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Lean Body Mass Calculator

Calculate your lean body mass and estimated fat mass from your body weight and body-fat percentage. The calculator shows approximately how much of your current body weight is not body fat.

1

Your Body Weight

lb
Enter your current body weight. Pounds are used as the default unit for the English calculator.
2

Body-Fat Percentage

%
Enter your measured or estimated body-fat percentage. The more accurate this input is, the more useful the result will be.

Your Estimated Lean Body Mass:

0 lb

Your result will appear after calculation.

Your Lean Body Mass Calculator Result

0
lb lean
0
lb fat
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This result is an informational estimate and is not medical or healthcare advice. Accuracy depends primarily on the accuracy of the body-fat percentage you enter.
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How Does the Lean Body Mass Calculator Work?

The Lean Body Mass Calculator estimates your lean body mass and fat mass from your body weight and body-fat percentage. Lean Body Mass (LBM) is the portion of your total body weight that is not body fat. It is important to understand that LBM is not the same as muscle mass because it also includes water, bones, organs and other non-fat tissues.

Term What does it mean? In the calculation Why does it matter?
Lean Body Mass The portion of total body weight that is not body fat. It is commonly abbreviated as LBM. Body weight − fat mass It estimates how much of your total body weight is made up of non-fat tissue.
Fat Mass The estimated amount of your total body weight that is body fat based on your body-fat percentage. Body weight × body-fat % Fat mass is subtracted from total body weight to calculate lean body mass.
Body-Fat Percentage The estimated percentage of your total body weight that is body fat. % This is the key input for the calculation, so the accuracy of the body-fat measurement directly affects the result.
Body Weight Your total body mass entered in kilograms or pounds. kg / lb Combined with body-fat percentage, it determines your estimated fat mass and lean body mass.
LBM ≠ Muscle Mass Lean body mass does not consist entirely of muscle. Muscle + water + bone + organs + other fat-free tissue A change in LBM should therefore not automatically be interpreted as the same change in muscle mass.

1. Calculate Fat Mass

The calculator first uses your body weight and body-fat percentage to estimate your fat mass. For example, at 176 lb and 20% body fat, the estimated fat mass is 35.2 lb.

2. Calculate Lean Body Mass

Your estimated fat mass is subtracted from your total body weight. In the example above, 176 lb − 35.2 lb = 140.8 lb of estimated lean body mass.

3. Interpret the Result

The result estimates how much of your total body weight is not body fat. It is not the same as skeletal muscle mass, so LBM is best used as a body-composition tracking measure.

Fat Mass Formula:
fat mass = body weight × (body-fat percentage ÷ 100)

Lean Body Mass Formula:
lean body mass = body weight − fat mass

Simplified LBM Formula:
LBM = body weight × (1 − body-fat percentage ÷ 100)

Example:
176 lb × (1 − 20 ÷ 100) = 140.8 lb lean body mass

The calculator mathematically follows directly from the body weight and body-fat percentage you enter, so the accuracy of the result depends primarily on the accuracy of your body-fat measurement or estimate. Lean body mass is not the same as muscle mass, and short-term changes in body weight can also be strongly influenced by changes in body water.

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Fitness Calculators
Lean Body Mass Calculator

Lean Body Mass Calculator estimates your lean body mass and fat mass from your body weight and body-fat percentage. Lean body mass is the portion of your total body weight that is not body fat, including muscle, water, bones and organs. The calculation uses a simple formula: body weight minus estimated fat mass. The result can be useful for tracking changes in body composition over time.

Medical Disclaimer: The calculator results and information provided in this article are for educational and informational purposes only and do not constitute medical, health, or professional advice. Always consult with a qualified healthcare provider before making any decisions related to your health, diet, or fitness goals. Individual results may vary, and this tool should not be used to diagnose or treat any medical condition.

What is lean body mass?

Lean body mass is the portion of your total body weight that is not body fat. It includes muscle, body water, bones, organs and other non-fat tissues. For this reason, lean body mass should not be treated as the same thing as muscle mass.

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How do you calculate lean body mass?

Lean body mass can be calculated by subtracting estimated fat mass from total body weight. Fat mass is calculated by multiplying body weight by your body-fat percentage. The simplified formula is LBM = body weight × (1 − body-fat percentage ÷ 100).

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What is the difference between lean body mass and muscle mass?

Lean body mass includes all of the body's non-fat tissue, not just muscle. Skeletal muscle is only one component of lean body mass. Changes in hydration, glycogen and other tissues can therefore affect lean body mass without representing an equivalent change in muscle.

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Why is lean body mass important when losing weight?

During weight loss, changes can occur in both fat mass and lean body mass. Adequate protein intake, resistance training and a sensible calorie deficit can help support the retention of lean tissue. Tracking body composition alongside body weight can therefore provide more context than the scale alone.

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How can you increase lean body mass?

Increasing lean body mass generally involves resistance training combined with adequate nutrition and recovery. Progressive resistance training provides an important stimulus for muscle growth, while sufficient protein and energy availability support the adaptation process. Consistency over time is more important than any single workout or meal.

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How accurate is a lean body mass calculator?

The mathematical calculation is straightforward, but the result is only as accurate as the body-fat percentage you provide. Different body-fat measurement methods have different levels of accuracy and can be affected by measurement conditions. For this reason, LBM is often most useful for tracking trends over time using the same measurement method and similar conditions.

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