What is fat-free mass?

Fat-free mass (FFM) is the total mass of your body excluding all fat tissue. It is effectively the same as lean body mass (LBM) and includes muscle, bone, organs, and water.

How is fat-free mass calculated?

This tool uses the Boer (1984) formula. For men: FFM = 0.407w + 0.267h − 19.2. For women: FFM = 0.252w + 0.473h − 48.3. Where w is weight in kg and h is height in cm.

Can I use this to track muscle gain?

Yes. If your total weight stays the same but your fat-free mass increases, you have likely gained muscle and lost fat. Tracking FFM over time gives a better picture of body recomposition than weight alone.

Is my data sent to a server?

All calculations are pure JavaScript running in your browser. Our servers are not involved at any point.

Fat-free mass calculator

Fat-free mass (FFM) and lean body mass (LBM) are often used interchangeably. This calculator uses the Boer (1984) formula to estimate your fat-free mass from your weight and height. All results are shown in both kg and lbs. All calculations run locally in your browser.

Sex

Units

Weight (kg)

Height (cm)

How it works

The Boer (1984) formula estimates lean body mass from weight and height. For men: LBM = 0.407 × weight (kg) + 0.267 × height (cm) − 19.2. For women: LBM = 0.252 × weight (kg) + 0.473 × height (cm) − 48.3. Imperial inputs are converted to metric before calculation. Fat mass is calculated as total weight minus LBM, and body fat percentage as fat mass divided by total weight multiplied by 100. All arithmetic runs in JavaScript in your browser.

Processing runs in your browser

All calculations happen locally in your browser tab. Our servers are not involved at any point.

Related operations

For measuring body fat directly with circumference inputs, try the body fat calculator. To check a general weight category, use the BMI calculator. For a reference weight range tied to height, see the ideal weight calculator.

Frequently asked questions

What is fat-free mass?: Fat-free mass (FFM) is the total mass of your body excluding all fat tissue. It is effectively the same as lean body mass (LBM) and includes muscle, bone, organs, and water.
How is fat-free mass calculated?: This tool uses the Boer (1984) formula. For men: FFM = 0.407w + 0.267h − 19.2. For women: FFM = 0.252w + 0.473h − 48.3. Where w is weight in kg and h is height in cm.
Can I use this to track muscle gain?: Yes. If your total weight stays the same but your fat-free mass increases, you have likely gained muscle and lost fat. Tracking FFM over time gives a better picture of body recomposition than weight alone.
Is my data sent to a server?: All calculations are pure JavaScript running in your browser. Our servers are not involved at any point.

Fat-free mass calculator

How it works

Processing runs in your browser

Related operations

Frequently asked questions

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