Body fat percentage calculator: the US Navy tape method

The US Navy circumference method estimates body fat from height, neck and abdominal or waist measurements, with hip circumference added for the female equation. You need a tape measure, not a photograph.

The result is a rough estimate with a few percentage points of error either way. A reading of 25% means about a quarter of you is fat, not exactly a quarter.

How to measure

Use a flexible tape, keep it level and let it touch the skin without pressing in. Stand normally and measure after a relaxed breath out. Take each measurement twice; if the two disagree, your technique is the variable.

• Height: without shoes, standing upright.
• Neck: just below the larynx, avoiding a tight tape.
• Male equation abdomen: around the abdomen at the navel.
• Female equation waist: the natural waist, at its narrowest practical point.
• Female equation hips: around the widest part of the hips and buttocks.

The form calls the middle measurement “waist,” but the measurement site differs between the two equations: the navel for the male equation, the natural waist for the female one. Measure the wrong place and the estimate moves with it.

The method was developed on military populations, and the National Academies' body-composition review covers its history and limits. This page borrows the equations, not the fitness test.

The calculation behind the result

The calculator uses the circumference-based body-density equations and converts density to an estimated body-fat percentage. All lengths are converted to centimetres first.

For the male equation:

Density = 1.0324 − 0.19077 × log10(abdomen − neck) + 0.15456 × log10(height)

For the female equation:

Density = 1.29579 − 0.35004 × log10(waist + hips − neck) + 0.221 × log10(height)

Then:

Body fat % = 495 ÷ density − 450

You will find published variants that estimate the percentage directly, or use different constants or inches. Feed a centimetre measurement into an inch-based formula and you get a wrong answer, which is why this tool converts everything before it calculates. Published research using the Navy density method

A worked measurement set

Take a man at 180 cm and 80 kg, with 90 cm abdomen and 40 cm neck. The difference between abdomen and neck is 50 cm. Entering those measurements produces a body-fat estimate around 18.4%.

That works out to about 14.7 kg fat mass and 65.3 kg lean mass. Lean mass is everything that is not estimated fat: water, bone and organs as well as muscle, so it is not a muscle number.

If next month's estimate is a little lower, repeat the measurements under the same conditions before you read anything into it. A different tape angle can look like progress.

How accurate is it?

Tape methods are useful for screening and for watching your own trend, but for any one person the error can be several percentage points or more. You will see “about 3–4 points” quoted as a typical error; treat it as a rough size, not a fence around your number.

How well it fits you depends on how much you resemble the original population, where you carry fat, how thick your neck is and how steady your tape hand is. A very muscular neck, for example, shifts the estimate without any real change in total body fat.

When the decision matters clinically or competitively, ask a professional which method fits it. A tape is a tape, not a laboratory assessment.

What to track alongside it

Keep your technique the same each time and write down the actual circumferences, not just the percentage. Then look at the longer weight trend and whether strength, energy and routine are moving the right way.

Our BMI calculator is another screening number with its own blind spots. Neither one tells you what to eat.

If losing fat makes sense for you, the calorie calculator gives you a starting plan and the protein guide helps you build the meals. The form will accept a very low body-fat target; that does not make it a good one.

FAQ

Why is there no result for my measurements?

The equation needs a positive circumference difference and a result in a usable range. Impossible or extreme combinations are rejected rather than shown as zero body fat. Check tape positions and units.

Can I compare this with a smart scale?

They make different assumptions, so a disagreement does not tell you which one is right. Follow one method consistently instead of averaging two unrelated devices.

Does lean mass mean muscle mass?

No. Lean mass includes water, organs, bone and other non-fat tissue. A short-term lean-mass change can reflect hydration.

The easy way to do this

The tape tells you where you are once a month; what moves the number is the record in between. HeyCoach keeps that record in WhatsApp with no app to download: a photo or one line logs a meal, a weigh-in is a number sent in the morning, and a reply fixes any estimate even days later. It remembers your goal, so when you measure again you have a month of evidence beside the new reading. The tape can stay an occasional check.