If you know body-fat percentage
The calculator multiplies your weight by that percentage to estimate fat mass. What remains is lean mass.
Sources last read
Body composition · free calculator
Lean body mass calculator
Enter your current weight and one body-composition number: either body-fat percentage or lean mass. You will see estimated lean mass, fat mass and body-fat percentage. The calculator does not measure your body.
Source: body-composition sources, read 2026-08-21
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Estimate lean mass and fat mass
Keep both mass values in the same unit. You can switch units above without retyping them.
Your estimate
Add both numbers
This calculator does not measure body fat
How the math works
It separates the weight you entered into two parts
If you know lean mass
The calculator subtracts lean mass from your weight to estimate fat mass, then shows that amount as a percentage of your weight.
Use the same measurement method when you compare results
Different methods can give different answers. A home scale and a body scan may not agree, even on the same day. This tool repeats the number you provide. It does not decide what your result should be or whether a change is healthy.
Useful next steps
Put the number in context
- Percentage of Body Fat Assessment Using Bioelectrical Impedance Analysis and Dual-Energy X-ray Absorptiometry in a Weight Loss Program for Obese or Overweight Chinese Adultsretrieved 2026-08-21human study
- Nutritional priorities to support GLP-1 therapy for obesity: A joint advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association, and the Obesity Societyretrieved 2026-08-21joint advisory