Body Fat Calculator

What It Does

Estimate your body-fat percentage from three tape measurements — neck, waist and, for women, the hip — together with your height. The page returns the U.S. Navy estimate as the headline figure, with the kilograms of fat and lean mass it implies, the category band it falls in and the reference percentage for your age. A BMI-based estimate is shown beside it, labelled as the weaker method, for readers who have no tape to hand.

Real-World Usage

Tape measurements are how body composition is tracked when a DEXA scan is not available: gyms and sports teams measure every four to eight weeks, and coaches care about the trend rather than the single figure. A physiotherapist or dietitian uses the same numbers to see whether weight lost was fat or muscle. For a reader at home the useful habit is identical conditions each time — same time of day, same tape, same person taking the measurement — because a two centimetre difference between two people reading the same waist is worth about one percentage point.

Local Context

The Navy equations are used the world over and no country publishes its own constants, but the tape itself is local. Waist circumference is measured at the navel in the United States and at the narrowest point in much of Europe, and the two positions can differ by several centimetres on the same person. Where you live also decides whether you reach for centimetres or inches, and whether body-fat percentage or the simpler waist-to-height ratio is the number a doctor quotes at a check-up.

Measuring So the Number Means Something

The estimate is only as good as the tape. Measure on bare skin with a flexible tape, keep it level and snug but never compressing the skin, and read it at the end of a normal breath out — pulling the stomach in changes the result by more than the equation’s own error. The neck is measured just below the larynx with the tape sloping slightly downward at the front. The waist is measured at the navel for the men’s equation and at the narrowest point of the torso for the women’s. Take each circumference twice; if the two readings differ by more than a centimetre, take a third and use the median.

How Far Off the Estimate Can Be

The Navy method predicts body fat from circumference, so it inherits the error of the tape on top of the error of the equation: published validation puts it within roughly three to four percentage points of DEXA for most adults, and the spread widens at the extremes. It reads high in very lean, muscular people and slightly low in people whose fat is mostly abdominal. It was fitted on adults, so it does not apply to children, to pregnancy or to anyone who is very unwell, and it cannot see where fat sits, which is what matters most for metabolic risk. Treat the result as a trend to follow, not a measurement.

The Age Reference, and Why It Is Not a Target

The reference percentage beside your result comes from the Jackson & Pollock tables — a 1978–80 United States survey — and it rises with age because lean mass falls as we get older. It is printed because calculator.net and gigacalculator both print it and a reader should be able to see the same number, not because it is a goal. What is typical of a cohort is not necessarily healthy for one person: a trained runner in their fifties who is below the reference for their age is not under-fat, and a sedentary reader who sits exactly on it is not automatically well.

How accurate is the U.S. Navy body-fat method?

For most adults it lands within about three percentage points of a DEXA scan, which is the reference method. It is least accurate at the extremes: very lean athletes are read high, and people with a lot of abdominal fat are read a little low. One measurement also carries the tape error, so a repeat measurement two weeks later says more than a single figure.

Where exactly do I measure my neck and waist?

Neck: just below the larynx, with the tape sloping slightly down at the front, and without tensing the shoulders. Waist for men: at the navel, level all the way round. Waist for women: at the narrowest point of the torso, usually just above the navel. Keep the tape touching the skin but not pressing in, and measure at the end of a normal breath out.

Why do women need a hip measurement and men do not?

The Navy equations were fitted separately for each sex, and the women’s equation includes the hip because fat distribution differs. Men’s equation uses the waist and neck only. That is why the hip field appears when you select female and disappears when you select male — it is not an optional refinement, it is part of the formula.

Why is the BMI-based estimate the weaker method?

BMI divides weight by height squared and knows nothing about what that weight is made of. A muscular person and a sedentary person of the same height and weight get the same BMI, and therefore the same body-fat estimate, even though their body fat can differ by more than ten points. The equation also drifts with age and ethnicity. It is offered because a rough estimate beats no estimate when there is no tape.

What body-fat percentage is healthy?

The American Council on Exercise bands the categories this page prints: for men, 2–5 % essential fat, 6–13 % athletic, 14–17 % fitness, 18–24 % average and 25 % or more obese; for women, 10–13 %, 14–20 %, 21–24 %, 25–31 % and 32 % or more. Women carry more essential fat by physiology. These are population bands, not a diagnosis, and athletic is not automatically the healthiest place to sit.