Navy Body Fat Method: A Tape-Measure Checklist

The U.S. Navy method estimates body fat percentage from a few circumferences: height, neck and waist, plus hips for women. It needs nothing more than a flexible tape, but the result is only as good as your measuring. Measure at the same landmarks, the same time of day and the same tension every time, and the estimate becomes a useful trend line instead of a noisy number.

The result is an estimate for general information, not medical advice.

Why does measuring technique matter so much?

The Navy formula works on the gap between your waist and neck (or waist plus hips minus neck for women), and it takes the logarithm of that gap. Small tape errors change that gap directly, so they show up in the result.

Here is what the Body Fat Calculator returns for a man who is 178 cm tall with a 38 cm neck, weighing 80 kg, when only the waist reading changes:

Waist	Body fat	Category (ACE)	Fat mass
84 cm	15.7 %	Fitness	12.52 kg
86 cm	17.2 %	Fitness	13.76 kg
88 cm	18.7 %	Average	14.96 kg

Four centimeters of tape, easy to gain after a meal or with a tape that slips at the back, moves the estimate by three points and across a category line. The neck works the other way: a 39 cm neck instead of 38 cm drops the 86 cm result from 17.2 % to 16.4 %.

For women the hips join the sum. A woman who is 165 cm tall with a 33 cm neck, 72 cm waist and 98 cm hips gets 26.9 %. With a 74 cm waist reading it becomes 27.9 %.

The before-you-measure checklist

• Pick one time of day. Morning, before eating or a workout, gives the most repeatable readings.
• Use a soft, non-stretch tape. A tailor's tape or a body tape with a lock works best. Metal tape measures don't follow curves.
• Wear little or nothing over the measured areas. Even thin fabric adds millimeters.
• Stand relaxed, feet together. Breathe out normally. Don't hold your breath or pull your stomach in.

The landmark checklist

The calculator's own field labels tell you where to measure:

• Height: barefoot, heels and back touching a wall, eyes looking straight ahead.
• Neck (below the larynx): just under the Adam's apple, with the tape angled slightly downward toward the front.
• Waist: for men, horizontally at the navel; for women, at the narrowest point of the torso.
• Hips (widest point): women only, around the fullest part of the buttocks, tape level all the way round.

Then the technique checks:

• Snug, not tight. The tape should touch the skin all the way around without pressing into it.
• Level. Look in a mirror to make sure the tape isn't dipping at the back.
• Repeat. Take two or three readings at each site and use the average.

How to enter your measurements

1. Open the Body Fat Calculator and set Units to Metric (cm, kg) or Imperial (in, lb).
2. Choose Sex. Selecting Female adds the Hips (widest point) field.
3. Fill in Height, Neck (below the larynx) and Waist. In imperial mode, height goes in as total inches, so 5 ft 10 in is 70.
4. Optionally add Weight (optional) to see Fat mass and Lean mass in the same unit.
5. Read Body fat and Category (ACE). The results update as you type, and the ACE body-fat categories table opens below them.

An imperial example: 70 in tall, 15 in neck, 34 in waist and 176 lb gives 17.4 %, about 30.69 lb of fat mass and 145.3 lb of lean mass. Everything is calculated in your browser, and your measurements are not stored.

What if the calculator shows an error?

• "Please enter all measurements." A required field is empty. For women that includes hips.
• "The waist measurement must be larger than the neck." Usually a typo, or a waist entered in the neck field.
• "These measurements give an implausible result — please check them." The estimate fell outside 0 to 75 %, which nearly always means a mistyped digit.
• No error, but a surprising number. Check that each value is in the unit shown next to its box. Metric and imperial have separate boxes, so switching Units shows a fresh set with inch examples (70 / 15 / 34) instead of reusing your centimetres — type your own measurements into the set you're using. A neck reading in inches typed into a centimetre box, for example, lowers the waist-minus-neck gap and pulls the estimate down.

How should you read the number?

The calculator's note puts the method typically within about 3 to 4 percentage points of a lab measurement, and it is less reliable for very lean or very muscular people. So 17.2 % is best read as "somewhere in the mid-to-high teens." The categories are broad reference bands from the American Council on Exercise, not a judgment about your body, and healthy ranges differ between people. For a second, height-and-weight view, the BMI Calculator is a quick complement.

FAQ

How often should I re-measure?

Every two to four weeks is plenty. Day-to-day changes are mostly measuring noise and water, not fat.

Can I measure over a thin T-shirt?

You can, but the reading will run slightly high and less consistent. If you do, wear the same shirt every time so your trend stays comparable.

Why does a bigger neck lower the estimate?

The formula treats neck size as a rough stand-in for frame and muscle. Subtracting it from the waist (or waist plus hips) narrows the gap that drives the estimate.

Grab a tape and work through the checklist with the Body Fat Calculator.