Text with personality
Turn plain words into tiny, raised, mirrored and symbol text you can paste anywhere.
Browse fancy textQuick calculators
Percentages, money, grades, math, age, sleep and time tools.
Browse all calculatorsHealth calculators
Calories, macros, body, training, pregnancy and cycle tools.
Browse all calculatorsNumber and code tools
Binary, hex, Roman numerals, Base64, URL encoding and passwords, all in your browser.
Browse all calculatorsEstimate body fat from tape measurements or from height and weight, in US or metric units, with the working shown.
Sources: Military Medicine 2022 (US Marine Corps study) and LibreTexts. Full detail is further down the page.
ACE ranges, left to right: essential fat, athletes, fitness, average, above average.
This is a general estimate for educational use. It is not medical advice, a diagnosis or a treatment plan. Talk to a doctor, registered dietitian or other qualified professional before you change your diet, exercise or health care.
Private by design. Everything runs in your browser and is never uploaded.
A body fat calculator estimates what share of your weight is fat. The U.S. Navy method uses height plus neck and waist measurements, and hip for women. The BMI-based method uses height, weight, age and sex. Both are estimates that can be several percentage points off, so treat the result as a rough guide rather than a measurement.
This body fat calculator runs both methods side by side, turns the percentage into fat mass and lean mass, and shows which American Council on Exercise (ACE) range the number falls in. Results update as you type, the working is written out under the result, and metric and US units give the same answer for the same body. To go further, try the lean body mass calculator or the Army body fat calculator.
| Person | Navy | BMI-based | Fat and lean mass (Navy) |
|---|---|---|---|
| Man, 25, 152 lb, 5 ft 10.5 in, neck 19.5 in, waist 37.5 in | 15.3% | 15.4% | 23.2 lb fat, 128.8 lb lean |
| Woman, 30, 143 lb, 5 ft 5 in, neck 12.5 in, waist 29.5 in, hip 38.5 in | 29.2% | 30.1% | 41.8 lb fat, 101.2 lb lean |
| Man, 40, 85 kg, 180 cm, neck 40 cm, waist 92 cm | 19.9% | 24.5% | 16.9 kg fat, 68.1 kg lean |
| Woman, 45, 70 kg, 168 cm, neck 33 cm, waist 82 cm, hip 102 cm | 33.3% | 34.7% | 23.3 kg fat, 46.7 kg lean |
The first answer is already on screen. Change any number and both estimates update at once, with no Calculate button.
Pick female or male, and US or metric. Switching units converts the numbers you have typed, so nothing needs retyping.
Age, weight, height, neck and waist, plus hip for women. The Navy estimate needs the tape measurements; the BMI-based estimate needs only height, weight and age.
The headline shows the method you choose with its ACE range, fat mass and lean mass. The other method sits underneath so you can compare.
The steps under the result show every number in the formula and the conversions. Copy the result or share a link that opens with the same entries.
The U.S. Navy method is a tape-measure equation published by Hodgdon and Beckett at the Naval Health Research Center in 1984. It takes the log of the difference between waist and neck (waist plus hip minus neck for women) and the log of height, with every length in inches. This calculator converts centimetres to inches first, so a metric entry and a US entry of the same body always give the same number. Some tools use a centimetre and body-density version of the equation, which gives slightly different numbers, sometimes by a point or more.
The BMI-based method is the adult equation from Deurenberg, Weststrate and Seidell (1991), fitted on 1,229 people with a BMI of about 14 to 41 and ages 7 to 83. The authors report an R² of 0.79 and a standard error of 4.1 percentage points. Fat mass is weight times the percentage, and lean mass is what is left. Percentages and masses are rounded to one decimal, half up, for display only. For daily energy use, see the TDEE calculator.
| Value | Formula |
|---|---|
| Navy, men | 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76 |
| Navy, women | 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387 |
| Navy units | Waist, neck, hip and height in inches, log base 10 |
| BMI | Weight in kg ÷ (height in metres)² |
| BMI-based | 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4 (sex: male 1, female 0) |
| Fat mass | Weight × body fat % ÷ 100 |
| Lean mass | Weight − fat mass |
| Conversions | 1 lb = 0.45359237 kg; 1 in = 2.54 cm; feet and inches = (ft × 12 + in) inches |
Where the tape goes changes the answer. These sites follow the descriptions in the US military tape protocol and a university physiology lab guide.
| Measurement | Who | Where the tape goes |
|---|---|---|
| Height | Everyone | Standing, without shoes. |
| Neck | Everyone | Just below the Adam's apple (the laryngeal prominence), with the tape flat against the skin. |
| Waist | Men | Level with the navel (umbilicus). |
| Waist | Women | The narrowest part of the abdomen. |
| Hip | Women only | Around the widest part of the buttocks. |
A study of the tape protocol used lightweight clothing, no shoes and a tape held flat against the skin. Keep the tape level all the way round and take each reading twice. The sources linked below describe the sites but do not set a number of repeats. These waist sites are not the only ones in use: waist-to-height ratio, for example, uses the midpoint between the top of the hip bone and the lowest rib, so use the sites in this table with this calculator.
The American Council on Exercise publishes general ranges for women and men. This calculator only tells you which range a number falls in; it does not label you.
| Range | Women | Men |
|---|---|---|
| Essential fat | 10% to 13% | 2% to 5% |
| Athletes | 14% to 20% | 6% to 13% |
| Fitness | 21% to 24% | 14% to 17% |
| Average | 25% to 31% | 18% to 24% |
| Above the Average range | 32% and over | 25% and over |
ACE describes the Average range as typical for the average non-athlete and names the top band obesity; this calculator calls it the Above the Average range. Each range starts at its lower figure, so 13.5% for a woman falls in the essential fat range. The chart is a general guideline, not a diagnosis, and a body fat percentage does not by itself say anything about a person's health. A result below the lowest range usually means a measurement was off, so measure again.
Every method has an error. This table keeps to what the sources say, in plain words.
| Method | What it needs | What the sources say |
|---|---|---|
| BMI-based formula | Height, weight, age, sex | Standard error of about 4.1 points in the original study. BMI does not distinguish between muscle and fat. |
| U.S. Navy tape method | Height, neck, waist, plus hip for women | In a US Marine Corps study the tape equations averaged 2.5 to 2.6 points below DXA in men and 1.3 to 2.3 points above in women, with a reported spread of 3.7 to 4.8 points. |
| Skinfold calipers | Calipers and a trained person | A trained professional is likely to give a more accurate result than self-measurement. |
| Bioelectrical impedance (BIA) scales | A BIA scale or handheld device | Not as accurate as skinfolds taken by a trained professional. In the Marine Corps study BIA differed from DXA by 1.4 points or less on average. |
| DEXA and hydrostatic weighing | A clinic, lab or imaging centre | Among the most accurate options, but the least accessible and most expensive. Researchers still call DXA an imperfect criterion method. |
Many body fat calculators give one number and a colour-coded label. These are the differences that matter.
| Feature | Typical body fat calculator | This calculator |
|---|---|---|
| Results | Calculate button and a page reload | Updates as you type, with an answer on first load |
| Methods | One method, or two without a reason to pick | Navy and BMI-based side by side, with the gap explained |
| Units | Separate forms for US and metric | One switch that converts what you typed; both give identical results |
| Category wording | Colour-coded labels that can read as a judgement | Neutral ranges from ACE, with the source named |
| Working | Answer only | Each formula with your numbers filled in |
| Error | A single number that looks exact | The published error stated next to the result |
| Sources | Few links, or none | Every formula and range linked to a page that was opened |
| Sharing | Rare | Copy the result or share a link with the same entries |
Enter the same person into this body fat calculator and see how far a tape estimate sits from the figure a bathroom scale reports.
The Navy and BMI-based numbers use different inputs. Putting them next to each other shows how much the answer depends on the method.
Find out which published range a number falls in, without a label attached to it.
A percentage is hard to picture. The fat mass and lean mass lines convert it into the unit you use for weight.
For daily energy and calorie figures see the calorie calculator; for body shape ratios from the same tape measurements see the body type calculator.
Copy the result and the working so a doctor, dietitian or trainer can see exactly which numbers went in.
A body fat percentage is a model, not a reading of your body. These points help you judge how much weight to give it.
The BMI-based formula has a standard error of 4.1 points, and tape equations showed a similar spread against DXA. A true value several points away is normal.
BMI does not distinguish between lean muscle and fat mass, so a muscular person can get a higher estimate than the Navy method gives.
The hip is measured at its widest point, which can include gluteal muscle. Strength training may therefore lead to an overestimate of total body fat.
In a Marine Corps study they overestimated lean people and underestimated people with higher body fat, and were most accurate between 18 and 26 percent for men and 26 and 36 percent for women.
The calculator accepts ages 18 to 100. The BMI formula was fitted on ages 7 to 83 and a BMI of about 14 to 41, and the page warns when you step outside that.
Nothing you type leaves your browser. After the page loads, the calculator keeps working without a connection.
It cannot see inside your body. The BMI-based formula has a published standard error of 4.1 points, and the Military Medicine study of tape equations found a spread of 3.7 to 4.8 points against DXA.
Muscle, body shape and where fat is stored change how well a formula fits. The Human Performance Resource Center notes the limits of circumference methods in women who strength train.
It does not tell you what to weigh, eat or do. DEXA is a reference method for body composition, available through a clinic or imaging centre; ask a doctor or other qualified professional if you want one.
Every formula, range and error figure on this page comes from one of these pages, which were opened while the page was written. The original 1984 Navy reports (Naval Health Research Center reports 84-11 and 84-29) are cited by the Military Medicine paper and the PMC adult-validation paper below, but the report PDFs themselves could not be opened here.
Short answers about the Navy method, the BMI formula and what the numbers mean.
Use the U.S. Navy method: measure height, neck and waist, plus hip for women, then put them into the equation. For men it is 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76, with every length in inches. This calculator does the sums and shows each step.
It is 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387, with all lengths in inches. The waist is measured at the narrowest part of the abdomen and the hip at the widest part of the buttocks.
It is an estimate. In a US Marine Corps study the tape equations averaged 2.5 to 2.6 points below DXA in men and 1.3 to 2.3 points above in women, with a reported spread of 3.7 to 4.8 points. They tended to overestimate very lean people and underestimate people with higher body fat.
It uses the adult equation from Deurenberg and colleagues: 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4, with sex 1 for men and 0 for women. The authors reported a standard error of about 4.1 percentage points, and BMI cannot tell muscle from fat.
They use different inputs: tape measurements for one, and weight, age and sex for the other. Each has a typical error of around 4 points, so a gap of several points is not unusual. Neither is a measurement of your body.
Measure the neck just below the Adam apple, the waist level with the navel for men or at the narrowest part of the abdomen for women, and the hip at the widest part of the buttocks. Keep the tape flat against the skin and level all the way round.
They come from the American Council on Exercise: essential fat, athletes, fitness, average, and a top band that ACE labels obesity. They are general reference ranges, not a diagnosis, and this calculator only shows which range a number falls in.
Essential fat is the amount of fat the body needs for normal function, and below it health can be negatively affected. The ACE chart puts it at 10 to 13 percent for women and 2 to 5 percent for men. A result below these ranges usually points to a measurement error, so measure again.
DEXA is generally used as the reference method for body composition, but researchers call it an imperfect criterion method too. It needs a scanner at a clinic or imaging centre, so ask a doctor or other qualified professional if you want one.
No. These formulas are for adults, so the calculator accepts ages 18 to 100 and shows a note instead of a number below 18. For a child or teenager, ask a doctor or school nurse.
Some tools use a centimetre and body-density version of the equation, and tools may round your measurements differently. A difference of a point or so is small next to the error of the method itself.
No. The calculation runs in your browser and nothing is sent to a server. The numbers appear in the page address only so a shared link opens with the same entries, and your unit choice is remembered on your own device.