Body Fat Calculator for Women

How this body fat estimate works

This calculator uses the U.S. Navy circumference method, a formula developed to estimate body fat from a tape measure instead of expensive equipment. For women it needs four numbers: height, neck, waist and hip.

The formula is:

Body fat % = 495 / (1.29579 - 0.35004 x log10(waist + hip - neck) + 0.22100 x log10(height)) - 450

with every measurement in centimetres. The logic behind it is simple: women store fat mostly around the hips and waist, so a larger waist and hip circumference relative to the neck and height means more body fat. The two logarithms stop the relationship from running away at extreme measurements.

It is a solid estimate for most women. Validation studies generally find it lands within 3 to 4 percentage points of a DEXA scan, which is the research-grade method. That is close enough to track change over months, and far better than guessing, but it is an estimate, not a measurement.

If you want a second opinion on your weight category, the CDC's BMI information and the National Heart, Lung, and Blood Institute's overweight and obesity guidance are the standard public references. The World Health Organization fact sheet on obesity covers how these categories are defined internationally.

Worked example: a 5-foot-6 woman

Take a 5-foot-6 woman (167.6 cm) with a 30-inch waist, 40-inch hips and a 12.5-inch neck.

• Convert: waist 76.2 cm, hips 101.6 cm, neck 31.8 cm, height 167.6 cm
• waist + hip - neck = 76.2 + 101.6 - 31.8 = 146.0 cm
• Body fat = 495 / (1.29579 - 0.35004 x 2.1645 + 0.22100 x 2.2244) - 450
• Body fat = 495 / 1.0297 - 450 = 30.7%

On the commonly published ranges, 30.7% sits at the top of the "average" band. If she weighs 150 pounds, that is 46 pounds of fat mass and 104 pounds of lean mass.

Now watch how sensitive the number is. Widen the waist to 32 inches with everything else unchanged and the estimate jumps to 33.2%. Narrow it to 28 inches and it drops to 25.0%. Two inches of waist is worth roughly 2.5 percentage points, which is why consistent measuring technique matters more than the absolute number on any single day.

Worked example: tracking change over 12 weeks

Body fat percentages are most useful as a trend, not a verdict. Suppose the same 5-foot-6 woman starts a walking and strength program and re-measures every four weeks.

Read the last two columns together. She lost 6 pounds of scale weight but gained 4 pounds of lean mass, meaning she lost 10 pounds of fat. That is the single most useful thing a body fat estimate tells you and a bathroom scale never will: whether the weight you are losing is fat or muscle.

Notice too how much the waist drives it: over the 12 weeks she lost 3 inches from her waist and 1.5 inches from her hips, and the estimate fell 5.6 points. Waist measurement dominates this formula, so measure it the same way, at the same time of day, every time.

Reference body fat ranges for women

These ranges are widely published in fitness and clinical literature. They describe populations, not individuals, and they are not a diagnosis.

Two important caveats. First, women carry more essential fat than men for hormonal and reproductive reasons, the same percentage means different things by sex. Second, body fat percentage says nothing about where the fat is. Two women at 30% can have different risk profiles if one carries fat around the abdomen and the other around the hips and thighs. Waist circumference and waist-to-height ratio capture that, which is why clinical guidelines often use them alongside BMI.

How to measure yourself accurately

Bad measurements produce bad estimates, and the tape is where most of the error comes from. Work through this in front of a mirror, ideally with a second person holding the tape level.

• Neck, just below the larynx, tape sloping slightly downward at the front. Do not flex or tuck your chin.
• Waist, at the narrowest point, usually just above the belly button. Stand relaxed and breathe out normally; do not suck in.
• Hips, at the widest point of the buttocks, feet together, tape parallel to the floor.
• Height, barefoot, heels together, back against the wall.

Three rules that improve accuracy more than anything else. Measure first thing in the morning, before eating or drinking. Keep the tape snug but not compressing the skin, a tight tape can cost you an inch and a whole percentage point. And write the numbers down each time so you can see the trend instead of comparing to a memory.

Expect day-to-day noise of about 1 percentage point from hydration and bloating. A change under 2 points over a month is within measurement error; a change of 4 or more points is real.

What body fat percentage does not tell you

A single body fat number is a useful data point and a poor decision-making tool on its own. It does not measure fitness, cardiovascular health, muscle strength, bone density, blood pressure, blood sugar or how well you sleep. A woman at 22% body fat who never exercises and a woman at 30% who lifts four times a week can have different health markers.

It also does not tell you what is healthy for you. Age, genetics, medical history and medications all shift what is realistic and appropriate. Rates of change matter too: losing weight quickly tends to cost lean mass, which is why pairing any fat-loss goal with strength training and adequate protein matters more than the target number.

And the formula has known blind spots. It has no age term, so it cannot account for postmenopausal changes in fat distribution. It is less reliable for pregnant women, for muscular women, and for women at the extremes of the measurement range.

This calculator is a reference estimate, not medical advice. It applies a published formula to the numbers you type in and knows nothing about your health, medications, medical conditions or goals. Use it to track a trend, and talk to a healthcare provider about what a healthy body composition looks like for you specifically.