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Lean Body Mass Calculator

Calculate your lean body mass (LBM) using 4 scientific formulas (Boer, James, Hume, Peters). Track your fat-free mass to monitor body composition changes.

What Are Lean Body Mass and FFMI?

Lean body mass (LBM) is everything in your body that is not fat: muscles, bones, organs, water, and connective tissue. Knowing your LBM helps you understand how much of your weight is functional tissue versus stored energy. The Fat-Free Mass Index (FFMI) takes lean body mass a step further by normalising it to your height, similar to how BMI normalises total weight. FFMI is calculated as lean mass in kilograms divided by height in metres squared. An FFMI of 18 to 20 is average for men, 20 to 22 indicates above-average muscularity, and values above 25 are extremely rare without performance-enhancing substances. For women, typical values are lower by about 3 to 5 points.

What FFMI Can You Achieve Naturally?

Research into natural bodybuilders and athletes suggests that an FFMI of around 25 represents the upper limit for most drug-free men, with exceptional genetics occasionally reaching 26 to 27. For women, the natural ceiling is generally around 21 to 22. These numbers are useful benchmarks for setting realistic physique goals. If someone claims a natural FFMI well above 25, it may warrant scepticism. FFMI is also a valuable tool for tracking progress during a bulk or cut: if your FFMI increases during a surplus, you are likely gaining muscle, and if it holds steady during a deficit, you are successfully preserving lean mass while losing fat.

Frequently Asked Questions

How do I calculate my lean body mass at home?▼
The simplest method is to estimate your body fat percentage using the Navy tape measure formula, then subtract your fat mass from your total weight. For example, if you weigh 80 kg and have 20 percent body fat, your fat mass is 16 kg and your lean body mass is 64 kg.
What is a good FFMI?▼
For men, an FFMI of 20 to 22 indicates solid muscularity and regular training. Values of 22 to 25 represent advanced, well-developed physiques. Anything above 25 is elite-level and extremely rare naturally. For women, add roughly 3 to 5 points lower across the same categories.
What is the difference between lean mass and dry mass?▼
Lean body mass includes everything that is not fat, including water. Dry lean mass or dry mass refers to lean tissue minus water content, essentially just muscle, bone, and organs. Since water can fluctuate significantly day to day, lean body mass is more commonly used as a practical measurement.

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