# Lean Body Mass Calculator

Calculate your lean body mass using the Boer, James, and Hume formulas. Estimate your fat-free mass and body fat percentage based on weight, height.

## What this calculates

Lean body mass (LBM) is your total body weight minus all fat mass, including muscles, bones, organs, and water. This calculator estimates your LBM using three established medical formulas to give you a comprehensive picture of your body composition.

## Inputs

- **Gender** — options: Male, Female
- **Weight** (kg) — min 20, max 300
- **Height** (cm) — min 100, max 250

## Outputs

- **LBM (Boer Formula)** (kg) — Lean body mass using the Boer formula
- **LBM (James Formula)** (kg) — Lean body mass using the James formula
- **LBM (Hume Formula)** (kg) — Lean body mass using the Hume formula
- **Estimated Body Fat %** — formatted as percentage — Estimated body fat percentage based on average LBM

## Details

Lean body mass is an important metric for understanding your body composition beyond what the scale shows. It includes everything in your body except stored fat: skeletal muscle, organs, bones, blood, water, and connective tissue. Knowing your LBM helps with setting appropriate protein intake, calorie targets, and medication dosing.

The three formulas used here each approach LBM estimation differently. The Boer formula (1984) uses a linear relationship between weight, height, and LBM. The James formula uses a quadratic approach based on the ratio of weight to height. The Hume formula (1966) is a regression-based estimate. All three are reasonably accurate for individuals of normal to moderately overweight body composition.

For very lean or very obese individuals, these formulas may be less accurate. Direct measurement methods such as DEXA scans, underwater weighing, or bioelectrical impedance analysis provide more precise body composition data. These calculator estimates are best used as a general guideline for nutritional and fitness planning.

## Frequently Asked Questions

**Q: What is the difference between lean body mass and muscle mass?**

A: Lean body mass includes all non-fat tissue: skeletal muscle, smooth muscle, cardiac muscle, bones, organs, blood, water, and connective tissue. Muscle mass is just one component of LBM. Approximately 40-50% of lean body mass is skeletal muscle in healthy adults. LBM is the broader, more clinically useful measurement for nutritional and medical calculations.

**Q: Which LBM formula is most accurate?**

A: No single formula is consistently most accurate for all individuals. The Boer formula is generally preferred for its simplicity and reasonable accuracy across a range of body types. The James formula may underestimate LBM in obese individuals. Using the average of all three formulas provides the most reliable estimate. For precise measurements, DEXA scanning is the gold standard.

**Q: Why does LBM matter for nutrition?**

A: LBM is the primary driver of your basal metabolic rate, meaning people with more lean mass burn more calories at rest. Protein requirements are also better calculated based on LBM rather than total body weight, especially for overweight individuals. A general recommendation is 1.6-2.2 grams of protein per kilogram of LBM for those engaged in strength training.

**Q: Can I increase my lean body mass?**

A: Yes, lean body mass can be increased primarily through resistance training combined with adequate protein intake and a slight caloric surplus. Beginners can gain 0.5-1 kg of muscle per month with proper training and nutrition. The rate of muscle gain decreases with training experience. Adequate sleep and recovery are also critical for muscle growth.

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Source: https://vastcalc.com/calculators/health/lean-body-mass
Category: Health & Fitness
Last updated: 2026-04-21