Body Fat Percentage Calculator

How to use the body fat percentage calculator

This tool estimates your body fat percentage from a few tape measurements using the US Navy circumference method — the same approach a clinic uses when a lab scan is not handy. You enter your height and a couple of girth measurements, and it returns a single percentage alongside the general reference band that figure falls in. The fields start with a representative example (a 175 cm person with a waist of 85 cm and a neck of 38 cm), so you can watch the tool work before you replace them with your own numbers. There is a cm/in toggle if you prefer inches; the math is identical either way.

Accuracy starts with the tape. Use a flexible cloth or vinyl tape, keep it level all the way around, and pull it snug against the skin without compressing it — tight enough not to sag, loose enough not to dent. Measure the waist at the navel, the neck just below the larynx with the tape sloping slightly down to the front, and, if the tool asks for it, the hip at its widest point. Stand relaxed and breathe normally rather than sucking in or puffing out, and take each reading at the same spot every time so day-to-day comparisons stay honest. Two or three readings averaged together beat a single rushed one.

Enter the numbers in the matching fields — height, neck, and waist for everyone, plus hip if the female formula is selected, since that version needs the extra measurement to balance the equation. The calculator subtracts neck from waist (and adds hip for the female formula), takes the logarithm of that girth against your height, and returns the percentage. You do not need to follow the algebra; you just need measurements taken the same careful way each time, because the method is only as good as the tape work feeding it.

Read the percentage next to its band — Essential fat, Athletic, Fitness, Average, or Above average. These are general reference ranges, not goals, grades, or a verdict on your health. Healthy amounts of body fat differ by age, sex, and individual, and a portion of body fat is essential — it cushions organs, stores energy, and supports hormones — so lower is not automatically better and a higher band is not a problem to be fixed. No single number on this page is good or bad; it is just a measurement, the way height or shoe size is.

Treat the figure as one data point and watch the trend, not the decimal. A number that drifts gently over a season tells you far more than a one-off reading, which can swing with hydration, a recent meal, or simply where the tape sat. For a free estimate the tape method is genuinely useful — it typically lands within a few points of a DEXA scan — but calipers and DEXA are more precise, and the tape can read high or low for very muscular or very lean builds. If a number here prompts any health decision, treat it as general information and talk it through with a clinician rather than acting on the estimate alone.

The formula

The US Navy method fits body fat to the ratio between your girth measurements and your height, on a base-10 logarithmic scale. There are two versions because the female formula folds in the hip measurement; both return a percentage directly:

male:   %BF = 495 / (1.0324 − 0.19077·log10(waist − neck) + 0.15456·log10(height)) − 450
female: %BF = 495 / (1.29579 − 0.35004·log10(waist + hip − neck) + 0.22100·log10(height)) − 450

Worked example with the defaults — a 175 cm person with a waist of 85 cm and a neck of 38 cm runs through the male formula to about 16.9%, which falls in the Fitness band. Swap in the female formula with a height of 165 cm, a waist of 75 cm, a neck of 38 cm, and a hip of 95 cm and you get about 24.3%. Change any single measurement and the percentage shifts smoothly, because the whole result rides on the gap between your girths and your height.

This is an estimate, not a diagnosis. The tape method typically lands within a few percentage points of a DEXA scan — remarkable for something that costs nothing — but calipers and DEXA are more precise, and the formula can read high for very muscular builds or low for very lean ones, since it infers fat from girth rather than measuring it directly. The bands the tool shows are neutral reference ranges drawn from general fitness conventions, not targets to hit or grades to earn; healthy ranges vary by age, sex, and person, so use the number to track your own trend rather than to measure yourself against anyone else.

Frequently asked questions

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