Body Fat Calculator

This body fat calculator estimates what share of your weight is fat, using the tape-measure method developed for the U.S. Navy. The example loaded on this page, a 25-year-old man at 160 lb and 5 ft 10 with a 36 inch waist and a 16 inch neck, comes out at 19.3% body fat, which is 30.9 lb of fat against 129.1 lb of lean mass and lands in the Average category. It also runs the BMI-based estimate alongside it, which returns 17.1% for the same person, and that two-point gap is a fair illustration of how much any estimate can move depending on the method.

What body fat actually is

The clinical term is adipose tissue, and it does more than sit there. It stores lipids the body converts to energy, secretes hormones including leptin and adiponectin, cushions organs, and insulates you. A body with too little of it does not function well, which is why the goal is a healthy range rather than the lowest number possible.

Fat divides into two kinds. Essential fat is the minimum needed for life and reproductive function, roughly 2% to 5% in men and 10% to 13% in women. Storage fat is everything above that, and it splits again: subcutaneous fat sits under the skin, while visceral fat packs in around the organs inside the abdominal cavity. When research links body fat to disease risk, visceral fat is usually the culprit.

Healthy ranges land near 8% to 19% for men and 21% to 33% for women. Women carry more essential fat for hormonal and reproductive reasons, so comparing a man's number against a woman's is meaningless.

The Navy method, and how to measure properly

The formulas come from work by Hodgdon and Beckett at the Naval Health Research Center in 1984, and they estimate body fat from circumferences alone. In inches:

Men: BFP = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76

Women: BFP = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387

From there, fat mass is body fat percentage times weight, and lean mass is whatever is left. The measurements themselves decide the accuracy, so take them the same way every time:

• Waist: at the navel for men, at the narrowest point for women, tape level all the way round, and do not hold your stomach in.
• Neck: just below the larynx, with the tape sloping slightly downward at the front, and without flaring the neck out.
• Hips (women): at the widest point.

A half-inch error on the waist moves the result by roughly a full percentage point, so measure twice, take the average, and always at the same time of day. First thing in the morning before eating is the most repeatable.

How accurate is any of this

The Navy method typically lands within about 3 to 4 percentage points of a DEXA scan, which is respectable for something that costs nothing and takes two minutes. It is least reliable at the extremes: very lean people and very heavy people both tend to be misestimated, and anyone carrying unusual muscle distribution can throw it off, because the equation infers fat from girth and cannot tell muscle from fat.

The BMI-derived estimate on this page is weaker still, since BMI itself cannot distinguish tissue types. It is shown for comparison rather than as a second opinion. If the two figures disagree by several points, trust the tape.

What matters more than absolute accuracy is consistency. A method that reads two points high every time still tracks change perfectly, and change is what you are actually monitoring. The BMI Calculator covers where that measure works and where it fails.

The other ways to measure

• DEXA: an x-ray scan that separates fat, lean tissue, and bone, and reports where the fat sits. The practical gold standard, roughly $50 to $150 a scan.
• Hydrostatic weighing: underwater weighing based on density. Very accurate, awkward to arrange, and requires fully exhaling underwater.
• Air displacement (Bod Pod): the same density principle using air rather than water, quicker and more comfortable.
• Skinfold calipers: pinching at three or seven sites using the Jackson and Pollock equations. Cheap and decent in trained hands, unreliable in untrained ones.
• Bioelectrical impedance: the method in smart scales and handheld devices. It passes a current through the body and infers composition, which makes it very sensitive to hydration; the same person can read three points apart before and after a glass of water.

Why the waist matters more than the scale

Two people at identical weights can carry completely different health risk depending on where the fat sits, which is why a tape often tells you more than a scale. Visceral fat is metabolically active in ways subcutaneous fat is not: it releases inflammatory signalling proteins, pushes LDL cholesterol up and HDL down, and drives insulin resistance, the process where cells stop responding properly to insulin and blood sugar climbs toward type 2 diabetes.

A useful companion measure is waist-to-height ratio: keep your waist under half your height. At 5 ft 10, that means a waist below 35 inches. It takes one measurement, applies across ages and both sexes, and flags abdominal fat that BMI misses entirely.

What excess body fat does

Obesity is one of the leading preventable causes of death, and prevalence among US adults now sits above 40% on recent national survey data, up sharply from the 36.5% figure that older articles still quote. The associated conditions are well documented: cardiovascular disease, stroke, type 2 diabetes, several cancers, obstructive sleep apnea, joint problems, and worse mental health outcomes.

Fat distribution also shifts with age and hormones. After 40, or after menopause, falling sex hormone levels tend to move fat toward the abdomen in men and toward the hips and thighs in women, which is why the same habits can produce a changing shape at a steady weight.

Changing the number

Fat loss requires an energy deficit, and roughly 3,500 calories of deficit corresponds to about a pound of fat, so 500 a day is the standard pound-a-week target. Aim for 0.5% to 1% of body weight a week; faster than that and an increasing share of what you lose is muscle.

Three things protect lean mass while the fat comes off. Eat enough protein, around 1.6 to 2.2 grams per kilogram of body weight, which is 115 to 160 grams for a 160 lb person. Lift weights, because resistance training tells the body to keep the muscle it has. And sleep, since short sleep raises appetite hormones and makes adherence far harder. The Calorie Calculator sets the intake target and the BMR Calculator shows what you burn at rest.

Spot reduction does not work. You cannot choose where fat comes off; that is set by genetics and hormones, and the abdominal region is often the last to respond. What you can control is the deficit and the training.

When the number is too low

Dropping to or below the essential range carries real consequences: hormonal disruption, loss of menstrual periods, reduced bone density, poor immune function, constant cold, and impaired recovery. In athletes this is recognised as relative energy deficiency in sport. Bodybuilders reaching 4% or 5% for a stage appearance hold it for days, not as a way of living. If your reading sits near the essential range, that is a conversation for a doctor rather than a target to defend.

Reading your results

The panel gives the Navy estimate first, then your category, the split between fat mass and lean mass, the Jackson and Pollock ideal for your age, and how much fat you would need to lose to reach it. Lean mass is the figure worth watching over a cut: if it is falling alongside fat mass, you are losing muscle and the deficit is too aggressive.

The donut shows that split visually. The line chart plots the ideal percentage for each age against your current reading, so you can see whether you sit above or below the target and by how much, and the table underneath places you in the American Council on Exercise categories with your own row highlighted. Re-measure monthly rather than daily. Body fat moves slowly, and the noise in any tape measurement is larger than a week of genuine change.