FFMI Calculator (Fat-Free Mass Index) Free

FFMI (Fat-Free Mass Index) is a body composition metric that estimates muscle mass relative to height. It's calculated as fat-free mass divided by height squared (FFM / height²). Unlike BMI, FFMI accounts for body fat percentage to focus on lean mass.

Normalized FFMI adjusts FFMI for height differences using a common adjustment coefficient (6.1) to compare across heights. The formula adds 6.1 × (1.8m - your height) to your raw FFMI. This makes it easier to compare FFMI values between people of different heights.

The calculator uses the US Navy method, which estimates body fat % from simple measurements: waist, neck, and (for women) hip circumference. This is an estimate based on formulas, not a clinical measurement like DEXA or calipers. The accuracy depends on how accurately you measure these circumferences.

FFMI interpretation depends on many factors including sex, training history, genetics, and body fat %. The calculator shows informational bands (Lower, Average, Above average, High, Very high) based on normalized FFMI. These are general ranges, not medical standards or personal limits.

This calculator does not provide medical advice or make claims about natural limits. FFMI values vary widely based on genetics, training, nutrition, and other factors. The interpretation bands are informational only.

Normalized FFMI adjusts for height differences. Taller people tend to have slightly lower raw FFMI values even with similar muscle mass, so the normalization makes comparisons fairer. The adjustment uses a coefficient of 6.1 and a reference height of 1.8m (about 5'11").

Yes, the calculator works for both men and women. Select your sex to get sex-specific interpretation bands and the correct US Navy formula (women need hip measurement in addition to waist and neck). Female bands are typically shifted slightly lower than male bands, reflecting general differences in body composition.

The calculator's accuracy depends on the accuracy of your measurements (height, weight, waist, neck, hip). The US Navy method is a reasonable estimate for most people, but it's not as accurate as DEXA scans or professional caliper measurements. For best results, measure consistently (same time of day, same conditions) and track trends over time rather than focusing on a single reading.