Body fat percentage — US Navy method with BMI fallback, plus category and guidance.
Waist at the navel (relaxed, not sucked in), neck just below the Adam's apple, hips at the widest point. This is how to measure body fat with a tape — no calipers needed.
Estimates only, for information — not medical advice and not a diagnostic method. Tape-based estimates typically run within a few percentage points of a DEXA scan; calipers, scales and scans all disagree somewhat.
How to use this tool
Pick male or female — the Navy formula is sex-specific (women add a hip measurement).
Enter waist, neck (and hip for women) plus height, in cm or inches. These four numbers drive the body fat percentage result.
Add weight to see fat mass vs lean mass, and age as a fallback if you ever skip the tapes.
Copy your result and re-measure the same way every 2–4 weeks to track the trend.
Formula & worked example
Worked example (man): waist 86 cm (33.86 in), neck 38 cm (14.96 in), height 178 cm (70.08 in). Navy formula: 86.010 × log10(33.86 − 14.96) − 70.041 × log10(70.08) + 36.76 = 86.010 × 1.2765 − 70.041 × 1.8456 + 36.76 ≈ 17.3% — a Fit rating for a man. Woman example: waist 72 cm, neck 32 cm, hip 98 cm, height 165 cm gives ≈ 27.7% (Average for a woman). Fallback example: without tape measurements, a man with BMI 25 at age 30 gets 1.20 × 25 + 0.23 × 30 − 10.8 − 5.4 = 20.7% by the Deurenberg BMI method.
Limitations — read this before you rely on it
Body fat % from a tape is an estimate, not a measurement: expect a few percentage points of error versus DEXA, and small tape-placement differences move the result. It is not a diagnostic tool — it cannot diagnose obesity, eating disorders or any medical condition, and it is not suitable during pregnancy. Very low readings (under essential-fat levels) should not be chased without professional guidance. For health decisions, use the trend and your overall picture (BMI, waist-to-height, blood markers, fitness), not one number alone.
Frequently asked questions
Measure waist at the navel with the tape relaxed (breathe out, do not suck in), neck just below the Adam's apple, and — for women — hips at the widest point around the buttocks. Height in cm or inches. Enter all four and this body fat percentage calculator applies the US Navy formula, which the US military developed from underwater-weighing data.
The Navy method is the best tape-only estimate most people can do at home — typically within about 3–4 percentage points of a DEXA scan. It beats bathroom body fat scales, which swing with hydration. The most accurate methods (DEXA, hydrostatic weighing, Bod Pod) need a lab. For tracking fat loss, what matters most is the trend using the same method every time.
For men: essential 2–5%, athletic 6–13%, fit 14–17%, average 18–24%, obese 25%+. For women: essential 10–13%, athletic 14–20%, fit 21–24%, average 25–31%, obese 32%+. Women carry more essential fat (breasts, hips, reproductive tissue), so healthy ranges run higher — comparing a woman's number to a man's chart is the most common body fat mistake.
If you only know weight and height, the calculator falls back to the Deurenberg BMI method: body fat % ≈ 1.20 × BMI + 0.23 × age − 10.8 (men) or − 0 (women, then − 5.4). It is rougher than the Navy method — muscular people read high — but it gives a usable starting figure. Add tape measurements whenever you can for the better estimate.
Fat mass = weight × body fat %; lean mass is the rest (muscle, bone, water, organs). At 80 kg and 17.3%, fat mass is 13.8 kg and lean mass 66.2 kg. When you lose weight, watch lean mass: if it falls fast, you are likely losing muscle too and should raise protein and keep strength training.