The Army uses circumference regression equations developed by Hodgdon and Beckett for the US Navy in 1984. Body fat is estimated from measurable site circumferences and height, requiring only a standard tape measure (no calipers, no water tank). The formula differs by gender because fat distribution patterns differ significantly between sexes.
Worked example (male): 25-year-old, height 5'10" (70 inches), neck 15.5", abdomen 34.5". Abdomen minus neck = 19.0. BF% = 86.010 x log10(19.0) minus 70.041 x log10(70) plus 36.76 = 86.010 x 1.2788 minus 70.041 x 1.8451 plus 36.76 = 110.0 minus 129.2 plus 36.76 = 17.5%. Army standard for ages 21-27 is 22%. This soldier passes with 4.5 percentage points to spare.
The circumference method has a standard error of 3 to 4 percentage points compared to DXA (dual-energy X-ray absorptiometry). It can overestimate fat in muscular soldiers with large abdomens. For body composition metrics beyond Army screening, the FFMI Calculator measures fat-free mass index, which is more useful for tracking lean mass gains.
The 2023 revision of AR 600-9 did not change the circumference formulas or the body fat percentage limits. The Hodgdon-Beckett equations and the age/gender cutoffs have been in place since the original regulation. What the 2023 update changed was the ABCP compliance process and the integration of the Army Combat Fitness Test (ACFT) as the primary physical readiness assessment.
| Component | Pre-2023 | 2023 Revision (Current) |
|---|---|---|
| Measurement formula | Hodgdon-Beckett | Hodgdon-Beckett (unchanged) |
| Body fat limits | Same by age/gender | Same by age/gender (unchanged) |
| ABCP timeline | Up to 12 months | 6 months (extendable to 12) |
| Fitness test | APFT | ACFT (Army Combat Fitness Test) |
| Height-weight screen first | Yes | Yes (unchanged) |
The ACFT replaced the APFT as the primary physical readiness test. Body composition screening remains a separate evaluation from the ACFT score, but both are typically conducted during the same physical readiness testing window. Aerobic capacity is scored directly on the ACFT; the VO2 Max Calculator estimates cardiovascular fitness as a complement to body composition tracking.
AR 600-9 divides soldiers into four age groups: 17-20, 21-27, 28-39, and 40 and above. The allowable limit increases with each group because body fat naturally rises with age, and the Army calibrates standards to remain achievable across a career. Each age group grants 2 additional percentage points for males and 2 for females compared to the group below it.
| Age Group | Male Max BF% | Female Max BF% | Notes |
|---|---|---|---|
| 17-20 | 20% | 30% | Strictest standard; entry-level soldiers |
| 21-27 | 22% | 32% | Core service years; most NCOs in this range |
| 28-39 | 24% | 34% | Mid-career NCOs and company-grade officers |
| 40+ | 26% | 36% | Senior NCOs and field-grade officers |
Age group is determined by the soldier's calendar age on the day of measurement, not the start of the assessment period. A soldier who turns 28 between their last measurement and the next immediately moves to the 28-39 bracket. The Chronological Age Calculator computes exact age in years, months, and days, useful for confirming which bracket applies when a soldier is near a birthday boundary.