FFMI / Lean body mass calculator
Your lean body mass (muscle, bone, organs and water), your fat mass, and the fat-free mass index, which scales lean mass to height so that unlike BMI it tracks how much muscle you carry. The normalised figure adjusts to a 1.8 m reference so people of different heights compare on one scale.
FFMI & Lean Body Mass Calculator
Lean body mass is bodyweight minus fat mass: weight × (1 − body fat percentage). Fat-free mass index (FFMI) divides it by height in metres squared, normalised to a 1.8 metre reference height. Most trained men sit between 19 and 22, with a natural ceiling near 25; for women the ceiling is about 21.5. Unlike BMI, FFMI measures muscularity rather than total bodyweight.
Lean mass is everything that isn't fat: muscle, bone, organs and water.
Method notes (3)
- FFMI is only as good as the body-fat % input — DEXA/BIA are more reliable than visual estimates. Consider running estimate_body_fat (navy method) if you only have circumferences.
- Categories use the normalized FFMI (height-adjusted to 1.8m). Boundaries are from Kouri et al. 1995 — population-level reference points; individual variation is large.
- The frequently-quoted ~25 'natural ceiling' for men is the normalized FFMI value, not the raw one.
Metric or imperial · runs the same code as the app · nothing is sent anywhere
How it works
FFMI = fat-free mass / height², where fat-free mass is weight × (1 − body fat %). The normalised version adds 6.1 × (1.8 − height in m) so a short lifter and a tall one can be compared.
Category boundaries come from Kouri et al. 1995, a population study of natural and steroid-using lifters. The widely quoted ceiling of about 25 for men is the normalised figure, not the raw one, and it is a population reference rather than a hard biological wall.
The result is only as good as the body-fat input. A visual guess can move FFMI by a full point, so use a DEXA, a BIA scale or at least the Navy tape method.
Common questions
What FFMI is achievable naturally?
Kouri's data puts the practical natural ceiling near a normalised FFMI of 25 for men and about 21.5 for women. Most trained lifters sit between 19 and 22. Crossing 25 is uncommon without unusually favourable genetics or pharmacology.
What is the difference between FFMI and normalised FFMI?
Raw FFMI divides lean mass by height squared, which still slightly favours shorter people. The normalised figure adjusts everyone to a 1.8 m reference height so the categories apply evenly.
Is lean body mass the same as muscle mass?
No. Lean mass includes bone, organs, skin and water as well as muscle. Skeletal muscle is typically 40 to 50 percent of lean mass, so a lean-mass gain is not all muscle.
Is FFMI better than BMI?
For anyone who trains, yes. BMI counts all mass the same, so muscle pushes you into the overweight band. FFMI looks only at lean mass, which is what you are actually trying to build.
The other calculators
Body composition
What you are made of, and what you could be.
- BMI calculatorBody mass index is weight over height squared.BMI
- Ideal weight calculatorFour classic formulas that predict a target weight from height and sex alone.Ideal weight
- Body fat calculatorThree ways to estimate body fat without a DEXA scan.Body fat
- Maximum muscular potential calculatorWrist and ankle circumference are proxies for skeletal frame size, and frame size predicts how much muscle you can ultimately carry.Max potential
- Ideal body proportions calculatorClassical proportions scale every girth from the wrist, because wrist size tracks your skeletal frame and barely changes with training or fat.Ideal proportions
- Body shape calculatorClassifies your body shape from a few tape measurements: hourglass, spoon, triangle, rectangle and the rest for women, V-taper to oval for men.Body shape
Energy
What you burn, and what to eat against it.
- TDEE, BMR & macro calculatorYour total daily energy expenditure is what you burn across a whole day, training included.TDEE, BMR & macros
- Calorie deficit calculatorPick a goal weight and a pace.Calorie deficit
- Water intake calculatorA daily drinking target from your bodyweight, with extra for training and hot weather.Water intake
Strength
What you lift, and how it ranks.
- One-rep max calculatorEstimate a maximum from a set you have actually done, without the risk of testing a true single.One-rep max
- RPE calculatorRate of perceived exertion turns how hard a set felt into numbers.RPE
- Strength level calculatorRank any lift against population strength standards for your bodyweight and sex, with an optional age adjustment.Strength level
- Powerlifting score calculatorRaw totals favour heavier lifters, so powerlifting uses coefficients to compare across bodyweight.Wilks & DOTS
- Strength symmetry calculatorComparing raw numbers across different lifts tells you nothing, because a 200 kg deadlift and a 100 kg bench are not equivalent achievements.Symmetry
- Barbell plate calculatorTells you what to hang on each side of the bar for a target weight, and whether the number is reachable at all with standard plates.Plate loading
- Warm-up sets calculatorA ramp from the empty bar to your top set: the weight gets heavier while the reps get fewer, so you arrive warm but not tired.Warm-up sets
- Training volume calculatorEnter up to three exercises with sets, reps and load.Training volume
Cardio & burn
Aerobic fitness and the cost of a session.
- VO₂max & heart rate zone calculatorTwo answers from the same three numbers.VO₂max & HR zones
- Steps to calories calculatorTurns a step count into distance and calories using your stride and bodyweight, and shows how it compares with the daily step range linked to better health at your age.Steps → calories
- Workout calorie calculatorEstimates the energy cost of an activity from its metabolic equivalent, your bodyweight and how long you did it.Activity burn
- Lifting calorie calculatorMost calculators give weight training a flat per-hour figure.Lifting burn
These numbers are more useful when something tracks them.
The app runs this same maths against your logged weigh-ins, meals and sessions, so the figure updates itself instead of being a one-off.
Start free