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Body composition

Lean body mass calculator

Estimate your lean body mass, everything that is not fat, from your height, weight and sex. See your fat mass and implied body-fat percentage too, with a second formula as a cross-check.

Lean body massLive
137.6lb
Fat mass47.4 lb
Body fat · implied25.6%
Hume estimate128.6 lb

Headline uses the Boer formula; Hume is shown as a cross-check. If you know your body-fat percentage, lean mass = weight x (1 minus body fat) is more accurate than any height and weight estimate.

How it works

How lean body mass is estimated

The Boer formula predicts lean mass from your height, weight and sex using coefficients fitted to body-composition data. Your fat mass is then simply your weight minus that lean mass, and the implied body-fat percentage follows from the two.

Because it is built from height and weight alone, it cannot see how muscular you actually are. If you know your body-fat percentage from a tape estimate or a scan, multiplying it out gives a more personal number. The Hume estimate is shown so you can see how much the two methods agree.

Questions

Lean body mass questions

What is lean body mass?
Everything in your body that is not fat: muscle, bone, organs and water. It is your total weight minus your fat mass, and it is often a more useful target than the scale number alone.
How is it calculated here?
The headline uses the Boer formula, which estimates lean mass from your height, weight and sex. The Hume formula is shown as a cross-check. If you already know your body-fat percentage, the direct method (weight times one minus body fat) is more accurate.
Why does lean body mass matter?
It tracks muscle better than scale weight, and many protein and calorie targets scale with lean mass rather than total weight. Watching it over time tells you whether you are keeping muscle while losing fat.
How accurate is the estimate?
For most people it lands within a couple of pounds or a kilogram. It is a height-and-weight estimate, not a DEXA scan, so it is best for tracking change with consistent inputs.
Do you save my results?
No. Everything is calculated in your browser and nothing is stored or sent anywhere.
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