📏 Body Fat Percentage Calculator
By ToolNimba Health Team · Reviewed by ToolNimba Editorial Review, health and fitness content · Updated 2026-06-19
This calculator gives an estimate only, not a medical measurement. The US Navy method is based on circumference measurements and can be off by several percentage points for any one person, especially if your build differs from the population it was modelled on. It is not a diagnosis and is not a substitute for advice from a doctor or a clinical body composition test. Speak to a qualified health professional before making decisions about your weight or health.
This body fat calculator estimates your body fat percentage using the US Navy circumference method. Choose your sex, pick metric or imperial units, then enter your height, neck and waist (women also add the hip measurement). You get an instant body fat percentage and a category label, with no scales, calipers or special equipment needed beyond a tape measure.
What is the Body Fat Calculator?
Body fat percentage is the share of your total body weight that is fat, with the rest being lean mass such as muscle, bone, organs and water. It is a more useful picture of body composition than weight or BMI alone, because two people of the same weight can carry very different amounts of fat and muscle. The US Navy method estimates this percentage from a handful of tape-measure readings rather than from weight, which is why it works for tracking change over time.
The method relies on circumference measurements because fat tends to gather in predictable places. For men the key inputs are neck and waist: a waist that is large relative to the neck signals more abdominal fat. For women the hip measurement is added, since fat distribution differs. Those circumferences, together with your height, are fed into a logarithmic formula developed by the Naval Health Research Center, which was fitted to match results from more precise lab methods.
Like any estimate from circumferences, it has limits. It assumes a typical relationship between waist size and total fat, so it can over- or under-estimate for very muscular people, for those with unusual proportions, or at the extremes of leanness. Its real strength is consistency: if you measure the same spots the same way each time, the trend it shows (going up or down) is reliable even when the absolute number is only a ballpark.
When to use it
- Estimating your body fat percentage at home with only a tape measure, no calipers or scales required.
- Tracking fat loss or gain over a cut or bulk, where the trend matters more than the exact figure.
- Getting a fuller picture of body composition than weight or BMI alone, which cannot tell fat from muscle.
- Comparing yourself against general fitness categories such as athletic, fitness or average ranges.
How to use the Body Fat Calculator
- Select your sex, since men and women use different formulas.
- Choose metric (cm) or imperial (in) for your measurements.
- Enter your height and the circumference of your neck and waist.
- If you selected female, also enter your hip circumference.
- Read off your estimated body fat percentage and category instantly.
Formula & method
Worked examples
A man who is 178 cm tall, with a 38 cm neck and an 86 cm waist.
- waist − neck = 86 − 38 = 48
- log10(48) = 1.681241 and log10(178) = 2.250420
- denominator = 1.0324 − 0.19077 × 1.681241 + 0.15456 × 2.250420 = 1.059495
- 495 ÷ 1.059495 = 467.20
- body fat % = 467.20 − 450 = 17.20
Result: About 17.2% body fat, which falls in the fitness range for men.
A woman who is 165 cm tall, with a 34 cm neck, a 74 cm waist and 96 cm hips.
- waist + hip − neck = 74 + 96 − 34 = 136
- log10(136) = 2.133539 and log10(165) = 2.217484
- denominator = 1.29579 − 0.35004 × 2.133539 + 0.22100 × 2.217484 = 1.039030
- 495 ÷ 1.039030 = 476.41
- body fat % = 476.41 − 450 = 26.41
Result: About 26.4% body fat, which falls in the fitness range for women.
General body fat percentage categories (American Council on Exercise)
| Category | Men | Women |
|---|---|---|
| Essential fat | 2% to 5% | 10% to 13% |
| Athletes | 6% to 13% | 14% to 20% |
| Fitness | 14% to 17% | 21% to 24% |
| Average | 18% to 24% | 25% to 31% |
| Above average | 25% and over | 32% and over |
Where to take each measurement
| Measurement | How to take it |
|---|---|
| Neck | Just below the larynx (Adam’s apple), tape sloping slightly down to the front. |
| Waist (men) | At the navel, relaxed, not sucking in, after a normal breath out. |
| Waist (women) | At the narrowest point of the natural waist. |
| Hip (women) | At the widest point of the hips and buttocks. |
| Height | Standing straight without shoes against a wall. |
Common mistakes to avoid
- Pulling the tape too tight. A tape squeezed into the skin reads smaller than your true circumference and lowers your estimate. Keep it snug but level, just touching the skin without compressing it.
- Measuring the waist in the wrong place. The method expects the waist at the navel for men and the narrowest point for women. Measuring higher or lower, or sucking your stomach in, changes the result. Pick a spot and reuse it every time.
- Treating the number as exact. Circumference methods carry an error of several percentage points for an individual. Use the figure to track change over weeks, not as a precise lab value to defend to one decimal place.
- Forgetting the hip measurement for women. The women’s formula needs neck, waist and hip. Leaving out the hip, or using the men’s formula, gives a meaningless result.
Glossary
- Body fat percentage
- The proportion of your total body weight made up of fat, with the remainder being lean mass.
- Lean body mass
- Everything that is not fat: muscle, bone, organs, connective tissue and body water.
- Circumference method
- Estimating body fat from tape measurements of body parts rather than from weight or calipers.
- Essential fat
- The minimum body fat needed for normal physiological function, lower in men than in women.
- log10
- The base-10 logarithm, the power to which 10 is raised to give a number, used in the Navy formula.
Frequently asked questions
How accurate is the US Navy body fat method?
It is a reasonable estimate, typically within about 3 to 4 percentage points of methods like underwater weighing for most people. It is less reliable for very muscular or very lean individuals, but it is consistent, so it tracks change over time well even when the absolute number is approximate.
What measurements do I need for the body fat calculator?
Everyone needs height, neck and waist. Women also need the hip measurement. Take each with a flexible tape measure, kept snug but not tight, and measure the same spots the same way each time for comparable results.
Why do men and women use different formulas?
Men and women store fat differently, so the relationship between circumferences and total fat differs. The women’s formula adds the hip measurement and uses different coefficients to reflect this, which is why the calculator asks for your sex.
What is a healthy body fat percentage?
General fitness ranges are roughly 14% to 24% for men and 21% to 31% for women, with athletes often lower. Some fat is essential for health. What is right for you depends on age, goals and overall health, so treat the categories as a guide, not a target.
Is body fat percentage better than BMI?
For body composition, yes, because BMI cannot tell fat from muscle, so a muscular person can look overweight by BMI. Body fat percentage estimates fat directly. BMI is still a quick population-level screen and is simpler to calculate.
How often should I measure my body fat?
Every two to four weeks is enough. Body fat changes slowly, and day-to-day measurement noise from hydration, food and tape placement can swamp real change. Measuring at the same time of day under the same conditions makes the trend clearer.
Sources
- Body Composition Assessment (circumference method origin) , Naval Health Research Center
- Percent Body Fat Norms and Calculations , American Council on Exercise (ACE)