Body Mass Calculator – Quick, Free, and Easy to Use
The Body Mass Calculator on Addition.site lets you instantly estimate your lean body mass (the weight of everything in your body except fat). Simply enter your current weight in kilograms, your body‑fat percentage, and click Calculate. The result appears in the text field as “X.X kg” and can be copied to the clipboard or shared on X (formerly Twitter) with a single click. Best of all it's totally free, and easy to use.
How to Use the Calculator
- Enter your data
- Weight (kg) – your total body weight.
- Height (cm) – currently not used in the calculation but kept for future updates.
-
Body Fat (%) – your body‑fat percentage (you can obtain this from skin‑fold calipers, a smart scale, or an app).
-
Click “calculate”
The script multiplies your weight by (1 – bodyFat/100) to give you the lean mass. -
View the result
The result field shows the lean mass rounded to one decimal place (e.g., “56.0 kg”). -
Copy or share
- Click the result field to copy the value to your clipboard.
- Click the “𝕏” button to post the result directly to X.
What Is Lean Body Mass?
Lean body mass (LBM) is the total mass of your body that is not fat. It includes muscle, bone, water, organs, and connective tissue. Knowing your LBM helps you:
- Track muscle gain or loss over time.
- Adjust training and nutrition plans for optimal body composition.
- Set realistic fitness goals based on your current physique.
How the Calculation Works
Lean Mass (kg) = Weight (kg) × (1 – Body Fat % ÷ 100)
For example, if you weigh 70 kg and have 20 % body fat:
70 × (1 – 20 ÷ 100) = 56.0 kg of lean mass
The calculator rounds the result to one decimal place for readability.
Use Cases
| Goal | How the calculator helps |
|---|---|
| Muscle‑building | Monitor changes in lean mass as you lift weights. |
| Weight‑loss | Distinguish between fat loss and muscle loss. |
| Body‑composition tracking | Compare lean mass across different time points or diets. |
| Nutrition planning | Adjust protein intake based on lean mass. |
Tips for Accurate Results
- Use reliable body‑fat measurements – skin‑fold calipers, DEXA scans, or calibrated smart scales provide the best accuracy.
- Keep weight consistent – measure at the same time of day and under similar conditions.
- Re‑calculate after each major change – new training regimens or diets can shift your body composition quickly.
Why This Calculator Is Great
- Free, no sign‑up required – instantly available from any device with a web browser.
- Simple interface – only three inputs and one button.
- Shareable results – easy to post your progress on social media.
- Open source – the underlying JavaScript is lightweight and easy to audit.
Use the Body Mass Calculator to gain a clearer picture of your fitness journey, set informed goals, and celebrate every lean‑mass milestone along the way. And it's free to use and share.