Health

Lean Body Mass Calculator

Estimate your lean body mass, body fat, and Fat-Free Mass Index using the Boer and Hume formulas

Quick Answer:For a 70 kg male at 175 cm, lean body mass is approximately 57-59 kg using the Boer and Hume formulas in 2026, representing about 82-84% of total body weight.

Your Details

Lean Body Mass (Boer)

Calculating... kg

Hume LBM

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Body Fat Mass

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Estimated Body Fat %

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FFMI (Fat-Free Mass Index)

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Composition Breakdown

Lean Mass (Boer)-- kg
Lean Mass (Hume)-- kg
Fat Mass-- kg

Expert Insight 2026 Pro Tip

Lean body mass is the single best predictor of your true calorie needs and metabolic health. Unlike total weight, LBM directly drives basal metabolic rate since muscle tissue burns 6-7 calories per pound at rest versus 2-3 for fat. The Fat-Free Mass Index (FFMI) is a more meaningful progress metric than BMI for anyone who strength trains, as it separates muscle gains from fat changes. An FFMI above 20 for men or 17 for women indicates meaningful training adaptation.

Frequently Asked Questions

What is lean body mass and how does it differ from muscle mass?

Lean body mass (LBM) encompasses everything in your body that is not fat, including muscles, bones, organs, blood, water, and connective tissue. It differs from muscle mass in that muscle is only one component of lean body mass. For an average adult, skeletal muscle typically accounts for about 40-50% of lean body mass, with the remainder consisting of organ weight, bone mass, blood volume, and body water. Understanding your LBM is valuable because it drives your metabolic rate more accurately than total body weight. Two people weighing the same but with different LBM values will have significantly different caloric needs. LBM also serves as a better predictor of drug dosing requirements and athletic potential than total body weight alone, which is why clinicians and coaches track it separately.

What is a good Fat-Free Mass Index (FFMI) score?

The Fat-Free Mass Index (FFMI) provides a height-normalized measure of lean body mass, similar to how BMI normalizes total weight. For men, an FFMI of 18-20 is average for untrained individuals, while 20-22 indicates regular strength training, and 22-25 represents advanced athletic development. An FFMI above 25 is extremely rare naturally and is often associated with anabolic steroid use, though genetic outliers do exist. For women, average FFMI ranges from 14-17 for untrained individuals and 17-20 for well-trained athletes. Research by Kouri and colleagues established 25 as the approximate natural limit for male FFMI based on studies of pre-steroid era athletes. Tracking FFMI over time provides a more meaningful measure of muscle-building progress than body weight alone.

How accurate are the Boer and Hume lean body mass formulas?

The Boer and Hume formulas provide reasonable estimates of lean body mass based on height and weight, but they have inherent limitations since they cannot directly measure body composition. Both formulas were developed through regression analysis of populations measured with more precise methods like underwater weighing. The Boer formula, published in 1984, tends to produce slightly higher estimates and is considered more accurate for average-build individuals. The Hume formula from 1966 provides marginally lower estimates and may be slightly better for individuals with higher body fat percentages. For most adults with typical body compositions, both formulas agree within 1-3 kg of each other. However, neither formula accounts for individual variation in bone density, muscle mass, or hydration status, so they should be viewed as approximations rather than precise measurements.

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