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Body fat calculator (US Navy tape method)

Units
Sex
Estimated body fat (US Navy tape method) — BMI-based estimate (Deurenberg formula), for comparison
Body fatCategory
Essential fat
Athletes
Fitness
Average
High
Source: common reference ranges from fitness charts. They are rough guides, not medical standards.
Where to measure
  1. Neck: just below the Adam's apple, tape sloping slightly down towards the front.
  2. Waist (men): level with the navel, stomach relaxed, at the end of a normal breath out.
  3. Hips (women only): around the widest part of the buttocks.

Stand straight with feet together. Keep a flexible tape flat without squeezing the skin. Measure twice and use the average.

Before you read the result

Both methods give estimates with a margin of a few percentage points. A small error at the neck or waist shifts the result.

They do not apply during pregnancy and can be off for very muscular athletes, older adults and teenagers.

This is not medical advice: talk to a doctor to interpret your result.

Unticked, nothing is kept. Ticked, your measurements stay in this browser until you untick it or click "Clear all".

Estimate your body fat with a tape measure

Your weight on the scale does not tell you what it is made of. This body fat calculator estimates the share of fat in your body from three or four tape measurements. It uses the US Navy tape method, a published formula that the Navy has used for decades to assess its personnel, and shows a second estimate based on your BMI alongside it so you can compare the two.

You get your body fat percentage, your fat mass and lean mass in pounds or kilograms, your waist-to-height ratio and a category from five common reference ranges. Everything runs in your browser: no measurement is sent anywhere.

How to use it

  1. Under "Units", keep "Imperial (lb, ft, in)" or switch to "Metric (kg, cm)". Anything you have typed is converted.
  2. Select "Male" or "Female". For women, a "Hips" field appears.
  3. Fill in your height in feet and inches, then "Neck" and "Waist". The percentage appears straight away.
  4. Add "Weight (lb)" to get fat mass and lean mass, then "Age (years)" for the BMI-based estimate.

Nothing is saved by default. If you want to track your numbers from one month to the next, tick "Remember my measurements on this device".

How to take your measurements

The diagram in the tool shows the three spots. Stand up straight with your feet together, wear thin clothing or none, and keep a soft tape flat against the skin without pulling it tight.

  • Neck: just below the Adam's apple, with the tape sloping slightly down at the front.
  • Waist: at the navel for men, at the narrowest point for women, stomach relaxed at the end of a normal breath out.
  • Hips (women): around the widest part of the buttocks.

Measure twice and use the average. Being off by half an inch at the neck or waist moves the result by about one point, so measure at the same time of day each time, for example first thing in the morning.

The formulas

Measurements are converted to centimeters (1 inch = 2.54 cm) and the formulas use base-10 logarithms:

  • Men: 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450
  • Women: 495 ÷ (1.29579 − 0.35004 × log10(waist + hips − neck) + 0.22100 × log10(height)) − 450

The BMI-based estimate uses the Deurenberg formula (1991): 1.2 × BMI + 0.23 × age − 10.8 × sex − 5.4, where sex is 1 for men and 0 for women. It knows nothing about your waist, so treat it as a point of comparison.

Worked example

A 40-year-old man is 5 ft 10 in tall and weighs 170 lb, with a 15-inch neck and a 34-inch waist. His height is 70 in, or 177.8 cm; his neck is 38.1 cm and his waist 86.36 cm. Waist minus neck is 48.26 cm. The denominator comes to 1.0324 − 0.19077 × log10(48.26) + 0.15456 × log10(177.8) = 1.0590, so his body fat is 495 ÷ 1.0590 − 450 = 17.4%. That is 29.6 lb of fat mass and 140.4 lb of lean mass, in the "Fitness" range for men. His waist-to-height ratio is 34 ÷ 70 = 0.49. His BMI is 24.4, and the Deurenberg formula gives 22.3%, about five points higher.

In metric, a woman of 165 cm with a 32 cm neck, 70 cm waist and 95 cm hips gets 24.9%.

Reference ranges

The table in the tool uses the common ranges found in fitness charts: essential fat, athletes, fitness, average and high. The cut-offs differ for men and women, since women naturally carry more essential fat. They are rough guides, not medical standards.

Frequently asked questions

How accurate is this body fat estimate?

It is an estimate with a margin of a few percentage points. It works best for tracking change over time, measured the same way each time, rather than as an exact figure.

Why do the two methods disagree?

The tape method looks at your waist; the BMI formula only knows your weight, height, age and sex. For muscular people, the BMI version often overestimates fat.

Does it work for everyone?

No. It does not apply during pregnancy and can be off for very muscular athletes, older adults and teenagers. It is not medical advice.

Are my measurements stored?

Only if you tick "Remember my measurements on this device". They then stay in your browser, and "Clear all" deletes them.