Body Fat Percentage Calculator

What a body fat percentage calculator does, and what it cannot do

Body fat percentage is the share of your total weight that is fat, as opposed to muscle, bone, organs and water. It answers the question the bathroom scale cannot: two people of the same height and weight can be built very differently, and the scale reports one identical number for both. This page estimates that share two ways. The default is the Deurenberg formula, published in 1991, which predicts body fat from three things you already know:

body fat % = 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4
(sex: 1 for men, 0 for women)

Age and sex are in the equation because body composition is not the same at every BMI. At the same height and weight, an adult in their fifties usually carries more fat and less muscle than a twenty year old, and women carry more essential fat than men for reproductive and hormonal reasons. The formula was fitted to people whose body fat had been measured by body density, so it returns the typical value for adults with your BMI, age and sex.

That word typical is the whole caveat. This is an estimate, not a measurement: the paper reports a standard error of 4.1 percentage points for adults, so being four points out in either direction is ordinary. It is furthest off for people whose build is unusual for their BMI, such as a trained lifter. Use it to see which broad range you are in and which way the number is moving, not to settle a figure to one decimal place.

The second is the US Navy tape method, which reads your shape instead of your weight. Its equations were fitted by the Naval Health Research Center in 1984, and the Department of Defense printed them as example equations in DoD Instruction 1308.3 in 2002. Every measurement goes in as inches:

men: body fat % = 86.010 × log10(abdomen − neck) − 70.041 × log10(height) + 36.76
women: body fat % = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387

Men measure the abdomen around the navel; women measure the waist at its narrowest and the hips at their widest. The standard error the researchers report is 3.52 percentage points for men and 3.61 for women, so it is an estimate too. What it adds is shape: at the same weight, a slimmer waist reads lower.

Which method to use for which question

• The BMI formula on this page (BMI, age and sex): you want a free ballpark figure today and a trend line over the coming months. No equipment beyond a scale and a tape for your height.
• The US Navy tape method: you want an estimate that reacts to your shape rather than your weight. It measures height plus the circumference of the neck and waist, with the hips added for women, and ignores weight entirely. Switch the method on this page to Navy tape method to use it.
• Skinfold calipers: you have someone who knows how to use them and will pinch the same sites every time. Cheap, sensitive to change, and heavily dependent on the tester.
• A bioimpedance scale or gym body composition machine: you want a number at home several times a week and understand that hydration moves it. Best read as a weekly average.
• A DEXA scan, air displacement or underwater weighing: you want the closest thing to a real measurement for a baseline or a before and after. Costs money and an appointment, so once or twice a year is realistic.
• BMI on its own: population screening and forms that ask for it. It says nothing about composition.

How to get your estimate

1. Pick your units. The calculator opens in feet, inches and pounds; the Metric option switches to centimeters and kilograms and converts what you already typed.
2. Leave the method on BMI formula, enter height, weight and age, then choose male or female. The formula has no third option.
3. Have a tape measure? Switch the method to Navy tape method and enter height, waist and neck, plus hips for women. Weight and age are not needed; add your weight and the result also shows fat mass. If the BMI formula has your weight and age, its figure is shown beside the tape estimate.
4. Read the three figures that appear: the estimated body fat percentage, the category that percentage falls into, and the BMI it was derived from (fat mass, for the tape method).
5. Check the colored bar underneath. It shows where the estimate sits across the whole range for your sex, which matters more than the number when you are close to a boundary.
6. The reference table and your FFMI, an index of how much lean mass you carry for your height, are folded away below; open them when you want them. The tape method adds a panel that works the equation through with your own numbers.

How to track the number over months

A single reading is close to meaningless. A line of readings taken the same way is genuinely useful, and this is where a formula beats a gadget: it has no hydration noise, because it only knows what you typed. Weigh yourself first thing in the morning, after the bathroom and before breakfast, on the same scale. Record the weight once a week, and come back here once a month to recompute.

Know what the line can and cannot see. Age and sex barely move, so month to month the estimate is your weight change expressed as a percentage: at 5 ft 7 in, every 5.3 lb (2.4 kg) you lose lowers it by one point, whatever that weight was made of. Swap four pounds of fat for four pounds of muscle and your weight is unchanged, so this page reports no progress even though your composition improved. Keep a tape measure reading of your waist in the same note, because that number does move when the formula stays still. To plan the calorie side, the TDEE calculator estimates what you burn in a day.

Why every method and chart gives a different number

• The ranges themselves: the categories on this page follow the widely reproduced chart from the American Council on Exercise. Other organizations publish their own bands, and no body fat cutoff carries the official standing that the BMI thresholds do. Treat the labels as commonly used ranges rather than a medical standard. They are also not adjusted for age, while the formula adds 0.23 points for every year, so the same BMI reads higher with each birthday: a 50-year-old woman with a BMI of 21.6 comes out at 32 percent, the start of the obese band.
• Smart scales and handheld devices: these send a small current through the body and infer fat from the resistance. Readings move with hydration, food and alcohol, a foot to foot scale mostly senses the lower body, and each manufacturer applies its own correction. Two scales disagreeing is normal.
• DEXA scans: the closest thing to a reference in routine use, and repeatable on the same machine. Different manufacturers and software versions do not always agree with each other, so compare scans from the same clinic rather than across clinics.
• Calipers: the result depends on the equation chosen, the sites pinched and the hands holding them. Same tester, useful trend. Different tester, different number.

Limits and health notes

This page is general information, not medical advice. It does not diagnose anything and it is not a substitute for an assessment by a doctor, a registered dietitian or another qualified professional. If you are worried about your weight or planning a significant change to how you eat or train, take that conversation to a clinician who can look at your history rather than to a formula that knows four numbers.

The adult formula applies from age 16. The paper gives a separate equation for children aged 15 and younger, which this page does not use, so it calculates nothing below 16. It should not be used during pregnancy or with significant fluid retention either, and it misreads amputees and very muscular bodies, because in each case weight is not tracking fat the way the formula assumes. The paper also notes a slight overestimate in people with obesity.

The tape equations were fitted to adult Navy personnel, so they are not for children, teenagers or pregnancy either. They depend on technique: a tape a centimeter or two off moves the result by a point or two, so measure at the same places with the same tension each time. They are also not the test a sailor takes today. DoD Instruction 1308.03 of 2022 no longer prints an equation, and the Navy’s body composition guide since December 2025 measures height, waist and weight and screens by waist-to-height ratio.

Lower is not automatically better. The lowest band on the chart is called essential fat, and the summary of the chart that ACE carries describes body fat below 14 percent for women or 6 percent for men as possibly dangerously low. If watching this number starts to feel compulsive, or is driving how much you eat, that is worth raising with someone rather than optimizing further.