Body Fat Percentage Calculator
An estimate from a tape measure that, unlike BMI, can tell muscle from fat, with its real margin of error stated.
In short
The US Navy method estimates body fat from height, neck and waist measurements, plus hips for women. Using a logarithmic formula. It is accurate to roughly ±3–4 percentage points, which is far better than BMI at distinguishing muscle from fat, and far worse than a DEXA scan.
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Measuring properly matters more than the formula
The calculation is only as good as the tape work, and most of the error people see comes from inconsistent measuring rather than the equation.
- Neck: just below the larynx, tape sloping slightly down at the front. Don't flex.
- Waist: at the navel for men; at the narrowest point for women.
- Hips (women): at the widest point, feet together.
- Tape snug, not tight. It should sit on the skin without compressing it.
- Breathe out normally and don't hold it in. Sucking in is the single biggest source of flattering nonsense.
- Measure first thing in the morning, before eating, and repeat under the same conditions each time.
Take each measurement twice. If the two differ by more than half a centimetre, take a third and use the middle value.
Typical ranges
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fit | 14–17% | 21–24% |
| Acceptable | 18–24% | 25–31% |
| Above the healthy range | 25%+ | 32%+ |
Women's ranges are higher throughout, and that is physiology rather than a deficiency, essential fat supports hormone production and reproductive function. Dropping toward the essential minimum carries real consequences, including menstrual disruption and reduced bone density.
Why this beats BMI, and where it doesn't
BMI knows your height and your weight. That's all. It cannot tell a muscular 90 kg from an unfit 90 kg, so athletes are routinely misclassified as overweight.
Circumference measurements track fat far more directly, particularly around the abdomen, which is where the metabolically active fat sits. That's why this method separates two people with identical BMIs.
It still has limits. It assumes a typical fat distribution, so it misreads people who store fat unusually. It has nothing to say about visceral versus subcutaneous fat. And it was developed on military populations, which are not a cross-section of everyone.
How the measurement methods compare
| Method | Typical accuracy | Practical? |
|---|---|---|
| DEXA scan | ±1–2% | Clinic, costly |
| Hydrostatic weighing | ±2% | Lab only |
| Skinfold calipers | ±3–4% skilled, worse otherwise | Needs practice |
| Tape measure (this) | ±3–4% | Free, at home |
| Smart scales (bioimpedance) | ±4–8%, hydration-dependent | Easy, erratic |
| BMI | Not a fat measure at all | Trivial |
Note where bioimpedance scales land. They vary by several points depending on how hydrated you are, which is why the same scale can report a two-point "change" between morning and evening.
Track the trend, not the number
This is the practical advice. The absolute figure carries a few points of uncertainty, but that error is consistent if you measure the same way each time. So a move from 22% to 19% over three months is real information even if the true values were 24% and 21%.
Measure monthly rather than weekly. Body fat changes slowly, and weekly measurement mostly captures measurement noise.
An estimate for personal tracking, not a clinical assessment. Speak to a doctor or registered dietitian before making significant changes, particularly if you have a health condition or any history of disordered eating.
Frequently asked questions
How accurate is the tape-measure method?
The US Navy formula is accurate to roughly ±3–4 percentage points against a DEXA scan. That is considerably better than BMI at telling muscle from fat, and considerably worse than a proper scan. Its real value is consistency: measured the same way each month, the trend is reliable even if the absolute number is a few points off.
Where exactly do I measure?
Neck just below the larynx, tape sloping slightly downward at the front. Waist at the navel for men, at the narrowest point for women. Hips at the widest point. Keep the tape snug but not compressing the skin, breathe out normally, and do not suck in.
What is a healthy body fat percentage?
Broadly 8–19% for men and 21–32% for women, with athletes lower and the essential minimum around 3% and 12% respectively. Women naturally carry more, which is physiological rather than a shortcoming, and going too low carries real health consequences.
Why does it need my height?
Because the formula compares your circumferences to your frame. The same 90 cm waist means something very different on someone 160 cm tall and someone 195 cm tall, and height is what scales the calculation.
Is this better than BMI?
For distinguishing muscle from fat, yes. Clearly. BMI knows only height and weight, so a muscular athlete is classified as overweight. This method uses circumference, which tracks fat far more closely. Neither replaces a clinical assessment.