Estimate Your Lean & Muscle Metrics
Enter your details to calculate BMI, lean body mass, FFMI, and an estimated skeletal muscle mass.
This tool is for education only and does not replace clinical body composition testing.
What this body muscle calculator tells you
Most people track only body weight, but weight alone can hide what is really changing in your body. This calculator helps you see deeper metrics that matter for physique and performance: lean body mass, fat mass, fat-free mass index (FFMI), and an estimate of skeletal muscle.
If you enter body fat percentage, the calculator uses that to estimate your lean mass directly. If you leave body fat blank, it uses the Boer equation based on sex, height, and weight to provide a practical estimate.
How to use the results
1) BMI
BMI is useful for population trends but limited for individuals with above-average muscle mass. Use it as context, not as your only fitness metric.
2) Lean Body Mass (LBM)
LBM is your total body weight minus fat mass. If your training and nutrition are effective, this number tends to trend upward over months, even if scale weight stays stable.
3) FFMI
FFMI (fat-free mass index) adjusts lean mass for height, giving a better picture of muscularity between people of different sizes.
4) Estimated Skeletal Muscle
This value is an estimate derived from lean body mass. It is not as accurate as DEXA or MRI, but it gives a useful direction for tracking progress over time under consistent conditions.
Best practices for accurate tracking
- Measure at the same time of day, ideally morning after using the bathroom.
- Use the same scale and method each time.
- Track weekly trends instead of daily fluctuations.
- Recheck body fat monthly if possible for better LBM estimates.
Training and nutrition tips to improve muscle metrics
- Progressive overload: Aim to improve reps, load, or quality each week.
- Protein intake: A practical range is ~1.6 to 2.2 g per kg body weight daily.
- Sleep: 7-9 hours supports recovery and hormone function.
- Consistency: Small weekly improvements compound into major physique changes.
Important limitations
No online calculator can perfectly measure muscle. Hydration, glycogen, and measurement error can all affect outputs. Use this page as a decision-support tool, not a diagnosis tool. If you need medical-grade assessment, consider clinical testing.