Skip to the tool
CALCPARK

Body Fat Calculator

Body fat percentage from neck, waist and hip tape measurements with the US Navy method, plus ACE category, fat and lean mass and a BMI-based estimate.

Calculated on your device
Loading the tool…

How to use it

  1. Choose metric or imperial and your sex. Women need an additional hip measurement.
  2. Measure with a flexible tape, snug but not compressing the skin: neck just below the larynx, waist at the navel (men) or the narrowest point (women), hip at the widest point of the buttocks.
  3. Enter the values; the percentage and ACE category update at once. Add your weight for the fat/lean split and your age for the BMI-based estimate.
  4. Repeat under the same conditions (morning, before eating) if you want to track change – the trend is more informative than a single reading.

Example

Man, 175 cm, neck 38 cm, waist 85 cm. Waist minus neck is 47 cm. Body density = 1.0324 − 0.19077 × log₁₀(47) + 0.15456 × log₁₀(175) = 1.0601, and Siri’s equation gives 495 ÷ 1.0601 − 450 = 16.9%. The same man weighing 75 kg carries 75 × 0.169 = 12.7 kg of fat and 62.3 kg of lean mass. At age 35 his BMI is 24.5, so the Deurenberg estimate is 1.20 × 24.5 + 0.23 × 35 − 10.8 − 5.4 = 21.2% – a typical gap between the two methods.

Formulas, categories and limits

US Navy (Hodgdon & Beckett 1984), circumferences and height in cm:
  men:   density = 1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)
  women: density = 1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)
  body fat % = 495 ÷ density − 450   (Siri 1956)

Deurenberg (1991), adults: body fat % = 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4   (sex: men 1, women 0)
Fat mass = weight × body fat %;  lean mass = weight − fat mass

The Navy’s own fitness tables use an equivalent inch-based linear form (men: 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76); it agrees with the density version to within a few tenths of a point. The calculator refuses impossible combinations (a waist no larger than the neck) and clamps the output to 0–70%. Validation studies report a standard error of about 3.5–4% against hydrostatic weighing; errors are larger in very lean athletes and in people with high abdominal fat. The Deurenberg equation was fitted on 1,229 Dutch adults and is a population average, so it should only be read as a cross-check. Categories follow the American Council on Exercise table; “essential fat” is the minimum needed for health, not a goal.

Sources: Hodgdon & Beckett 1984, Naval Health Research Center report 84-11, Deurenberg et al. 1991, Br J Nutr, ACE – What are the guidelines for percentage of body fat loss?.

Both methods are statistical estimates with an error of several percentage points. They are not medical advice and are not suitable for children, pregnant women or people with oedema. Consult a professional before changing your diet or training.

Tape method versus BMI estimate

BMI only knows your height and weight, so the Deurenberg equation must assume an average body composition for your age and sex. The tape method measures where fat is actually stored – the waist – which is why it can tell a muscular 85 kg man from a soft one. If the two numbers differ by more than about 5 points, trust the tape, and if you need a clinical figure, DXA or a calibrated bioimpedance device is the next step.

Questions

Where exactly do I measure the waist?
For the Navy method men measure at the level of the navel and women at the narrowest point of the torso, breathing out normally. Keep the tape level and snug; pulling it tight understates your result.
How accurate is the US Navy body fat calculator?
Studies against underwater weighing give a standard error of roughly 3.5 percentage points, similar to consumer bioimpedance scales. Measuring the same way each time makes the change over weeks far more reliable than the absolute value.
What is a healthy body fat percentage?
On the ACE table the "fitness" and "average" bands are 14–24% for men and 21–31% for women. Essential fat (2–5% men, 10–13% women) is the physiological minimum, not a target.
Why does the tool need my hip only for women?
The Navy equations were fitted separately for each sex; the female equation uses waist plus hip minus neck because women store proportionally more fat around the hips.