Body Fat Calculator
Estimate your body fat percentage with the U.S. Navy tape-measure method. Enter your height, neck and waist (and hips for women) to see your estimate, category, fat mass and lean mass.
How to Use
- Choose the sex and units: The Navy formula is different for men and women, and women add a hip measurement. Pick metric (cm) or imperial (inches) with the toggle.
- Measure with a flexible tape on bare skin or thin clothing, keeping the tape level and snug but not squeezing:
- Height: standing, without shoes.
- Neck: just below the larynx (Adam's apple), looking straight ahead.
- Waist: for men, level with the navel; for women, at the narrowest part of the natural waist. Breathe out normally and do not pull your stomach in.
- Hips (women): around the widest part of the buttocks.
- Enter the numbers: The result updates as you type, so there is no calculate button.
- Add your weight (optional): This splits your body weight into fat mass and lean mass.
- Repeat under the same conditions: Same time of day, same posture, same tape position. Compare trends over weeks rather than single readings.
What You'll Discover
- Estimated body fat percentage: the share of your body weight the Navy equation predicts is fat, shown to one decimal place.
- Category: where the estimate falls in the Essential Fat, Athletes, Fitness, Average and Obese ranges for your sex (the ranges are in the table below). These are fitness labels, not a medical diagnosis.
- Fat mass: your weight multiplied by the body fat percentage, in kg or lb to match your unit choice. It appears once you enter a weight.
- Lean mass: everything that is not fat (muscle, bone, water and organs), which is your weight minus fat mass.
The calculator shows no result when an entry is missing, when the waist is not larger than the neck (men), or when the estimate falls outside 0–70%, which almost always means a measurement was entered wrongly. This page is general information, not medical advice. For health decisions, talk to a doctor or other qualified clinician.
How the Navy Body Fat Formula Works
This calculator uses the U.S. Navy circumference method, which estimates body fat from tape-measure readings instead of calipers or scans. The equations were developed by Hodgdon and Beckett at the Naval Health Research Center in 1984 (see the men's report and the women's report). The calculator first converts every entry to centimetres, then applies:
Men: BF% = 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450
Women: BF% = 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450
The formula uses sex, height, neck, waist and (for women) hips. It does not use age or body weight; weight is only used afterwards to split your weight into fat mass and lean mass.
Worked example: a man
Height 175 cm, neck 38 cm, waist 85 cm. The waist minus neck is 47, and log10(47) ≈ 1.6721 while log10(175) ≈ 2.2430. The bracket becomes 1.0324 − 0.19077 × 1.6721 + 0.15456 × 2.2430 ≈ 1.0601. Then 495 ÷ 1.0601 ≈ 466.94, and 466.94 − 450 gives about 16.9%, which is in the Fitness range for men.
Worked example: a woman
Height 165 cm, neck 32 cm, waist 75 cm, hips 98 cm. Waist + hip − neck is 141, with log10(141) ≈ 2.1492 and log10(165) ≈ 2.2175. The bracket is 1.29579 − 0.35004 × 2.1492 + 0.22100 × 2.2175 ≈ 1.0335, and 495 ÷ 1.0335 − 450 gives about 28.9%, which is in the Average range for women.
Body Fat Percentage Categories
The calculator labels your estimate with the category names and ranges published by the American Council on Exercise (see ACE's body fat guidance). Women's ranges are higher because essential fat is higher for women.
| Category | Men | Women |
|---|---|---|
| Essential Fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Obese | 25%+ | 32%+ |
Because the published ranges use whole numbers, the calculator treats each range as running up to the start of the next one. For a man, 5.5% counts as Essential Fat, 13.9% as Athletes and 24.9% as Average. An estimate below the essential range (under 2% for men, under 10% for women) is shown as “Below essential range”, which usually points to a measuring error. The ranges do not change with age.
Body fat percentage vs BMI
BMI uses only height and weight, so it cannot tell muscle from fat. Body fat percentage estimates how much of your weight is fat, which is why the two can disagree for very muscular people or for people with little muscle. Use our BMI calculator alongside this one for a fuller picture. The categories above are fitness labels and not a diagnosis; a clinician can interpret your results in light of your health history.
How Accurate Is a Tape-Measure Body Fat Estimate?
Treat the result as a ballpark estimate rather than an exact figure. Published studies that compare circumference-based equations with reference methods report errors of several percentage points for individuals:
- In a study of 31 college-age men, circumference-based military equations, including the Navy and Air Force equation, had a total error of 5.2% fat against a three-compartment reference model. The authors rated that as unacceptable error, while hydrostatic weighing scored 2.5% (Moon et al., 2008).
- In a study of 430 male and 179 female U.S. Marines, an abdominal-circumference-based estimate (related to, but not identical to, this formula) averaged about 2.5 points below DXA for men and roughly 1 to 2 points above DXA for women, with individual spread of roughly 4 to 5 points. Lean people tended to be overestimated and people with higher body fat underestimated (Potter et al., 2022).
These studies used specific groups, so they do not predict your own error, but they show why a single reading should not be treated as precise. The method works best for tracking your own trend with consistent technique.
How the methods compare
| Method | What it uses | Practical notes |
|---|---|---|
| Tape measure (this calculator) | Height, neck, waist, hips | Free and quick; result depends on measuring technique. |
| Skinfold calipers | Fat thickness pinched at body sites | Needs calipers and practised technique. |
| Bioelectrical impedance (smart scales) | A small electrical current | Convenient; readings relate to body water, so conditions matter. |
| DEXA scan | Low-dose X-rays | Done at a clinic or lab; often used as the reference method in studies. |
| Hydrostatic or air-displacement | Body density from water or air displacement | Lab-based; also used as reference methods. |
What Is My Body Fat Percentage If...
What is my body fat percentage if I am a 175 cm man with a 38 cm neck and an 85 cm waist?
About 16.9%, which is in the Fitness range for men. The waist minus neck is 47 cm, and the Navy equation gives 16.94%. At 80 kg that is roughly 13.6 kg of fat and 66.4 kg of lean mass.
What is my body fat percentage if I am a 165 cm woman with a 32 cm neck, 75 cm waist and 98 cm hips?
About 28.9%, which is in the Average range for women. The waist + hip − neck is 141 cm. Raising the waist to 76 cm or the hips to 99 cm moves the estimate to about 29.4%.
What is my body fat percentage if I measure in inches (69 in height, 15 in neck, 33.5 in waist)?
About 16.9% for a man. The calculator converts to centimetres (175.3, 38.1 and 85.1 cm) before applying the formula, so imperial and metric entries of the same body give the same answer.
What is my body fat percentage if my waist is 1 cm bigger?
For the 175 cm / 38 cm neck man above, each extra centimetre of waist adds roughly 0.7 to 0.8 percentage points. At 85 cm the estimate is 16.9%, at 86 cm it is 17.7%, and at 90 cm it is 20.7%. This is why consistent tape placement matters so much.
What is my body fat percentage if my neck measures 1 cm thicker?
A thicker neck lowers the estimate, because the formula uses waist minus neck. For the same man, a 39 cm neck gives 16.2% instead of 16.9%. Flexing your neck muscles, or measuring higher or lower than usual, can shift the reading in the same way.
What is my body fat percentage if my waist equals my neck?
For a man, the calculator shows no result, because the waist minus neck would be zero and the logarithm of zero is undefined. A waist equal to or smaller than the neck usually means a measurement was mistyped or taken in the wrong place. Re-measure both and enter them again.
What is my body fat percentage if I weigh 80 kg and the estimate is 16.9%?
Your fat mass is about 13.6 kg and your lean mass about 66.4 kg. Fat mass is 80 × 16.94% ≈ 13.6 kg (using the unrounded estimate), and lean mass is the remaining 66.4 kg. Lean mass includes muscle, bone, water and organs, not only muscle.
What is my target weight if I weigh 80 kg at 20% and want 15%?
About 75.3 kg, which means losing roughly 4.7 kg of fat if your lean mass stays the same. Lean mass is 80 × 0.80 = 64 kg, and target weight is lean mass ÷ (1 − 0.15) = 64 ÷ 0.85 ≈ 75.3 kg. In practice some lean mass may change too, so treat this as a rough guide. Our calorie calculator can help you plan intake.
What is my body fat percentage if my waist reaches 97 cm?
For the same 175 cm man with a 38 cm neck, a 97 cm waist gives about 25.4%, just above the 25% start of the Obese range in the table. At 96 cm it is 24.7%, in the Average range. The table is a fitness label, so use it as a prompt to talk to a clinician rather than as a diagnosis.
What if the result looks impossibly low or high?
The calculator shows “Check measurements” when the estimate is below 0% or above 70%, and “Below essential range” when it is under the essential minimum. For example, a 165 cm woman entering a neck of 34 cm, waist of 33 cm and hips of 98 cm gets about 4.0%, below the 10% essential minimum for women. That almost always means a measurement was entered wrongly.
People Also Search For
How to calculate body fat percentage with a tape measure
Measure height, neck and waist (plus hips for women), convert them to centimetres, and apply the Navy equation. For a woman of 165 cm with a 32 cm neck, 75 cm waist and 98 cm hips: 75 + 98 − 32 = 141, and 495 ÷ 1.0335 − 450 ≈ 28.9%. The worked examples above show each step, and the calculator does the same in one go.
What is a good body fat percentage for men and women
It depends on your goals and health, and there is no single number that is right for everyone. The ACE ranges in the table label 14–17% (men) and 21–24% (women) as Fitness, and 18–24% and 25–31% as Average. Essential fat is the minimum the body needs, not a target. For personal targets, ask a doctor or dietitian.
How to calculate lean body mass and fat mass
Fat mass = body weight × body fat %, and lean mass = body weight − fat mass. A 70 kg person at 20% has 14 kg of fat mass and 56 kg of lean mass. Enter your weight in the calculator to see both without doing the arithmetic.
How much weight do I need to lose to reach a goal body fat percentage
Divide your lean mass by (1 − goal body fat) to get the target weight, then subtract it from your current weight. At 80 kg and 20% with a 15% goal, that is 64 ÷ 0.85 ≈ 75.3 kg, a loss of about 4.7 kg if lean mass is unchanged. Use the weight loss percentage calculator to track progress as a percentage of your starting weight.
How to lower body fat percentage
Lowering body fat generally means sustaining a modest calorie deficit while keeping enough protein and doing resistance training to protect lean mass. Crash diets tend to cost muscle as well as fat. Work out a maintenance level with the calorie calculator, then discuss a plan with a doctor or registered dietitian, especially if you have a health condition.
Body fat percentage chart by age
This calculator uses one set of ranges for adults, regardless of age. Some published charts adjust the ranges by age, and a clinician can tell you which targets make sense for you. The Navy formula itself does not use age.
Frequently Asked Questions
How accurate is this body fat calculator?
It gives an estimate, not a measurement. Studies comparing circumference-based equations with reference methods report errors of several percentage points for individuals, and the error can differ by sex and by how lean a person is. It is most useful for tracking your own trend with consistent technique. A DEXA scan or other clinical method gives a more reliable single reading.
Which formula does the calculator use?
The U.S. Navy circumference equations by Hodgdon and Beckett. For men: 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450. For women: 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450, with all lengths in centimetres.
Where should I measure my neck, waist and hips?
Measure the neck just below the larynx, the waist level with the navel for men or at the narrowest part of the natural waist for women, and the hips at the widest part of the buttocks (women only). Keep the tape level and snug without squeezing, and breathe out normally without pulling your stomach in.
Why do women need a hip measurement?
The women's Navy equation was built with hip circumference as an input, alongside waist, neck and height, while the men's equation uses only waist, neck and height. Enter your hip size when Female is selected, and the hip field is hidden for Male.
Why is no result showing?
The calculator needs height, neck and waist (plus hips for women). It also shows no number, and displays “Check measurements”, if a man's waist is not larger than his neck, if a woman's waist + hip is not larger than her neck, or if the estimate falls outside 0–70%. Re-measure and check that you chose the right units.
What is a healthy body fat percentage?
There is no single healthy number, and this page does not give medical thresholds. The table above shows the American Council on Exercise category ranges, which are fitness labels. Essential fat is the minimum needed for basic function and is not a goal. A doctor can advise what range suits your age, health and goals.
What is the difference between body fat percentage and BMI?
BMI is weight divided by height squared and cannot separate fat from muscle. Body fat percentage estimates how much of your weight is fat. The two can disagree, for example in someone with a lot of muscle or very little. You can compare them with our BMI calculator.
Does it work for muscular people and athletes?
Use it with caution. In a Marine Corps study of a circumference-based estimate, leaner people were overestimated and people with higher body fat were underestimated compared with DXA. Large neck or waist muscles, or unusual fat distribution, can push the estimate away from your true value.
How often should I measure?
There is no fixed rule, but body fat changes slowly, so very frequent readings mostly capture measuring noise. Measure under the same conditions each time (same time of day, same tape position, ideally with someone else holding the tape) and compare the trend over several weeks.
Does the calculator use my age or weight?
No. The Navy equation uses sex, height, neck, waist and (for women) hips. Your weight is only used afterwards to calculate fat mass and lean mass, and age is not used at all.
Can I use it for children, teenagers or during pregnancy?
This calculator is intended for healthy adults. During pregnancy the waist and hip measurements change for reasons that have nothing to do with body fat, so the estimate would not be meaningful. For children and teenagers, or during pregnancy, ask a doctor how to assess healthy weight and growth.
Do metric and imperial entries give the same result?
Yes. Imperial entries are converted to centimetres (1 inch = 2.54 cm) and weight to kilograms before the calculation, and fat mass and lean mass are shown back in pounds. Switching the toggle does not convert numbers you already typed, so re-enter them in the new unit.
What is lean mass?
Lean mass is your body weight minus fat mass. It includes muscle, bone, water and organs, so it is larger than “muscle mass” alone.
Is this medical advice?
No. The calculator provides a general estimate for information and fitness tracking. It does not diagnose any condition. If you are concerned about your weight, body composition or health, speak to a doctor or other qualified clinician.
Is my data stored or sent anywhere?
No. All calculations run in your browser. Nothing you type is sent to a server or saved, and no account is needed.
Last reviewed: November 2026 — formulas and worked examples verified.