How to Calculate Body Fat Percentage (Navy Method)

Body fat percentage is a more meaningful health metric than BMI because it directly measures the proportion of fat mass in your body. The US Navy formula is one of the most accurate methods that does not require expensive equipment — just a tape measure.

What You Need to Measure

For men: Height, waist circumference (at narrowest point, above navel), neck circumference (below larynx)

For women: Height, waist circumference (at navel), hip circumference (at widest point), neck circumference

Take each measurement 3 times and use the average. Measure at the same time of day (morning is best — before eating or drinking) for consistency.

The US Navy Formula

The equation comes in two forms. They are not interchangeable: each set of constants is fixed to one unit of measurement, so using centimetre measurements in the inch version (or the reverse) gives a result that is wrong by several percentage points.

Metric — all measurements in centimetres:

Men:
Body Fat % = 495 ÷ (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450

Women:
Body Fat % = 495 ÷ (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)) − 450

Imperial — all measurements in inches:

Men:
Body Fat % = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76

Women:
Body Fat % = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387

Both forms describe the same Hodgdon–Beckett equation and agree to within a few tenths of a percentage point when you convert the measurements properly.

Example Calculation (Man, Metric)

Height: 178 cm, Waist: 85 cm, Neck: 38 cm

Body Fat % = 495 ÷ (1.0324 − 0.19077 × log₁₀(85 − 38) + 0.15456 × log₁₀(178)) − 450
= 495 ÷ (1.0324 − 0.19077 × 1.6721 + 0.15456 × 2.2504) − 450
= 495 ÷ (1.0324 − 0.3190 + 0.3478) − 450
= 495 ÷ 1.0612 − 450
= 466.4 − 450
= 16.4% — Fitness category

The same man measured in inches (70.1 in tall, 33.5 in waist, 15.0 in neck) comes out at 16.5% through the imperial form — the same answer, as it should be.

Body Fat Percentage Categories

Category	Men	Women
Essential Fat	2 – 5%	10 – 13%
Athletes	6 – 13%	14 – 20%
Fitness	14 – 17%	21 – 24%
Average	18 – 24%	25 – 31%
Obese	25%+	32%+

Accuracy of the Navy Method

The Navy formula has a margin of error of ±3–4% compared to DEXA (Dual-Energy X-ray Absorptiometry), which is considered the gold standard. This means if your result is 22%, your true body fat is likely between 18–26%.

For better accuracy at home, consistency matters more than the exact number. Measure the same way at the same time and track trends over weeks and months rather than comparing single measurements.

Other Body Fat Methods

• DEXA scan: Gold standard, ±1% accuracy, medical imaging, $50–$150
• Skinfold calipers: ±3–5% with trained technician; inexpensive but technique-dependent
• Bioelectrical impedance (BIA): ±3–5%, varies with hydration level — consumer scales use this
• Hydrostatic weighing: ±1–2%, highly accurate, requires full body submersion
• Bod Pod: ±1–3%, air displacement plethysmography, often found at universities