Body Fat Calculator
Use this free body fat calculator to estimate your body fat percentage using the US Navy circumference method. Enter your sex, height, and a few simple tape measurements, and the tool returns your body fat percentage, fat mass, lean mass, and ACE fitness category. Works in both metric and imperial units and runs entirely in your browser, so no data leaves your device.
| Category | Men |
|---|---|
| Essential fat | 2 to 5% |
| Athletes | 6 to 13% |
| Fitness | 14 to 17% |
| Average | 18 to 24% |
| Obese | 25% and above |
The US Navy formula is a circumference-based estimate that is accurate to within about 3 to 4 percentage points compared with DEXA or hydrostatic weighing for most people. Treat the result as a useful indicator rather than a clinical diagnosis. This tool is general information and not medical advice. For body composition decisions tied to health, athletic performance, or weight management, talk to a doctor, a registered dietitian, or a qualified trainer.
Everything you need to estimate body fat
Six features that cover body fat tracking without complexity or signups.
US Navy circumference formula
Uses the equation developed by the US Navy in the 1980s, the most widely used non-scale method for estimating body fat.
Live results as you type
Body fat percentage, lean mass, fat mass, and category update immediately, no Calculate button to press.
ACE fitness categories
See whether you fall into essential, athletes, fitness, average, or obese bands using the American Council on Exercise classification.
Metric and imperial units
Toggle between centimetres and inches without manual conversion. Heights and circumferences flip in place.
100% private, runs in browser
Your measurements stay on your device. Nothing is sent to a server, stored, or shared with anyone.
Mobile-friendly layout
Clean responsive design that works on phones, tablets, and desktops so you can measure anywhere.
Who uses a body fat calculator?
Anyone who wants a clearer picture than the bathroom scale.
Tracking fat loss
Body weight alone hides how much loss is fat versus muscle. Re-measure every few weeks to see if the scale drop is really a fat drop.
Bulking and cutting cycles
Bodybuilders and lifters use body fat to know when to switch between gain and cut phases without relying on weight alone.
Health check-ins
Body fat is a stronger health marker than weight, since two people of the same weight can have very different fat-to-muscle ratios.
Athlete monitoring
Coaches use body fat to track competitive readiness in sports where weight categories or aesthetics matter.
Setting a realistic target
Compare your current body fat with the ACE band you want to be in and work out how many kilograms of fat sit between you and the goal.
Backing up DEXA or scale readings
Use a tape measurement to confirm whether a body fat scale or DEXA result is in the right ballpark, since each method has its own bias.
About body fat percentage
A clear guide to body fat, the US Navy method, and the categories used in fitness.
What is body fat percentage?
Body fat percentage is the proportion of your total body weight that is fat tissue rather than muscle, bone, organs, and water. A 70 kg adult with 20 percent body fat carries 14 kg of fat and 56 kg of lean mass. Body fat is a more meaningful health and fitness marker than total weight because two people of the same weight can have very different proportions of fat to muscle, with very different implications for strength, metabolism, and disease risk.
How the US Navy method works
The US Navy formula was developed in the 1980s to give military medics a quick, equipment-light way to estimate body fat. For men, the formula uses neck and waist circumference along with height. For women, it adds hip circumference. The math behind it is logarithmic: body fat equals 495 divided by (1.0324 minus 0.19077 times log10(waist minus neck) plus 0.15456 times log10(height)) minus 450 for men, with an analogous formula for women that includes the hip measurement.
How to take accurate measurements
Use a soft, non-stretching measuring tape. Stand relaxed without sucking in. Measure the neck just below the larynx with the tape sloping slightly down toward the front. For men, measure waist at the navel. For women, measure waist at the narrowest point and hip at the widest point. Take each measurement twice and average them. Measure at the same time of day, ideally in the morning before eating, since waist can vary by a centimetre or more across the day.
ACE body fat categories
The American Council on Exercise publishes the most common reference bands. For men: essential fat 2 to 5 percent, athletes 6 to 13 percent, fitness 14 to 17 percent, average 18 to 24 percent, obese 25 percent and above. For women: essential fat 10 to 13 percent, athletes 14 to 20 percent, fitness 21 to 24 percent, average 25 to 31 percent, obese 32 percent and above. Women have higher essential fat because of reproductive and hormonal needs.
Essential fat versus storage fat
Essential fat is the minimum your body needs for normal physiological function, including organ padding, nerve sheaths, and hormone production. Storage fat sits in adipose tissue under the skin and around internal organs. Going below essential levels causes serious problems including hormone disruption, loss of menstrual cycles in women, immune suppression, and impaired thermoregulation. Competition bodybuilders sometimes drop to essential levels for a single day, then bounce back.
Body fat versus BMI
BMI uses only height and weight, so it cannot tell muscle from fat. A muscular athlete can have a BMI of 28 and a body fat percentage of 12 percent, while a sedentary person can have the same BMI 28 with 30 percent fat. The two numbers tell very different stories. BMI is still useful as a quick population-level screen, but body fat is the better individual measure of body composition for anyone whose physique sits outside the average range.
Accuracy compared with other methods
Gold-standard methods include DEXA scans, hydrostatic weighing, and air displacement (BodPod), each accurate to about 1 to 2 percentage points but expensive and not widely available. The US Navy method has been validated against these in many studies and is typically accurate to within 3 to 4 percentage points for most people. Bioelectrical impedance scales are convenient but tend to swing 4 to 8 points depending on hydration. The Navy tape method is usually closer to the truth than a home scale.
What body fat percentage should I aim for?
For general health, men do best in the 10 to 20 percent range and women in the 18 to 28 percent range. Athletes pursuing performance often sit lower, but maintenance at very low body fat is hard and not necessary for health. Going extremely lean for short periods may suit a specific competition, but year-round attempts at low single-digit body fat usually backfire. The healthiest target is one you can sustain without obsessive tracking and without compromising training, sleep, and mood.
How often should I re-measure?
Body fat changes slowly. Re-measure every 2 to 4 weeks rather than daily. Daily readings will show noise from hydration, food in the gut, and tape placement that swamps any real change. Track the trend over months, not days. If you are dieting and the scale is dropping but body fat is not, you are likely losing muscle, which is a signal to add protein, lift weights, or moderate the deficit.
Limits of the calculator
The US Navy formula is less accurate at the extremes: very lean individuals and people with very high body fat. It also struggles with body shapes where most fat is stored unusually, such as a slim waist with heavy thigh storage. Pregnancy, certain medications, and severe dehydration can also throw the estimate off. Use the calculator as a guide and a way to track change over time on the same person, not as a tool to compare two different people in absolute terms.
Frequently asked questions
If you don't find your question here, ask us directly.
It uses the US Navy circumference method, which estimates body fat from a few tape measurements: height, neck, and waist for everyone, plus hip for women. The figures are plugged into a published formula based on log base 10, originally derived for the US Navy. It is the most widely used at-home estimate because it needs only a tape measure and gives a number within a few points of more expensive methods.
Use a soft tape, breathe normally, and pull the tape snug without compressing skin. Neck: measure just below the larynx, with the tape level around the neck. Waist: men measure at the navel, women at the narrowest point. Hip (women): measure at the widest point of the buttocks. Take each measurement twice and average. Inconsistent measuring is the single biggest source of error.
For most healthy adults the Navy formula is accurate to within about 3 to 4 percentage points compared to gold-standard methods like DEXA. It is less reliable at the extremes, very lean athletes and people with very high body fat, and it can overestimate for very muscular builds. It is excellent for tracking change over time, even when the absolute number is a few points off.
The American Council on Exercise categories are widely used. For women: essential 10 to 13 percent, athletes 14 to 20, fitness 21 to 24, average and acceptable 25 to 31, obese 32 and above. For men: essential 2 to 5, athletes 6 to 13, fitness 14 to 17, average and acceptable 18 to 24, obese 25 and above. Women carry more essential fat for hormonal and reproductive reasons, so women and men are not directly comparable.
Essential fat is the minimum the body needs for hormones, organ protection, brain function, and reproductive health: about 2 to 5 percent in men and 10 to 13 percent in women. Storage fat is the surplus your body keeps for energy and insulation. Going below the essential level for long periods causes hormone disruption, loss of menstrual cycles in women, and other health problems.
BMI is just weight divided by height squared, so it cannot tell muscle from fat. A muscular athlete and a sedentary person can have identical BMIs but very different body fat percentages and very different health outcomes. Body fat percentage measures what BMI cannot: the share of your weight that is actual fat tissue. Both numbers are useful together.
Once every 2 to 4 weeks is enough. Day-to-day variation from food, water, and bowel content can shift the reading by 1 to 2 percentage points, so a single measurement is noisy. Measure under the same conditions each time: same time of day, before eating, before exercise, with consistent tape technique. The trend across several measurements matters more than any one number.
The Navy formula uses height in a log term to scale the waist and neck measurements relative to body size. Two people with the same waist measurement but different heights have different body proportions and different body fat levels, and the formula accounts for that. Without height the result would be much less accurate.
No, men and women use different formulas because fat distribution differs. Women tend to carry more fat at the hips, so the female formula includes a hip measurement. Men carry more central fat, so the male formula uses only neck and waist. The calculator switches the formula automatically when you select sex.
In order of typical accuracy: DEXA scan, which uses an X-ray scan and is widely considered the clinical reference; hydrostatic underwater weighing; the Bod Pod air-displacement system; skinfold calipers in trained hands; bioelectrical impedance scales; and tape-based methods like this one. DEXA and Bod Pod tests cost money and need a visit. The Navy tape method is the best free at-home option.
Weight is optional. The body fat percentage itself comes from height, neck, waist, and hip and does not need weight. If you add weight, the calculator also shows your fat mass and lean mass in kg or pounds, which is useful when you want to track muscle change rather than just total weight.
No. BMI is a ratio of weight to height and treats all weight equally, so it cannot distinguish muscle from fat. Body fat percentage is the share of total weight that is fat tissue. Two people can have the same BMI but very different body fat percentages, which is why BMI alone is a weak measure of an individual's health.
No. The calculation runs entirely in your browser. Nothing you enter is sent to a server, logged, or shared with anyone. You can use the tool in private and even with the internet disconnected once the page has loaded.
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