What Is Fat-Free Mass Index?
Fat-free mass index is a body-composition score that compares estimated lean tissue with height. Lifters use it because body weight alone cannot separate muscle, bone, water, and fat.
FFMI Formula
The calculator estimates fat-free mass as body weight multiplied by one minus body-fat percentage. FFMI is fat-free mass in kilograms divided by height in meters squared.
Normalized FFMI Formula
Normalized FFMI uses the common height adjustment: FFMI + 6.3 x (1.8 - height in meters). This helps compare lifters who are much shorter or taller than average.
How to Read Your Score
Use normalized FFMI as the main comparison score, then look at fat-free mass, fat mass, body-fat percentage, and strength trends together.
Why Body-Fat Accuracy Matters
Small body-fat errors can shift FFMI noticeably. Use the same body-fat method over time and avoid treating one measurement as final proof.
FFMI vs BMI
BMI uses total body weight, while FFMI uses estimated fat-free mass. That makes FFMI more useful for muscular people, but it still depends on estimated body fat.
Use FFMI With Strength Data
FFMI is more useful when paired with tracked lifts, estimated one-rep max trends, and progressive overload targets.
Track Lean-Mass Progress
Bazu helps you connect body-composition goals with the training work that actually drives muscle gain: hard sets, PRs, routines, and recovery-aware progression.
How the FFMI calculator works
Bazu uses the common fat-free mass index workflow used by public FFMI calculators: estimate lean mass from body weight and body-fat percentage, divide by height squared, then show a height-normalized score.
- Step 1Convert weight to kilograms and height to meters when needed.
- Step 2Calculate fat mass as weight x body-fat percentage.
- Step 3Calculate fat-free mass as weight minus fat mass.
- Step 4Calculate FFMI as fat-free mass in kg / height in meters squared.
- Step 5Calculate normalized FFMI as FFMI + 6.3 x (1.8 - height in meters).
FFMI score ranges
These ranges are practical training categories, not medical cutoffs. Use normalized FFMI together with body-fat accuracy, training history, and strength progress.
| Group | Normalized FFMI guide |
|---|---|
| Men | 18-20 average, 20-22 athletic, 22-25 advanced, 25+ very high |
| Women | 15-17 average, 17-19 athletic, 19-21 advanced, 21+ very high |
Related reading
Go deeper on the training ideas behind this calculator.
Progressive Overload for Beginners
Learn how to add reps, weight, and volume in a way your body can recover from.
Read guideHow Bazu Calculates Personal Records
See how Bazu handles load PRs, rep PRs, bodyweight PRs, and estimated 1RM.
Read guideBest Free Workout Tracker for Strength Training
See how Bazu tracks workouts, PRs, routines, history, and training trends.
Read guideSpot PRs and Training Trends Faster
Use weekly top sets and simple checkpoints to make strength progress easier to see.
Read guideFormula references
These references informed the formula, height adjustment, and accuracy caveats used on this page.
FFMICalculator.org, FFMI formula
Public FFMI calculator reference showing fat-free mass, raw FFMI, and height-adjusted FFMI formulas.
View referenceMenno Henselmans, FFMI calculator methodology
Discussion of FFMI, height adjustment, natural muscular potential, and major accuracy caveats for body-composition estimates.
View referenceFFMI calculator FAQ
What is FFMI?
FFMI stands for fat-free mass index. It compares estimated fat-free mass with height, similar to how BMI compares total body weight with height.
How do you calculate FFMI?
First estimate fat-free mass from body weight and body-fat percentage. Then divide fat-free mass in kilograms by height in meters squared.
What is normalized FFMI?
Normalized FFMI adjusts the raw FFMI score toward a 1.8 meter reference height so very short and very tall lifters can be compared more fairly.
What body-fat percentage should I enter?
Use your best current estimate from a consistent method. FFMI is highly sensitive to body-fat accuracy, so treat the result as a planning estimate.
Is FFMI better than BMI?
FFMI can be more useful for lifters because it separates estimated lean mass from fat mass. BMI still describes total body mass relative to height.
What is a good FFMI?
A good FFMI depends on sex, training history, and body-fat accuracy. For men, the low 20s often indicate an athletic build; for women, the high teens are often athletic.
Can FFMI prove someone is natural?
No. Very high FFMI can be a useful discussion point, but it cannot prove drug use or natural status because body-fat estimates and genetics vary.
Is this FFMI calculator free?
Yes. The calculator is free, runs in your browser, and does not require a login.
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Turn body-composition goals into training progress.
Bazu tracks workouts, PRs, estimated 1RM, routines, and progressive overload targets so your lean-mass goals are connected to the work you do in the gym.
Looking for muscle-potential estimates too? Try the natural muscle gain calculator.