Calculated
Body Fat Percentage Calculator
Sign up to favourite this calculatorEstimate your body fat percentage from tape measurements using the US Navy circumference method, with an optional fat-mass and lean-mass breakdown when you add your weight.
Estimated body-fat percentage
US Navy circumference estimate
Estimated category
Typical rangeEstimated fat mass
—Estimated lean mass
—| Step | Value |
|---|---|
| Method | US Navy |
| Sex used for the calculation | Male |
| Measurement unit entered | Centimetres |
| Height | 180 cm |
| Neck circumference | 40 cm |
| Abdomen circumference | 92 cm |
| Formula measurement units | Inches |
| Estimated body-fat percentage | 19.9% |
View the formula
Body-fat % = 86.010 × log₁₀(abdomen − neck) − 70.041 × log₁₀(height) + 36.76
Body-fat % = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387
Every dimension is converted to inches before the logarithms are taken. Age and weight are not part of this calculation.
This is an estimate, not a diagnosis. Tape-measure results vary with tape position, posture, breathing and body shape. Measure under similar conditions each time and focus on the change over weeks rather than a single reading. Estimated lean mass includes muscle, water, bone and organs — it is not a measure of muscle mass alone.
Not medical advice. The US Navy circumference method is a rough estimate from body measurements. It is not equivalent to a DEXA scan, hydrostatic weighing, a BodPod or a clinical assessment, and it does not measure health, fitness or appearance. Body-fat categories are broad reference ranges only.
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Assumptions and limits
- An estimate from the numbers you entered, for guidance only. It is not financial, tax or medical advice.
- Calculator version 1, last updated 25 October 2026.
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What this calculator estimates
This tool gives an estimate of body fat percentage using the US Navy circumference method — also called the tape-measure method. It works from your height and a few body measurements. It is an estimate based on body circumferences, not a medical measurement, a diagnosis, or a direct measure of health, fitness or appearance.
If you add your current weight, it also estimates your fat mass and lean mass. Weight does not change the percentage itself.
How to use this calculator
- Choose the sex to use for the calculation — the formula and fields differ.
- Pick your measurement unit: centimetres or inches. It applies to every measurement.
- Enter your age. The calculator is for adults aged 18 to 120.
- Enter your height and neck circumference.
- For men, enter the abdomen circumference at navel level. For women, enter the natural waist and the hip circumference.
- Optionally add your current weight to also estimate fat mass and lean mass.
- Read your estimated body fat percentage, its reference category, and the breakdown.
Switching the measurement unit converts the values you have already entered.
What do I need to enter?
- Sex used for the calculation — Male or Female. It picks the equation and which circumference fields appear.
- Measurement unit — centimetres or inches, applied to every circumference and to height.
- Age — whole years, from 18 to 120. It confirms the tool applies to you and does not change the percentage.
- Height — 120 cm to 250 cm (about 47.2 to 98.4 in).
- Neck circumference — 20 cm to 65 cm (about 7.9 to 25.6 in).
- Abdomen circumference (men) — 40 cm to 220 cm (about 15.7 to 86.6 in).
- Natural waist circumference and Hip circumference (women) — waist 40 cm to 220 cm, hip 50 cm to 240 cm (about 15.7 to 86.6 in and 19.7 to 94.5 in).
- Current weight (optional) — 30 kg to 350 kg, in kilograms, pounds, or stones and pounds. Leave it blank to skip fat and lean mass.
What do the results show?
- Estimated body-fat percentage — the main figure, to one decimal place. Estimates below 2% or above 70% are withheld and you are asked to re-check your measurements.
- Estimated category — where the percentage falls in the reference categories for your sex.
- Estimated fat mass and Estimated lean mass — your weight split by that percentage. They appear only when you enter a weight.
- How the estimate is worked out — a step-by-step table of the values the formula used.
How the US Navy body fat formula works
Every measurement is first converted to inches, then put through a sex-specific formula that takes the base-10 logarithm of a circumference difference and of height.
Male body-fat % = 86.010 × log₁₀(abdomen − neck) − 70.041 × log₁₀(height) + 36.76
Female body-fat % = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387
- All dimensions are in inches; centimetre input is divided by 2.54 first.
- The abdomen − neck (men) or waist + hip − neck (women) difference must be positive, or the formula has no answer.
- Age and body weight are not used.
Worked example. A man 180 cm tall, neck 40 cm, abdomen 92 cm. In inches that is height 70.87, neck 15.75, abdomen 36.22. Body-fat % = 86.010 × log₁₀(20.47) − 70.041 × log₁₀(70.87) + 36.76 ≈ 112.8 − 129.6 + 36.76 ≈ 19.9%, which falls in the typical reference range.
How to take each measurement
Use a flexible tape measure. Keep it level and snug against the skin without compressing it. Take each measurement twice and average them if the readings differ.
- Height — stand tall, without shoes.
- Neck — measure around the neck just below the larynx, roughly just below the Adam's apple, keeping the tape level rather than sloping.
- Abdomen (men) — measure horizontally around the abdomen at navel level. Stand relaxed and breathe normally; do not pull your stomach in.
- Natural waist (women) — measure around the narrowest part of the torso, usually just above the navel.
- Hips (women) — stand with your feet together and measure around the widest part of the hips and buttocks.
How fat mass and lean mass are estimated
fat mass = body weight × (body-fat % ÷ 100)
lean mass = body weight − fat mass
- Shown only when you enter a weight; otherwise this section is hidden.
- Lean mass here is all non-fat tissue — muscle, water, bone and organs — not muscle mass alone.
What the body fat categories mean
These are broad reference ranges for context only. They are not a diagnosis, a health or appearance assessment, or a target. Body fat percentage alone does not define health or fitness.
| Category | Women | Men |
|---|---|---|
| Essential fat | 10–13% | 2–5% |
| Athlete range | 14–20% | 6–13% |
| Fitness range | 21–24% | 14–17% |
| Typical range | 25–31% | 18–24% |
| Higher range | 32% and above | 25% and above |
Limitations of the tape-measure method
- It is an estimate. Results vary with tape position, tape tension, posture, breathing and body shape.
- It can be several percentage points out for very lean or very muscular people, and for body shapes far from those in the original sample.
- It is not equivalent to a DEXA scan, hydrostatic weighing, a BodPod or a clinical bioelectrical impedance assessment.
- It is for adults. It does not assess health conditions and is not medical advice.
- For a useful comparison, measure under the same conditions each time and watch the trend over weeks rather than a single reading.
To compare this with a height-and-weight screen, use the BMI calculator, or estimate your daily energy needs with the maintenance calories calculator.
Frequently asked questions
What is the US Navy body fat method?
It is a way of estimating body fat percentage from a few tape measurements and your height, developed for the US Navy by the Naval Health Research Center. For men it uses neck and abdomen; for women it uses neck, natural waist and hip. It is a circumference estimate, sometimes called the tape-measure method — not a medical measurement or a body scan.
How is body fat percentage calculated from measurements?
Every measurement is converted to inches, then put through a sex-specific logarithmic formula. For men: 86.010 × log10(abdomen − neck) − 70.041 × log10(height) + 36.76. For women: 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387. Age and body weight are not part of the calculation.
Why does the calculator ask for different measurements for men and women?
The two equations were fitted separately. The male equation is based on the abdominal circumference at navel level; the female equation uses the natural waist and the hip. Entering the wrong measurement for the selected sex gives a misleading result, so the calculator only shows the fields that the chosen formula needs.
How accurate is the tape-measure body fat estimate?
It is a rough estimate. Studies put it within a few percentage points of hydrostatic weighing for many people, but it can be several points out for very lean or very muscular bodies, and small differences in where you place the tape change the result. It is most useful for tracking change over time under consistent conditions, not for a single precise figure.
What is a healthy body fat percentage?
There is no single ideal figure. Broad reference ranges put essential fat at about 2–5% for men and 10–13% for women, with typical ranges higher than that. Body fat percentage on its own does not define health, fitness or appearance, and this calculator does not set a target.
How are fat mass and lean mass worked out?
If you enter your weight, fat mass = weight × (body fat % ÷ 100), and lean mass = weight − fat mass. Lean mass here means everything that is not fat — muscle, water, bone and organs — so it is not a measure of muscle alone. Weight never changes the body fat percentage itself.
Can I use this calculator for a child or teenager?
No. It is designed for adults aged 18 and over. Body composition in children and teenagers changes with growth and should be assessed with age-appropriate guidance from a GP or paediatric professional. The calculator will not produce an estimate for an age under 18.
Last updated 25 October 2026.