FFMI Calculator
Fat free mass index with the height-normalised adjustment.
Reviewed by the Calculation Machine team · Updated 24 October 2026 · How we check our maths
Your values
ⓘ Live results
- Adjusted FFMI
- 21.58
- Raw FFMI
- 21.46
- Lean body mass
- 68 kg
- Fat mass
- 12 kg
- Rating
- above average
Working
- 1lean 68 kg / 1.78^2 = 21.46
- 2adjusted = 21.46 + 6.1 x (1.8 - 1.78) = 21.58
Quick answer
FFMI (fat-free mass index) is lean body mass in kilograms divided by height in meters squared. Adjusted FFMI adds 6.1 × (1.8 − height in m) to correct for height. An 80 kg, 1.78 m person at 15% body fat has 68 kg of lean mass, an FFMI of 21.46 and an adjusted FFMI of 21.58.
What the FFMI calculator does
This calculator works out your fat-free mass index — a measure of how much muscle, bone and other non-fat tissue you carry for your height. Enter body weight, height and body fat percentage to get adjusted FFMI, raw FFMI, lean mass, fat mass and a rating.
FFMI is used by lifters and coaches to track muscle gain over months, and in research to compare muscularity between people of different sizes. It fixes the main weakness of BMI: two people with the same BMI can have very different FFMI if one carries more muscle and the other more fat.
The result is only as good as your body fat estimate. A DEXA scan is the most consistent; calipers, the Navy tape method and smart scales are fine for tracking trends if you stick to one. The ratings shown are based on research in men; women typically score a few points lower for a similar training level.
The formula
lean mass = weight × (1 − BF ÷ 100) FFMI = lean mass ÷ h² adjusted FFMI = FFMI + 6.1 × (1.8 − h)
| Symbol | Meaning | Unit |
|---|---|---|
| weight | Body weight | kg |
| BF | Body fat percentage | % |
| h | Height (cm ÷ 100) | m |
| 6.1 | Height-correction slope from the original study | kg/m² per m |
The index and the height adjustment come from Kouri et al. (1995), who measured 157 male athletes and found that drug-free lifters rarely exceeded an adjusted FFMI of about 25. The adjustment normalizes everyone to a height of 1.8 m, because taller people tend to have slightly higher FFMI at the same build. For people near 1.8 m tall, raw and adjusted values are almost the same.
Worked examples
Regular gym-goer
A man who has trained for a couple of years: 80 kg, 178 cm, 15% body fat.
Inputs
- Body weight80 kg
- Height178 cm
- Body fat15 %
Result
- Adjusted FFMI21.58
- Raw FFMI21.46
- Lean body mass68 kg
- Fat mass12 kg
- Ratingabove average
Adjusted FFMI 21.58 is above average. Adding 3–4 kg of lean mass at the same body fat would move him into the 22–25 band.
Tall, advanced lifter
A 185 cm lifter weighing 95 kg at 12% body fat.
Inputs
- Body weight95 kg
- Height185 cm
- Body fat12 %
Result
- Adjusted FFMI24.12
- Raw FFMI24.43
- Lean body mass83.6 kg
- Fat mass11.4 kg
- Ratingexcellent
Raw FFMI is 24.43 but the adjusted figure is 24.12, because the height correction lowers scores above 1.8 m. That is close to the level Kouri et al. saw as a typical natural ceiling.
Shorter woman who strength trains
A 165 cm woman weighing 62 kg at 22% body fat.
Inputs
- Body weight62 kg
- Height165 cm
- Body fat22 %
Result
- Adjusted FFMI18.68
- Raw FFMI17.76
- Lean body mass48.36 kg
- Fat mass13.64 kg
- Ratingaverage
Adjusted FFMI is 18.68, rated "average" on the male-based scale. For a woman this reflects a well-muscled build, so compare it with your own earlier readings rather than the label.
FFMI ranges used by this calculator
These bands describe adjusted FFMI for men. They are rough guides for interpreting progress, not medical categories.
| Adjusted FFMI | Rating | Typical description |
|---|---|---|
| Below 18 | Below average | Little or no resistance training |
| 18 – 20 | Average | Typical untrained to lightly trained build |
| 20 – 22 | Above average | Noticeably muscular, regular training |
| 22 – 25 | Excellent | Advanced lifter after years of training |
| 25 and above | Very high | Rare without exceptional genetics or drugs |
How body fat errors change your FFMI
Because FFMI depends entirely on lean mass, a body fat reading that is off by 5 percentage points shifts the result by more than a full point. For the default 80 kg, 1.78 m person, 5% of body weight is 4 kg, and 4 ÷ 1.78² ≈ 1.3 FFMI points.
- Measure with the same method, under the same conditions (morning, before eating), each time.
- Bioimpedance scales swing with hydration; one glass of water or a salty meal can move the reading.
- Watch the trend over months: FFMI rising while body fat holds steady is a reliable sign of muscle gain. A separate lean body mass calculator can estimate lean mass from height and weight alone if you have no body fat figure.
FFMI versus BMI
BMI divides total weight by height squared, so it rises whether you add fat or muscle. FFMI uses the same height scaling but only counts fat-free mass. A 1.78 m, 90 kg man has a BMI of 28.4 either way, but at 12% body fat his FFMI is about 25 and at 30% it is about 19.9 — very different bodies. Pair FFMI with your body recomposition plan to see whether a phase is building muscle or just losing fat.
How to use the FFMI Calculator
- 1Enter body weight in kilograms (pounds ÷ 2.2046), ideally measured in the morning.
- 2Enter height in centimeters (inches × 2.54).
- 3Enter body fat percentage from a scan, calipers or tape method, using the same method each time.
- 4Read adjusted FFMI as your headline number, and check lean and fat mass to see what is driving it.
Frequently asked questions
What is a good FFMI?
For men, an adjusted FFMI of 20–22 is above average and 22–25 reflects years of serious training. Untrained men are often around 17–19.
What is the natural FFMI limit?
In the 1995 Kouri study, drug-free male athletes rarely exceeded an adjusted FFMI of about 25. It is a statistical boundary, not a hard rule — a few people with exceptional genetics exceed it naturally.
What is the difference between FFMI and adjusted FFMI?
Adjusted FFMI adds 6.1 × (1.8 − height in m) to the raw score to compare people of different heights fairly. It lowers scores for people over 1.8 m and raises them for shorter people.
Does FFMI work for women?
The formula works the same way, but the reference ranges come from studies of men. Women typically have lower FFMI at a similar training level, so compare your own readings over time.
How fast can FFMI increase?
It depends on how much lean mass you add: at 1.78 m tall, every 3.2 kg of lean mass is one FFMI point. Beginners gain fastest in their first year; after several years progress slows to a fraction of a point a year.
References
- Fat-free mass index in users and nonusers of anabolic-androgenic steroids (Kouri et al., 1995) — Clinical Journal of Sport Medicine
About this calculator
- Built and reviewed by the Calculation Machine team · How we build and test calculators
- Last reviewed: October 24, 2026
- Report an error