About the Lean Body Mass Calculator
Lean body mass is everything you are made of except fat: muscle, bone, organs, water, and connective tissue. It is the metabolically active portion of your body, which makes it the more meaningful figure to track when the goal is losing fat rather than simply losing weight.
The formula
Boer (men): LBM = 0.407·kg + 0.267·cm − 19.2The women's equation is LBM = 0.252·kg + 0.473·cm − 48.3. The Boer formula estimates lean mass from weight and height without needing body fat measurement.
How to use this calculator
- 1Enter your Total Weight (kg). The field starts at
80, which you can overwrite. - 2Enter your Height (cm). The field starts at
178, which you can overwrite. - 3Enter your Gender (1=Male, 2=Female). The field starts at
1, which you can overwrite. - 4Read the result straight away — it recalculates as you type, so there is no button to press. Use Share to copy a link that reopens the page with your exact numbers filled in.
Worked example
| Input | Value |
|---|---|
| Total Weight (kg) | 80 |
| Height (cm) | 178 |
| Gender (1=Male, 2=Female) | 1 |
Result
Lean Body Mass: 60.9 kg (134.3 lbs)
Fat Mass: 19.1 kg
Body Fat: 23.9%
Those are the values the page loads with, so you can reproduce this result yourself and then change one field at a time to see what drives the outcome.
Understanding your result
Lean mass is what drives basal metabolic rate, since muscle and organs consume energy at rest while stored fat consumes very little. This is why preserving lean mass during a diet matters so much: lose muscle and you lower your own maintenance requirement, which is a large part of why aggressive dieting so often rebounds.
The distinction between weight loss and fat loss depends entirely on this number. Losing 5 kg of which 4 is fat is a good outcome; losing 5 kg of which 2 is muscle is not, even though the scale reads the same. Tracking lean mass alongside weight is what separates the two.
Things worth knowing
- Adequate protein — roughly 1.6 to 2.2 g per kg of body weight — protects lean mass during a calorie deficit.
- Resistance training is the strongest signal to retain muscle while dieting. Cardio alone does not provide it.
- Aggressive deficits accelerate muscle loss. Slower loss preserves more lean mass.
- Lean mass declines with age from around 30 without training, which is what drives the fall in metabolic rate.
- DEXA and bioelectrical impedance measure lean mass directly and more accurately than any formula estimate.
Frequently asked questions
What is lean body mass?+
Total body weight minus fat mass — muscle, bone, organs, water, and connective tissue. It is the metabolically active tissue that determines most of your resting energy expenditure.
Why does lean body mass matter?+
Because it drives your metabolic rate and physical function. Preserving it during weight loss keeps your maintenance calories higher and means you lose fat rather than the tissue you want to keep.
How do I preserve lean mass while dieting?+
Eat 1.6 to 2.2 g of protein per kg of body weight, train with resistance at least twice a week, and keep the deficit moderate. All three matter, and protein alone is not enough.
Is lean body mass the same as muscle mass?+
No. Lean mass includes bone, organs, and water as well as muscle. Skeletal muscle is typically about half of lean mass, so a change in lean mass is not a one-to-one change in muscle.