Body Fat Calculator

What Is Body Fat Percentage?

Body fat percentage is the share of your total weight that is fat, as opposed to everything else — muscle, bone, water, and organs. Two people can weigh exactly the same and stand the same height while carrying very different amounts of fat, which is why the number on the scale alone tells you so little.

It is also the reason body fat percentage is often more useful than BMI. BMI only sees weight and height, so a muscular person can land in the “overweight” band while carrying very little fat. Body fat percentage looks at composition instead, and that is what actually tracks with health risk: too much fat, especially around the middle, raises the risk of heart disease, type 2 diabetes, and several other conditions, while too little fat brings its own problems, from hormone disruption to a weakened immune system.

Our calculator above estimates your body fat percentage from a few tape measurements. It takes less than a minute, needs no lab visit, and nothing is stored or sent anywhere — the math runs entirely in your browser.

How to Take the Measurements

You need a soft tape measure and about two minutes. Measure on bare skin, standing relaxed, and do not pull the tape tight enough to compress the skin. Take each measurement two or three times and use the average — a single sloppy reading is the most common reason for a wrong result.

Neck. Measure just below the Adam’s apple, with the tape sloping slightly downward toward the front. Keep your neck relaxed and do not jut it forward.

Waist. For men, measure horizontally around the navel. For women, measure at the narrowest point of the waist, usually just above the navel. In both cases, breathe out normally and stop — do not suck your stomach in. That one habit alone can move your result by several points.

Hip (women only). Measure around the widest part of the hips and buttocks, keeping the tape level.

Height and weight. Height without shoes, weight on a scale you trust. Weight does not change the percentage itself, but the calculator needs it to split your weight into fat mass and lean mass.

For the most consistent tracking, measure in the morning, before eating, and always at the same spots. Your body fat does not change meaningfully overnight, but your waist measurement can shift during the day with food and water — so same time, same tape, same spots.

The Formula: The US Navy Method

The calculator uses the US Navy circumference method, developed by Hodgdon and Beckett at the Naval Health Research Center in 1984 and validated against underwater weighing. It is the most widely used tape-based formula in the world because it needs no calipers, no scales beyond a bathroom scale, and no lab.

For men, the formula uses height, neck, and waist: Body fat % = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76.

For women, it adds the hip measurement: Body fat % = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387.

All measurements go into the formula in inches — if you enter centimeters, the calculator converts them first, so switching between imperial and metric never changes your result.

The calculator shows the exact formula it used for your numbers, so you can check the arithmetic yourself.

A Worked Example

Take a man who is 70 inches tall (5 feet 10 inches), with a 34-inch waist and a 15-inch neck. First subtract neck from waist: 34 − 15 = 19. Then take the base-10 logarithms: log10(19) is about 1.279, and log10(70) is about 1.845. Plug them in: 86.010 × 1.279 = 110.0, and 70.041 × 1.845 = 129.2. So 110.0 − 129.2 + 36.76 = about 17.5%. That lands in the Fitness range for men.

Now a woman who is 65 inches tall (5 feet 5 inches), with a 29-inch waist, a 38-inch hip, and a 13-inch neck. Waist plus hip minus neck is 29 + 38 − 13 = 54. log10(54) is about 1.732, and log10(65) is about 1.813. So 163.205 × 1.732 = 282.7, and 97.684 × 1.813 = 177.1. Then 282.7 − 177.1 − 78.387 = about 27.3%, which is in the Average range for women.

The Category Table

The American Council on Exercise (ACE) publishes the most widely used adult body fat ranges. They are different for men and women, because women naturally carry more essential fat:

Essential fat: Men 2–5%, Women 10–13%.

Athletes: Men 6–13%, Women 14–20%.

Fitness: Men 14–17%, Women 21–24%.

Average: Men 18–24%, Women 25–31%.

Obese: Men 25% and above, Women 32% and above.

Essential fat is the minimum your body needs to function — below it, health suffers quickly. The athlete range is typical of competitive athletes, not a target most people need. The fitness range is lean and healthy; the average range is where most adults sit. These are population guides, not personal verdicts: age, muscle, and health history all shift what a good number looks like for you.

Common Mistakes

Sucking your stomach in. The single biggest error. A waist measured while holding your breath can read inches smaller and drop your result by several points — and it will not be repeatable tomorrow.

Measuring the waist in the wrong place. Men at the navel, women at the narrowest point. Measuring over clothes, or at the belt line instead, adds noise.

One rushed reading. Tape placement varies by a centimeter or two each time. Average two or three readings and the noise mostly cancels out.

Measuring after a meal. Food and water bloat the waist temporarily. Morning, before eating, is the most repeatable time.

Chasing a single reading. The method is accurate to about ±3–4 percentage points against a DEXA scan, so a one-point move means nothing. Measure weekly under identical conditions and watch the trend over a month — that trend is the truth.

What to Do With Your Number

Alongside the percentage, the calculator shows your fat mass and lean mass — how many pounds or kilograms of you are fat, and how many are everything else. Those two numbers make progress concrete: when you lose weight, you want fat mass to fall while lean mass stays roughly steady, which is why strength training matters during any fat-loss phase.

If your result lands in the average or obese range, the most effective first step is unglamorous: a modest, sustainable calorie gap, daily walking, and two or three strength sessions a week. If it lands in the athlete or essential range without you trying, or if you have a medical condition, are pregnant, or are under 18, treat the result as a rough guide only and talk to a doctor — this formula was validated on adults and is not designed for those cases.

Frequently Asked Questions

1. How accurate is the US Navy body fat method?

For most adults it lands within about ±3–4 percentage points of a DEXA scan, which is the lab reference. That is accurate enough to track change over time, but not precise enough to argue over a single point. Keep your measurement routine identical and read the trend, not one reading.

2. Why do men and women use different formulas?

Men and women store fat differently — women carry more essential fat around the hips and thighs for hormonal and reproductive reasons. The women’s formula adds the hip measurement to account for that, and the category ranges are different for the same reason.

3. What is a healthy body fat percentage?

For most adults, the fitness-to-average range is a reasonable target: roughly 14–24% for men and 21–31% for women, per the ACE ranges above. Essential fat (2–5% men, 10–13% women) is a floor, not a goal — going below it harms health.

4. Why is my result different from my smart scale?

Smart scales use bioelectrical impedance, which swings with hydration, recent meals, and even wet feet — readings can move 4–8% day to day. The tape method is more stable week to week, which is why it is better for tracking, even though neither matches a DEXA scan exactly.

5. Does weight affect my body fat percentage?

Weight does not change the percentage calculation itself — the formula uses only height and circumferences. Weight matters for the second half of the result: fat mass and lean mass, which are your percentage applied to your total weight.

6. How often should I measure?

Once a week, same day, same time (morning, before eating), same tape positions. Daily measurements mostly capture water and food noise, not fat change. Judge progress over four to six weeks, not four to six days.

Try these calculators too: TDEE Calculator, BMI Calculator, Maintenance Calories, Walking Calorie.

Disclaimer: This calculator is for general information only. Body fat estimates are approximations and are not medical advice, diagnosis, or a substitute for professional assessment. If you have a medical condition, are pregnant, are under 18, or have concerns about your weight or body composition, talk to a qualified doctor or registered dietitian.

Sources: Hodgdon & Beckett, Naval Health Research Center (1984), US Navy circumference method; American Council on Exercise (ACE) body fat categories.