Lean Body Mass Calculator

Lean body mass (LBM) is everything in your body that is not fat: your muscle, bone, water, and organs. It drives both your metabolism and your strength, which is why keeping it high is a goal for nearly everyone, whether you are losing weight or building it.

What lean body mass includes

Your body weight is simply your fat mass plus your lean mass. Most of the lean portion that you can influence is skeletal muscle, the tissue you build through training and feed with protein. More lean mass generally means a higher resting calorie burn and a stronger, more resilient body.

How it is calculated

This tool uses the Boer, James, and Hume formulas, which estimate lean mass from your height, weight, and sex. Showing all three gives you a sense of the likely range rather than a single false-precision figure.

Why it matters when dieting

The failure mode of most diets is losing muscle along with fat, which lowers metabolism and leaves you smaller but still soft. Preserving lean mass is what makes weight loss actually improve how you look and feel. The levers are enough protein, resistance training, and avoiding extreme calorie cuts.

Protecting your lean mass

SmaartCoach keeps protein high in your meal plan and programs the strength training that preserves muscle, so when the scale drops, it is fat coming off, not the muscle you worked to build.