Body Fat Calculator
The US Navy tape method, with a BMI-based cross-check and your fat and lean mass.
Descriptive population ranges, not health verdicts. Women carry more essential fat, so the two scales are not comparable.
An estimate for general information, not medical advice. Speak to a doctor or a dietitian before making significant changes.
How to Use
- 1. Choose metric or imperial units and enter your age and sex.
- 2. Enter your height and weight.
- 3. Measure your neck and waist with a tape, plus hips for women.
- 4. Read your estimated body fat percentage, fat mass and lean mass.
What a Tape Measure Can Tell You
The US Navy method works on the difference between girths rather than absolute size. Neck circumference stands in for frame and lean tissue, so subtracting it from the waist isolates the portion of the measurement that actually tracks fat. Women need the hip measurement too, because fat distribution differs enough that a single waist-minus-neck figure would misjudge it.
Accuracy is around 3 to 4 percentage points against a DEXA scan — good enough to follow a trend over months, not precise enough to argue about a single reading. It is least reliable at the extremes and for very muscular builds. What makes it genuinely useful is consistency: same time of day, same tape tension, same landmarks. The direction of travel over eight weeks tells you far more than any one measurement.
The BMI-based estimate is shown alongside as a cross-check because it needs no tape at all, but it only knows your height, weight and age — it cannot distinguish muscle from fat. A lean, muscular person will get a much higher figure from it. When the two disagree sharply, that gap is itself informative, and the tape is the one to trust.
Lean mass is arguably the more useful output. In a deficit, watching lean mass hold steady while fat mass falls is the signal that you are losing the right tissue — something a bathroom scale cannot tell you, since it reports only the total.
Related: BMI Calculator, Calorie Calculator, and Weight Converter.
Frequently Asked Questions
How accurate is the tape measure method?
The US Navy method is typically within about 3 to 4 percentage points of a DEXA scan, which is good enough to track direction over months. It is less accurate at the extremes and for very muscular builds. Measure consistently — same time of day, same tape tension — because the trend matters far more than any single reading.
Why does it ask for my neck?
Because the method works on the difference between girths rather than absolute size. Neck circumference acts as a proxy for frame and lean tissue, so subtracting it from the waist isolates the part of the measurement that tracks fat. Women also need the hip measurement, where fat distribution differs.
What is a healthy body fat percentage?
For men, roughly 14 to 24% covers fitness to average; for women, 21 to 31%. Women carry more essential fat for physiological reasons, so the ranges are not comparable between sexes. Very low percentages are not a health goal — below about 5% for men and 13% for women is the essential fat the body needs to function.
Why do the two estimates differ?
They measure different things. The tape method responds to where your body actually carries fat; the BMI-based estimate only knows your height, weight and age, so it cannot tell muscle from fat. A muscular person will get a much higher figure from the BMI method — when the two disagree sharply, trust the tape.
How should I measure?
Use a flexible tape, snug but not compressing the skin, over bare skin where possible. Waist at the narrowest point for women and at navel height for men; neck just below the larynx; hips at the widest point. Measure first thing in the morning before eating, and take each measurement twice.
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