Estimate adult body fat percentage, fat mass, and lean body mass using the Hodgdon & Beckett (1984) U.S. Navy circumference method—with Imperial and Metric support.
The U.S. Navy circumference method (Hodgdon & Beckett, 1984) estimates adult body fat percentage from height, neck, and waist circumferences (plus hip circumference for women). In inches, the male equation is BF% = 86.010 × log10(Waist − Neck) − 70.041 × log10(Height) + 36.76, and the female equation is BF% = 163.205 × log10(Waist + Hip − Neck) − 97.684 × log10(Height) − 78.387.
All metric circumference and height inputs (cm) are converted to inches using the exact international definition 1 inch = 2.54 cm so that Imperial and Metric modes yield identical results without coefficient drift. Once BF% is obtained, Fat Mass = Weight × (BF% / 100), Lean Body Mass = Weight − Fat Mass, and estimated Body Density is derived via Siri's (1961) two-compartment relationship Db = 495 / (BF% + 450).
Waist − Neck = 34.0 − 15.5 = 18.5 in. Using Hodgdon & Beckett (1984): BF% = 86.010 × log10(18.5) − 70.041 × log10(70) + 36.76 = 108.99 − 129.23 + 36.76 = 16.5%.
Estimated Body Fat: 16.5% | Fat Mass: 29.7 lb (13.5 kg) | Lean Body Mass: 150.3 lb (68.2 kg) | Body Density: 1.0611 g/cm³.
Waist + Hip − Neck = 28.0 + 38.0 − 13.0 = 53.0 in. Using Hodgdon & Beckett (1984): BF% = 163.205 × log10(53.0) − 97.684 × log10(65) − 78.387 = 281.41 − 177.09 − 78.387 = 25.9%.
Estimated Body Fat: 25.9% | Fat Mass: 36.3 lb (16.5 kg) | Lean Body Mass: 103.7 lb (47.0 kg) | Body Density: 1.0401 g/cm³.
In validation studies by Hodgdon and Beckett (1984) at the Naval Health Research Center, circumference equations showed correlation coefficients of r = 0.85 to 0.90 against hydrostatic (underwater) weighing, with a standard error of estimate (SEE) of roughly ±3.2% to ±3.7% (approximately ±3% to ±4% versus clinical DXA). While less precise than laboratory imaging, it is one of the most reliable non-invasive field methods when measurements are taken consistently at standardized anatomical landmarks.
For both men and women, measure the neck just below the larynx (Adam's apple). For men, measure the waist horizontally across the navel (umbilicus) at the end of a normal exhalation. For women, measure the waist horizontally at the narrowest part of the torso (natural waist) and additionally measure the hips horizontally around the widest part of the buttocks/gluteal region.
This calculator implements the classic multi-site Hodgdon & Beckett (1984) equations (NHRC Reports 84-29 and 84-11), measuring neck and waist (and hips for women). Some modern military service branches (such as DoD 2023 updates) use a single-site abdominal tape screening protocol for body composition pass/fail compliance before secondary assessment.
No. Fitness category tiers (such as American Council on Exercise reference ranges) are descriptive population fitness benchmarks, not clinical diagnostic criteria. Lean mass and fat mass outputs are mathematical model estimates based on the circumference equations, not direct cellular tissue scans.
Adult men and women exhibit different typical patterns of subcutaneous fat distribution (android/abdominal vs. gynoid/gluteofemoral). During NHRC regression modeling (Report 84-11), adding hip circumference significantly reduced prediction error for female service members compared to waist-and-neck alone.
Once you have your estimated body fat percentage and Lean Body Mass (LBM) from this calculator, you can enter your Body Fat % into PeekAndDo's TDEE & Daily Calorie Calculator and select the Katch-McArdle BMR formula, which calculates resting energy expenditure directly from Lean Body Mass.