Body Fat Calculator

Body fat, overweight, and obesity

Body fat percentage and body mass index measure related but different things. BMI, covered in more depth on this site's BMI calculator, only ever sees weight relative to height, so it labels "overweight" and "obese" purely from that ratio. Body fat percentage instead estimates what fraction of total weight is actually fat tissue, which is the more direct measurement of the thing most people actually mean when they ask whether someone carries excess body fat. The two numbers usually agree in direction for the average adult, and they can disagree sharply for anyone whose build sits away from the population average, most visibly athletes and heavily muscled adults, where a normal or even low body fat percentage can sit alongside a BMI in the overweight or obese range.

Being "overweight" by body fat percentage, rather than by BMI, means carrying a body fat percentage above the "Average" band for your sex on the American Council on Exercise table below. Obesity, in the body fat sense, means a body fat percentage at or beyond that table's top band, 32% and above for women and 25% and above for men, which is a direct composition-based threshold rather than a weight-for-height ratio.

Potential complications of excess body fat

Carrying a body fat percentage well above the "Average" band is associated, at a population level, with a higher likelihood of several health conditions:

• High blood pressure and elevated LDL cholesterol
• Type 2 diabetes and insulin resistance
• Coronary heart disease and stroke
• Fatty liver disease
• Osteoarthritis from extra load on weight-bearing joints
• Sleep apnea and other breathing difficulties during sleep
• Some cancers, including breast, colon, and endometrial cancer

As with BMI, these are population-level associations rather than a certainty for any one person, and where fat is carried on the body (visceral fat around the abdomen versus fat carried elsewhere) affects the risk level as much as the total percentage does. A body fat percentage is a screening signal, not a diagnosis; a healthcare provider can combine it with other measurements for a fuller picture.

Measuring body fat percentage with the body fat calculator: the U.S. Navy method

Most precise body fat measurements, such as DEXA scans, hydrostatic (underwater) weighing, or skinfold calipers, need equipment that most people do not have at home. The U.S. Navy method was developed as a field-friendly alternative: instead of measuring body density or pinching skinfolds at multiple sites, it uses simple circumference measurements, taken with an ordinary flexible tape measure, and plugs them into a formula derived from regression analysis against measured body density. It was designed so a fitness assessor with no lab equipment could still produce a usable estimate during a routine physical readiness test, and that same simplicity is what makes it a good fit for a home calculator. In effect, this page is a navy body fat calculator: every input and constant below is the same U.S. Navy method the military still uses today, which is also why plenty of visitors specifically search for a US navy body fat calculator or a body fat calculator U.S. Navy method rather than a generic one.

The formula takes height and neck circumference for both sexes, waist circumference for men, and waist plus hip circumference for women. It relies on the fact that, across a large sample of people, the relationship between these circumferences and actual measured body fat follows a fairly consistent pattern once height is accounted for. The male formula is:

The female formula adds hip circumference and uses different coefficients:

Worked example, men (SI/metric). Take a man who is 180 cm tall with a 38 cm neck and an 85 cm waist. The waist minus neck gap is 47 cm. Taking log10 of 47 and log10 of 180, then applying the coefficients above, gives a denominator of roughly 1.062. Dividing 495 by that denominator and subtracting 450 comes out to about 16.1%, which falls in the Fitness category. Change any one of those three measurements and the estimate shifts accordingly, which is why measuring at the correct spot on the body matters so much for this method's accuracy.

Worked example, women (SI/metric). Take a woman who is 165 cm tall with a 32 cm neck, a 75 cm waist, and a 95 cm hip. The waist plus hip minus neck figure is 138 cm. Running that through the female formula gives a denominator of roughly 1.037, and 495 divided by that denominator minus 450 comes out to about 27.4%, which falls in the Average category. Notice that the female formula needs one more measurement than the male formula; that extra hip figure is what lets it account for a body shape and fat distribution pattern the male-only formula was never built to fit.

The same formula, in USC (inches) units

The Navy method also has a published USC form that works directly in inches rather than converting to centimetres first:

Men: Body fat % = 86.010 x log10(waist − neck) − 70.041 x log10(height) + 36.76

Women: Body fat % = 163.205 x log10(waist + hip − neck) − 97.684 x log10(height) − 78.387

Worked example (USC). The same 180 cm/38 cm/85 cm man from the metric example above is 70.87 inches tall with a 14.96 inch neck and a 33.46 inch waist. 86.010 x log10(33.46 − 14.96) − 70.041 x log10(70.87) + 36.76 works out to about 16.2%, matching the SI result of 16.1% to within a couple of tenths of a percentage point. That small gap is expected: the USC form uses its own independently-rounded regression constants rather than being an exact algebraic rearrangement of the SI form, so a small difference between the two is normal, not a sign either one is wrong. This calculator itself only ever computes the SI form internally, converting inches to centimetres first, so its own result always matches the metric worked examples exactly.

Fat mass and lean mass formulas

Once a body fat percentage is known, two more figures follow directly from it and total body weight:

Worked example. A person weighing 80 kg at 20% body fat has a fat mass of 80 × 0.20 = 16 kg and a lean mass of 80 × 0.80 = 64 kg. The two always add back up to total body weight, since every kilogram of a person's weight is counted as either fat mass or lean mass with nothing left over. Enter your age and weight on the calculator above to see your own fat mass and lean body mass alongside your body fat percentage.

How to measure each circumference correctly

Because every input feeds directly into a logarithm, a measurement error of even a centimetre or two can visibly move the result. Use a flexible cloth or vinyl tape measure, not a rigid metal one, and keep it snug against the skin without pulling it tight enough to compress the tissue underneath. Take each measurement two or three times and use the average, ideally at the same time of day, since bloating and hydration can shift waist and hip readings slightly.

• Neck. Wrap the tape just below the larynx (the Adam's apple), with the tape sloping slightly downward toward the front of the neck, matching how a collared shirt would sit.
• Waist. Measure at the navel, standing relaxed, not pulling the stomach in or flexing. This is deliberately not the narrowest point of the torso, which is a common mistake that produces an artificially low estimate.
• Hip (women only). Measure around the widest point of the hips and buttocks, standing with feet together.
• Height. Measure standing barefoot against a wall, looking straight ahead, without shoes adding extra centimetres.

Category bands: the ACE body fat table

The result is placed into one of five bands, using the American Council on Exercise classification, which is split by sex because men and women carry different levels of essential fat needed for normal physiological function. The table below effectively doubles as a body fat percentage chart women and men can each read directly, since essential fat needs differ enough between the sexes that a single shared chart would misclassify one sex or the other:

Put in real numbers rather than just band names: 20 body fat sits inside the Athletes range for women (14-20%) but lands in the Average range for men (18-24%); 18 body fat is Athletes for women and Average for men; 15 body fat is Athletes for women and Fitness for men (14-17%); 12 body fat, sometimes phrased as 12 percent body fat, falls in the Essential fat range for women (10-13%) and the Athletes range for men (6-13%); 10 body fat lands in that same Essential range for women and Athletes for men; and 8 body fat sits below the typical 10-13% essential-fat minimum most women need for normal physiological function, while comfortably inside the Athletes range for men. The takeaway is not that any of these numbers is universally "good" or "bad", it is that the same percentage can land in a completely different category depending on sex, which is exactly why this table is split the way it is.

Ideal body fat for age (Jackson & Pollock)

Body fat that is typical or "ideal" for someone's age is not a single fixed number: essential fat needs, muscle mass, and typical body composition all shift gradually across adulthood. The Jackson & Pollock reference table below is a widely-used way to see what percentage is broadly typical at a given age, for each sex, and is the same table this calculator's own "ideal body fat for your age" result reads from once you enter your age.

Worked example. A 30-year-old man with an estimated body fat of 16.1% compares against a Jackson & Pollock reference figure of 12.7% for his age band. The gap between those two numbers, converted into kilograms of fat using his own weight, is what this calculator reports as "body fat to lose to reach the ideal-for-age figure", a concrete weight-based target rather than a percentage alone.

The BMI method: a second, independent body fat estimate

Alongside the tape-measure-based Navy method, this calculator also reports a completely independent estimate built from the Deurenberg formula, which uses only BMI, age, and sex, no tape measure at all. It comes in two versions, adult and child, and each has a male and a female form, which is why it is usually presented as four variants:

• Adult male/female (age 16+): Body fat % = 1.20 × BMI + 0.23 × age − 10.8 × genderTerm − 5.4, where genderTerm is 1 for male and 0 for female.
• Child male/female (under 16): Body fat % = 1.51 × BMI − 0.70 × age − 3.6 × genderTerm + 1.4

Worked example. A 30-year-old man with a BMI of 22.9 (the same BMI as the 70 kg, 175 cm example on this site's BMI calculator) scores 1.20 × 22.9 + 0.23 × 30 − 10.8 × 1 − 5.4 = 27.48 + 6.9 − 10.8 − 5.4 = 18.18%, shown as 18.2%. That is a genuinely different number from a Navy-method estimate for a different person with a similar build, because the BMI method starts from an entirely different set of inputs and was fitted against a different reference dataset. Seeing both numbers side by side, rather than just one, is itself informative: a wide gap between them usually means the person's build sits away from what one of the two formulas assumes as typical, most often because of an above-average amount of muscle.

An honest accuracy caveat

It is worth being direct about the limits of this method. Circumference-based estimates can be off by several percentage points compared to DEXA or hydrostatic weighing, because the formula only sees a handful of tape measurements and has no way to tell muscle bulk apart from fat at the measurement site. That matters most for people with an athletic build, an unusually muscular neck or waist, or a body-fat distribution that differs from the general population the formula was built from. A bodybuilder with a thick, muscular waist can be pushed toward a higher estimated category than their actual, lab-measured body fat, simply because the formula reads a larger waist circumference as more fat rather than more muscle mass sitting under the skin in that area.

For most people using it to track a general trend over weeks or months, the method is a useful and free proxy: measure the same way, at the same sites, and a consistent downward or upward trend still tells you something real, even if the absolute number carries a few points of uncertainty. For a precise, one-time clinical number, such as for a medical evaluation or a competitive weigh-in, it is not a substitute for lab-based testing like DEXA or hydrostatic weighing, which measure body composition directly rather than inferring it from the outside.