Lean Body Mass Calculator

How to Calculate Lean Body Mass

Lean Body Mass (LBM) is the total weight of your body minus all the weight due to your fat mass. It includes the weight of your organs, bones, muscles, and body water. Calculating LBM is crucial for understanding body composition and is often used in medical and fitness contexts.

Lean Body Mass Formulas

Several formulas are commonly used to calculate LBM:

1. Boer Formula:
   Male: LBM (kg) = (0.407 × Weight in kg) + (0.267 × Height in cm) - 19.2
   Female: LBM (kg) = (0.252 × Weight in kg) + (0.473 × Height in cm) - 48.3
2. James Formula:
   Male: LBM (kg) = (1.1 × Weight in kg) - (128 × (Weight in kg / Height in cm)²)
   Female: LBM (kg) = (1.07 × Weight in kg) - (148 × (Weight in kg / Height in cm)²)
3. Hume Formula:
   Male: LBM (kg) = (0.32810 × Weight in kg) + (0.33929 × Height in cm) - 29.5336
   Female: LBM (kg) = (0.29569 × Weight in kg) + (0.41813 × Height in cm) - 43.2933

Calculation Steps

1. Convert height to cm and weight to kg if necessary
2. Choose the appropriate formula based on gender
3. Apply each formula using the height and weight
4. Calculate the average of all formulas for a more comprehensive estimate
5. Calculate body fat percentage using the average LBM

Example Calculation

Let's calculate the LBM for a male who is 180 cm tall and weighs 80 kg.

Step 1: Apply the Boer Formula

$$\begin{align} LBM_{Boer} &= (0.407 \times 80) + (0.267 \times 180) - 19.2 \\ &= 32.56 + 48.06 - 19.2 \\ &= 61.42 \text{ kg} \end{align}$$

Step 2: Apply the James Formula

$$\begin{align} LBM_{James} &= (1.1 \times 80) - (128 \times (80 / 180)^2) \\ &= 88 - (128 \times 0.1975) \\ &= 88 - 25.28 \\ &= 62.72 \text{ kg} \end{align}$$

Step 3: Apply the Hume Formula

$$\begin{align} LBM_{Hume} &= (0.32810 \times 80) + (0.33929 \times 180) - 29.5336 \\ &= 26.248 + 61.0722 - 29.5336 \\ &= 57.7866 \text{ kg} \end{align}$$

Step 4: Calculate Average LBM

$$\begin{align} LBM_{Average} &= \frac{61.42 + 62.72 + 57.7866}{3} \\ &= 60.6422 \text{ kg} \end{align}$$

Step 5: Calculate Body Fat Percentage

$$\begin{align} Body Fat Percentage &= \frac{80 - 60.6422}{80} \times 100\% \\ &= 24.20\% \end{align}$$

Therefore, the estimated lean body mass for this person is approximately 60.64 kg, and their body fat percentage is about 24.20%.

Visual Representation

This pie chart visually represents the body composition of the person in our example calculation. It shows the proportion of lean body mass (60.64 kg) to fat mass (19.36 kg) in their total body weight of 80 kg.