Body Fat Calculator

Choose circumference when you can take the required tape measurements consistently. Choose BMI estimate when circumference measurements are unavailable.

Select metric or imperial units and the male or female coefficient used by the published equation.

Enter every visible field. The result shows estimated body-fat percentage, fat mass, fat-free mass, FFMI, BMI, and a general reference band.

For trend tracking, repeat the same method under similar conditions rather than comparing small changes from different methods.

The legacy circumference equation estimates body fat from external body shape. The male equation uses height, neck, and abdomen at the navel. The female equation uses height, neck, natural waist, and hips.

The BMI regression estimates body fat from BMI, adult age, and a male or female coefficient. It does not use circumference or directly account for muscularity and fat distribution.

Neither method is reliably best for every individual. Measurement quality, body shape, age, population, and the original equation assumptions all matter.

Use a flexible non-stretch tape on bare skin where practical. Keep it horizontal and snug without compressing the tissue.

Measure the neck just below the larynx.

For the male equation, measure the abdomen horizontally at the navel after a normal relaxed exhalation.

For the female equation, measure the natural waist after a relaxed exhalation and the widest part of the hips and buttocks.

Repeat each measurement using the same landmarks and tape tension.

Body-fat percentage estimates how much total body weight consists of fat mass.

Fat-free mass is everything remaining after estimated fat mass is removed. It includes muscle but is not a measurement of muscle alone.

FFMI adjusts estimated fat-free mass for height. BMI describes total weight relative to height and remains different from both body-fat percentage and FFMI.

The visual scale uses commonly cited adult fitness categories associated with the American Council on Exercise.

Neutral labels are added below the essential-fat minimum and above the average range.

These bands are not diagnoses, treatment thresholds, competition requirements, or universal definitions of health.

Lower body fat is not automatically better. Essential fat supports normal physiological function.

The adult equation is BF% = 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4, with male coded as 1 and female as 0.

The original study reported a standard error of estimate of approximately 4.1 body-fat percentage points.

That value describes prediction error across the study and does not guarantee that an individual estimate is within 4.1 points.

The study population covered BMI values from approximately 13.9 to 40.9 and ages up to 83.

The circumference option uses older equations commonly described online as the U.S. Navy body-fat method.

The current June 2026 Navy Guide-4 collects height, waist, and weight.

Step 1 uses waist-to-height ratio. Sailors at or above the specified ratio proceed to a separate body-composition calculation based on height-waist difference, weight, and sex-specific official tables.

This calculator does not implement that procedure and cannot determine Navy standards or compliance.

FFMI equals estimated fat-free mass in kilograms divided by height in metres squared.

It can provide height-adjusted context when BMI is elevated partly by muscularity.

FFMI depends on the body-fat estimate and is not a health grade, training classification, universal natural limit, or test for performance-enhancing drug use.

Circumference equations, BMI regressions, bioelectrical-impedance scales, skinfolds, DXA, air-displacement methods, and multi-compartment models measure or infer body composition differently.

Hydration, recent food and exercise, equipment equations, technician skill, and tape placement can change a result.

A small difference between two estimates does not prove that body fat or muscle changed.

The calculation runs entirely in the browser.

Age, height, weight, neck, waist, abdomen, hip, and result values are not uploaded, added to a public URL, or permanently stored.

Use the estimate as broad context rather than a diagnosis, personalised target, treatment plan, or military-compliance result.