FFMI Calculator
Work out your fat-free mass index (FFMI) and height-normalized FFMI from height, weight and body fat percentage, in metric or US units.
Results
| Item | Value |
|---|
Quick Answer
FFMI = fat-free mass in kg ÷ height in meters squared. For an 80 kg man who is 1.80 m tall with 15% body fat, fat-free mass is 68 kg and FFMI is 68 ÷ 1.8² = 21.0. Kouri and colleagues (1995) added 6.3 × (1.80 − height) to compare people of different heights, and found that men who had not used steroids reached a limit of about 25.
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Table of Contents
- FFMI Calculator
- Quick Answer
- Related Calculators
- How This FFMI Calculator Works
- How to Use the FFMI Calculator
- FFMI Formulas
- Key Terms
- Worked Example
- Real-Life Examples
- FFMI vs BMI
- FFMI by Height and Lean Mass
- What the FFMI Study Found
- Common Mistakes to Avoid
- Frequently Asked Questions
- References & Sources
How This FFMI Calculator Works
Fat-free mass index measures how much lean mass (muscle, bone, organs and water) you carry for your height. Enter your weight, height and body fat percentage. The calculator finds your fat-free mass, divides it by your height in meters squared, and also gives the normalized FFMI, which adjusts the value to a height of 1.80 m so tall and short people can be compared.
Quick explanation: FFMI is like BMI, but it leaves out body fat.
- BMI counts all weight, so a muscular person can look overweight.
- FFMI counts only lean mass, so it rewards muscle, not fat.
- Around 25 was the upper limit for men in the 1995 study who had not used steroids.
How to Use the FFMI Calculator
- Choose metric or US units.
- Enter your weight and height.
- Enter your body fat percentage from a measurement or estimate.
- Press Calculate.
- Read your FFMI, normalized FFMI, fat-free mass and fat mass.
FFMI Formulas
- Fat-free mass: weight × (1 − body fat % ÷ 100)
- FFMI: fat-free mass (kg) ÷ height (m)²
- Normalized FFMI: FFMI + 6.3 × (1.80 − height in m)
- US units: 1 lb = 0.45359237 kg and 1 in = 0.0254 m
Key Terms
- Fat-free mass: everything in the body except fat: muscle, bone, organs and water.
- FFMI: fat-free mass index, lean mass divided by height squared.
- Normalized FFMI: FFMI adjusted to a height of 1.80 m with 6.3 × (1.80 − height).
- Body fat percentage: the share of body weight that is fat.
- DEXA: a low-dose X-ray scan that measures fat, lean mass and bone.
Worked Example
A man is 5 ft 10 in (70 inches) tall, weighs 185 lb and has 12% body fat.
- Weight = 185 × 0.4536 = 83.9 kg; height = 70 × 0.0254 = 1.778 m
- Fat-free mass = 83.9 × 0.88 = 73.8 kg
- FFMI = 73.8 ÷ 1.778² = 23.4
- Normalized FFMI = 23.4 + 6.3 × (1.80 − 1.778) = 23.5
Real-Life Examples
- Lifter: 80 kg, 1.80 m and 15% body fat gives an FFMI of 21.0.
- Shorter woman: 62 kg, 1.65 m and 25% body fat gives an FFMI of 17.1 and a normalized FFMI of 18.0.
- Bulking check: gaining 4 kg at the same 15% body fat raises FFMI from 21.0 to 22.0.
- Cutting check: dropping from 80 kg at 15% to 76 kg at 11% keeps FFMI almost the same: 20.9.
FFMI vs BMI
- BMI = weight ÷ height². It is a quick screen but cannot tell muscle from fat.
- FFMI = lean mass ÷ height². It needs a body fat estimate but shows how muscular you are.
- Together: a high BMI with a high FFMI suggests muscle; a high BMI with a normal FFMI suggests extra fat.
FFMI by Height and Lean Mass
Plain FFMI, before height normalization.
| Fat-free mass | 1.65 m | 1.75 m | 1.85 m |
|---|---|---|---|
| 50 kg | 18.4 | 16.3 | 14.6 |
| 55 kg | 20.2 | 18.0 | 16.1 |
| 60 kg | 22.0 | 19.6 | 17.5 |
| 65 kg | 23.9 | 21.2 | 19.0 |
| 70 kg | 25.7 | 22.9 | 20.5 |
| 75 kg | 27.5 | 24.5 | 21.9 |
| 80 kg | 29.4 | 26.1 | 23.4 |
What the FFMI Study Found
Kouri, Pope, Katz and Oliva studied 157 male athletes in 1995: 83 who used anabolic steroids and 74 who did not. The normalized FFMI of the non-users stretched up to a clear limit of 25.0. Twenty Mr. America winners from before steroids were common (1939 to 1959) had an estimated average of 25.4. Many steroid users were well above 25, and some above 30. The authors called these findings preliminary.
The rating bands in the results are a common rough guide for men, not part of the study. Women usually have lower FFMI values, and the bands do not apply to them.
Common Mistakes to Avoid
- Guessing body fat. A 5% error in body fat changes FFMI by about 1 point.
- Entering height in the wrong unit. Use cm in metric and inches in US units.
- Using the men's bands for women. Women usually have lower values.
- Treating 25 as a hard rule. It comes from one 1995 study and was called preliminary.
- Comparing different body fat methods. Use the same method each time you track progress.
Frequently Asked Questions
Fat-free mass index: your lean body mass in kg divided by your height in meters squared.
Find fat-free mass (weight × (1 − body fat %)), then divide by height in meters squared.
For men, about 18 to 20 is average and 22 or more is very muscular. Around 25 was the natural limit in the Kouri study.
FFMI adjusted to a height of 1.80 m by adding 6.3 × (1.80 − your height in meters).
The 1995 study found non-users reached a limit of about 25, but a few people may exceed it, and body fat errors can push numbers up.
Only as accurate as your body fat measurement.
Yes, but typical values are lower and the men's rating bands do not apply.
Lean body mass is a weight in kg or lb. FFMI divides it by height squared so people of different heights can be compared.
That is the correction Kouri and colleagues added to adjust values to a 1.80 m man.
References & Sources
| Source | Used For | Link |
|---|---|---|
| Kouri EM, Pope HG, Katz DL, Oliva P (1995), Fat-free mass index in users and nonusers of anabolic-androgenic steroids | Clin J Sport Med 5(4):223-8. FFMI formula, normalization and the 25.0 limit. | https://pubmed.ncbi.nlm.nih.gov/7496846/ |