Body Fat Calculator
Body fat percentage from tape measurements, by the Navy method.
Recent
Formula
How the calculation works
The tape method compares the neck with the waist. The reasoning is that the neck is mostly bone and muscle and changes little, while the waist grows with fat, so the difference between them tracks fat without needing a scale. Women add the hip measurement, because fat sits differently around the two bodies.
The result is a percentage with a margin of a few points. That is fine for a trend and not fine for a single reading: the same person measured twice, a finger's width apart, can differ by two points. Measure at the same spot, at the same time of day, and compare readings rather than judging one.
Common mistakes
- Measuring the waist at the navel instead of at the narrowest point, which adds several centimetres and several points of fat.
- Measuring over clothing, which adds a centimetre to every reading.
- Forgetting the hip measurement for a woman, which the formula requires and will not guess.
When to use it
- Use it once a month, the same way each time, and follow the change rather than the number.
- Do not use one reading to decide anything. And do not use it at all if the tape values are guesses.
Worked example
Male, 170 cm, neck 37 and waist 82: about 18.9% body fat.
Common questions
Why is the formula different for women?
Because women store fat differently around the hips and waist, so the hip measurement is part of it. One formula for both would be wrong for at least one of them.
Is it as accurate as a machine?
No. A tape carries a margin of a few percent and the figure depends on how you stand and measure. But it is very good for a trend: measure the same way once a month, and the change is the real signal.
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