DEXA Body Composition Interpreter
Interpret DEXA scan results — fat mass index, fat-free mass index, appendicular lean mass index, and visceral adipose tissue — against reference ranges.
📏 Body Composition📐 FMI = fat mass / height²; FFMI = fat-free mass / height²; ALMI = appendicular lean / height²🏥 Health
Sex
Height (cm)
Total mass (kg)
Body fat (%)
Appendicular lean mass (kg, optional)
Visceral adipose tissue (cm² or g, optional)
Please enter valid values.
Formula & Reference
| Variable | Symbol | Formula | Units |
|---|---|---|---|
| DEXA Body Composition Interpreter | — | FMI = fat mass / height²; FFMI = fat-free mass / height²; ALMI = appendicular lean / height² | kg/m² |
Step-by-Step Examples
Example 1
Lean and Muscular
Male, 178 cm, 80 kg, 14% body fat, ALM 29 kg.
- Fat mass = 11.2 kg, fat-free mass = 68.8 kg
- FMI = 11.2 / 3.168 = 3.5 kg/m²
- FFMI = 68.8 / 3.168 = 21.7 kg/m² — above average
- ALMI = 29 / 3.168 = 9.15 — well above the 7.0 cut-point
✓ FFMI 21.7 — above average muscularity
Example 2
Normal Weight, Low Muscle
Female, 165 cm, 60 kg, 32% body fat, ALM 14 kg.
- Fat mass = 19.2 kg, fat-free = 40.8 kg
- FMI = 19.2 / 2.723 = 7.1 kg/m² — lean band
- FFMI = 40.8 / 2.723 = 15.0 — average
- ALMI = 14 / 2.723 = 5.14 — below the 5.5 cut-point
✓ Normal BMI but ALMI below cut-point
Example 3
Elevated Visceral Fat
Male, 175 cm, 88 kg, 26% body fat, VAT 145 cm².
- Fat mass = 22.9 kg, fat-free = 65.1 kg
- FMI = 22.9 / 3.063 = 7.5 kg/m²
- FFMI = 21.3 — above average muscularity
- VAT 145 is well above the ~100 cm² reference
✓ Good muscle mass but elevated visceral fat
Real-World Applications
Beyond Body Fat Percentage
FMI and FFMI separate fat and lean mass relative to height, which a single body fat percentage cannot do.
Sarcopenia Assessment
Appendicular lean mass index is the DEXA measure used in the EWGSOP2 sarcopenia definition.
Visceral Fat
VAT is more strongly associated with cardiometabolic risk than subcutaneous fat, and DEXA estimates it directly.
Tracking Change
Serial DEXA scans distinguish fat loss from lean mass loss in a way scale weight cannot.
Common Mistakes to Avoid
⚠️
Comparing scans from different machines
DEXA results vary between manufacturers and even between software versions. Serial comparisons need the same machine and ideally the same protocol.
⚠️
Scanning under inconsistent conditions
Hydration status, recent meals, and recent exercise all shift results. Morning, fasted, and well-hydrated is the standard for comparability.
⚠️
Treating body fat percentage as precise
DEXA is more accurate than most methods but still carries meaningful error, typically a few percentage points against criterion methods.
Frequently Asked Questions
What is fat-free mass index? ▾
Fat-free mass divided by height in metres squared — a height-adjusted measure of muscularity, analogous to BMI but for lean tissue.
What FFMI indicates high muscularity? ▾
In men, values above about 22 kg/m² indicate well-developed muscularity, with roughly 25 often cited as near the drug-free upper limit. Women's values run several points lower.
What is appendicular lean mass index? ▾
Lean mass of the arms and legs divided by height squared. EWGSOP2 uses cut-points of 7.0 kg/m² for men and 5.5 for women to define low muscle mass.
How accurate is DEXA body fat? ▾
More accurate than bioimpedance or skinfolds but not a perfect criterion method. Errors of a few percentage points against four-compartment models are typical.
How often should I get a DEXA scan? ▾
Every three to six months is common for tracking meaningful change, since shorter intervals often fall within measurement error.