estimates using the Boer formula are approximations. Accuracy varies based on individual body composition, muscle mass, and hydration levels. For precise body composition analysis, consider a DEXA scan or hydrostatic weighing. This calculator is not intended to diagnose or treat any health conditions.