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Body Fat Calculator (US Navy Method)

Estimate body fat percentage from neck, waist and hip measurements using the US Navy method.

Enter the values to see the result here.

For general information, not medical advice. Talk to a doctor before making health decisions.

Formula

The US Navy equations use the base-10 logarithm of body circumferences and height, all in centimetres.

Men:

%BF=4951.0324−0.19077log⁡10(w−n)+0.15456log⁡10(h)−450\%\text{BF} = \frac{495}{1.0324 - 0.19077\log_{10}(w - n) + 0.15456\log_{10}(h)} - 450

Women:

%BF=4951.29579−0.35004log⁡10(w+p−n)+0.22100log⁡10(h)−450\%\text{BF} = \frac{495}{1.29579 - 0.35004\log_{10}(w + p - n) + 0.22100\log_{10}(h)} - 450

where ww is waist, nn neck, pp hip and hh height. Fat mass is body weight times %BF/100\%\text{BF}/100 and lean mass is the remainder.

Worked example

A man 180 cm tall, neck 38 cm, waist 90 cm, weighing 80 kg.

  • w−n=52w - n = 52, log⁡1052=1.716\log_{10} 52 = 1.716; log⁡10180=2.255\log_{10} 180 = 2.255.
  • Denominator: 1.0324−0.19077×1.716+0.15456×2.255=1.05361.0324 - 0.19077 \times 1.716 + 0.15456 \times 2.255 = 1.0536.
  • 495/1.0536=469.8495 / 1.0536 = 469.8, so body fat is 469.8−450≈19.8%469.8 - 450 \approx 19.8\%.
  • Fat mass: 80×0.198=15.880 \times 0.198 = 15.8 kg; lean mass about 64.2 kg.

A waist of 85 cm instead of 90 would give 16.9%, so a 5 cm change at the waist moves the result by almost 3 points.

Common mistakes

  • Measuring the waist at the narrowest point on a man (the formula expects the navel level).
  • Pulling the tape tight enough to indent the skin, which understates the result.
  • Entering inches in the metric fields. Choose the unit system first.
  • Reading the number as exact. Use it to track trends with the same measuring routine.

Frequently asked questions

How accurate is the US Navy method?

It is a screening estimate, usually within about 3 to 4 percentage points of a DEXA scan for most adults. It is less reliable for very lean, very muscular or very heavy people, and changes of under 1 point are within the noise.

Where exactly should I measure?

Neck just below the larynx, sloping slightly down at the front. Waist at the level of the navel for men; for women, at the narrowest point. Hips at the widest point of the buttocks. Keep the tape snug but not pressing, and breathe out normally.

What is a healthy body fat percentage?

ACE ranges for men are roughly 14 to 17% for fit and 18 to 24% for average; for women 21 to 24% for fit and 25 to 31% for average. Essential fat is about 2 to 5% for men and 10 to 13% for women.

Why do women need a hip measurement?

Women typically store more fat around the hips. The female equation adds the hip circumference to correct for that; the male equation does not use it.

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