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FFMI Calculator
Find your Fat-Free Mass Index (FFMI) in seconds. Enter your weight, height, and body fat percentage, and this calculator works out how much of your body is lean muscle and bone, how that compares with other lifters, and whether your score sits in the average, athletic, or very muscular range.
This calculator is for general information only and is not medical advice. Talk to a doctor or qualified health professional before starting a new diet or training program.
How it works
Body weight alone tells you very little about how muscular someone is. Two people can both weigh 180 pounds, yet one might carry 25 percent body fat while the other carries 12 percent. The second person has far more muscle, and the Fat-Free Mass Index is the number that captures that difference. It measures your lean mass — everything except fat — relative to your height, so it works like a body mass index (BMI) that ignores fat.
The calculation has three steps. First, work out your fat-free mass: take your total weight, convert it to kilograms, and subtract the fat part. If you weigh 180 pounds and your body fat is 15 percent, then 85 percent of your weight is fat-free mass. Second, convert your height to meters and square it. Third, divide your fat-free mass in kilograms by your height in meters squared. That gives your raw FFMI.
There is one more adjustment. Taller people tend to score slightly higher on the raw index and shorter people slightly lower, even at the same level of muscularity, because muscle scales with height in a way the simple division does not fully capture. Researchers therefore adjust the score to a reference height of 1.8 meters (about 5 feet 11 inches). The normalized FFMI adds 6.1 × (1.8 − your height in meters) to the raw value. If you are shorter than 1.8 meters, the adjustment pushes your score up a little; if you are taller, it pulls it down a little. The normalized number is the one to compare against the standard categories.
Here is what the categories mean in practice. Below 18 is below average — typical for someone who does not train. From 18 to 20 is average, where many regular gym-goers sit in their first year. From 20 to 22 is above average, which usually takes a year or two of consistent lifting. From 22 to 24 is athletic, a level that needs several years of serious training and good nutrition. From 24 to 26 is very muscular, the range of competitive natural bodybuilders. Above 26 is rarely reached naturally at all: in research on drug-free lifters, almost nobody scores past 25.
Your result is only as good as your body fat number. A smart scale can be off by several percentage points, which moves your FFMI by roughly half a point either way, so treat the result as a ballpark rather than a precise verdict. A DEXA scan is the most accurate way to measure body fat, and skinfold calipers in trained hands are a good middle ground. Whatever method you use, stick with the same one each time you re-check, so the change in your score over months is meaningful even if the absolute number is slightly off. Track the trend, not a single reading.
Worked example
Alex weighs 180 pounds, stands 70 inches tall, and has a body fat percentage of 15 percent. Here is the full calculation, step by step.
Step 1: Convert weight to kilograms — 180 × 0.453592 = 81.65 kg.
Step 2: Work out fat-free mass — 81.65 × (1 − 0.15) = 81.65 × 0.85 = 69.40 kg.
Step 3: Convert height to meters — 70 × 0.0254 = 1.778 m.
Step 4: Square the height — 1.778² = 3.161.
Step 5: Divide — FFMI = 69.40 ÷ 3.161 = 21.96.
Step 6: Normalize — 21.96 + 6.1 × (1.8 − 1.778) = 21.96 + 6.1 × 0.022 = 21.96 + 0.13 = 22.09.
Alex's FFMI is 21.96 and his normalized FFMI is 22.09, which lands in the athletic range of 22 to 24. That fits a lifter with a few years of consistent training behind him. If Alex dropped to 12 percent body fat at the same weight, his fat-free mass would rise to 71.85 kg and his normalized FFMI to about 22.87 — still athletic, but closer to the very muscular band. Try your own numbers in the calculator above to see where you land.
FAQ
What is a good FFMI?
For most men, an FFMI of 18 to 20 is average, 20 to 22 is above average, and 22 to 24 is athletic. A score of 24 to 26 is very muscular, and scores above 26 are rarely reached without performance-enhancing drugs. For women, the same scale runs roughly 3 to 5 points lower.
What is normalized FFMI and why does it matter?
Normalized FFMI adjusts your raw FFMI to what it would be at a height of 1.8 meters (about 5 feet 11 inches). Taller people naturally score a little higher and shorter people a little lower, so the adjustment lets you compare your score fairly against the standard categories.
How do I measure my body fat percentage for this calculator?
The most practical options are a DEXA scan, which is the most accurate, or skinfold calipers used by a trained person. Smart scales that estimate body fat are convenient but can be off by several percentage points, so treat their number as a rough estimate.
Can women use the FFMI calculator?
Yes. The formula works the same way, but women naturally carry more essential body fat, so the category ranges sit about 3 to 5 points lower. A woman with an FFMI of 17 to 19 is roughly comparable to a man at 20 to 22.
Is an FFMI over 26 possible naturally?
It is extremely rare. In published research on drug-free lifters, almost nobody scores above 25, and scores above 26 are considered a strong sign of performance-enhancing drug use. Genetics, training age, and diet all matter, but 26 is a realistic natural ceiling for most people.