Body Fat Calculator
Estimate body fat percentage from tape measurements using the US Navy method.
About Body Fat Calculator
The U.S. Navy method estimates body fat from body circumference measurements and height using a validated formula. Measure snugly with a flexible tape for best accuracy.
Formulas
US Navy — Male
BF% = 495 ÷ (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450
- BF%
- Body fat percentage
- w
- Waist circumference (cm)
- n
- Neck circumference (cm)
- h
- Height (cm)
US Navy — Female
BF% = 495 ÷ (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)) − 450
- BF%
- Body fat percentage
- w
- Waist circumference (cm)
- p
- Hip circumference (cm)
- n
- Neck circumference (cm)
- h
- Height (cm)
Worked example
With the default values below, Body Fat Calculator returns Body Fat of 16.9%. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Sexone of Male, Female
- Male
- Height (cm)accepts 100–250 cm
- 175 cm
- Neck (cm)accepts 20–80 cm
- 38 cm
- Waist (cm)accepts 40–200 cm
- 85 cm
- Hip (cm, women only)accepts 40–200 cm
- 95 cm
Results
- Body Fat
- 16.9%
- Category
- Average
Step by step
- 1Circumference difference: waist − neck= 47.00 cm
- 2log₁₀ of (waist − neck)= 1.67210
- 3log₁₀ of height= 2.24304
- 4Compute denominator: 1.0324 − 0.19077 × log(waist−neck) + 0.15456 × log(h)= 1.06010
- 5Body fat % = 495 ÷ denominator − 450= 16.9%
- 6ACE category= Average
Assumptions and limits
- The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 1 decimal place, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
- This is an estimate and not medical advice. Body composition results vary with measurement technique and individual body shape. Consult a healthcare professional for clinical assessment.
- This is an estimate for general information and not professional medical advice. See the full disclaimer for the limits that apply to this kind of calculator.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Body Fat Calculator — full guide
A tape measure beats a bathroom scale
Scale weight cannot tell you whether a 3 kg change was fat, muscle or water. The U.S. Navy circumference method gets at composition with a flexible tape and your height, which is why it spread through military fitness testing and gym intake forms: no calipers, no electrodes, no lab.
The formulas
Measurements go in as centimetres, and the two versions take different circumference sums.
Men:
BF% = 495 ÷ (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450
Women:
BF% = 495 ÷ (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)) − 450
Both work on base-10 logarithms, which is why the result moves fast at small waist-minus-neck values and slowly at large ones.
Worked example
Male, 175 cm tall, 38 cm neck, 85 cm waist:
- Circumference difference:
85 − 38 = 47cm log₁₀(47) = 1.67210log₁₀(175) = 2.24304- Denominator:
1.0324 − 0.19077 × 1.67210 + 0.15456 × 2.24304 = 1.06010 495 ÷ 1.06010 − 450 = 16.9%
Add a 95 cm hip measurement and run the female version on the same height, neck and waist: the sum becomes 85 + 95 − 38 = 142, the denominator 1.03811, and the result 26.8%. The two formulas are not interchangeable — the sexes carry essential fat differently, so each has its own coefficients.
Reading the category
The page labels results on the commonly used American Council on Exercise bands. For men: under 6% essential, 6–13.9% fitness, 14–17.9% average, 18–24.9% above average, 25% and over high. For women each threshold sits higher: under 14% essential, 14–20.9% fitness, 21–24.9% average, 25–31.9% above average, 32% and over high. The 16.9% example lands in average, the 26.8% one in above average.
Technique is most of the error
- Two centimetres of waist changes a lot. Re-run the male example at 87 cm and it reads 18.5% — a 1.5-point jump from tape placement alone.
- Measure at the same time of day, relaxed, after exhaling, tape level and snug without compressing skin.
- Very muscular necks and broad shoulders can push the estimate low; the formula reads a thick neck as leanness.
- Track the trend across weeks rather than reacting to single readings, and treat this as an estimate rather than medical advice — clinical assessment needs DEXA or similar.
Related: BMI for the weight-to-height screen, ideal weight for a target range, and calorie needs to plan the change.
Guides that use this calculator
This is an estimate and not medical advice. Body composition results vary with measurement technique and individual body shape. Consult a healthcare professional for clinical assessment.
Frequently Asked Questions
How accurate is this?
The Navy method is typically within ~3–4% of clinical methods for most people, though technique and body shape affect results. It's a convenient estimate, not a lab measurement.
Where do I measure?
Waist at the navel, neck just below the larynx, and (for women) hips at the widest point. Keep the tape level and snug but not compressing the skin.
Why does the women's version ask for hips when the men's version does not?
The female formula sums waist + hip − neck rather than waist − neck, because hip circumference captures gluteofemoral fat that the waist measurement misses. With a 85 cm waist, 95 cm hip and 38 cm neck the sum is 142 cm. Leave the hip field at a placeholder value and the female result is meaningless.
My waist reads 2 cm larger in the evening than first thing — which do I enter?
Pick one condition and keep it. Morning, before eating, is the most repeatable. That 2 cm is not trivial: on the 175 cm, 38 cm neck example it moves the result from 16.9% to 18.5%, which is enough to cross from the average band into above average without any change in body composition.
What happens if my neck and waist measurements are almost the same?
The male formula takes log₁₀(waist − neck), so as that gap shrinks towards zero the logarithm plunges and the estimate collapses — the page clamps anything negative to 0%. Very lean, thick-necked athletes can break the method this way. If the gap is under about 10 cm, treat the output as unusable.
Should I follow the percentage or the raw tape numbers week to week?
Log both, but trust the tape. Waist, neck and hip are what you actually measured; the percentage is a model built on top of them. A waist falling from 90 cm to 85 cm at a steady weight is solid evidence of recomposition, whatever the derived percentage does.