Body Fat Calculator

Body-fat percentage is the estimated share of total body weight made up of fat mass. It can be useful body-composition context, but an online calculator does not directly measure tissue.

NexaCalc uses equation-based estimates and avoids universal diagnostic categories. Reference values vary by age, sex, population, sport, measurement method, and clinical context.

1. Choose Metric Units, US Units, or Other Units.
2. Select the sex coefficient and method: circumference, BMI-based, or compare both.
3. Enter age, height, and weight.
4. Add the circumference fields required by the selected sex coefficient when using the tape method.
5. Review warnings and compare methods without treating either result as exact.

The circumference method uses height and tape measurements. It is commonly associated with Navy-style circumference equations, but this page is not an official Navy, military, or compliance tool.

The BMI-based method uses the adult Deurenberg equation. It is an indirect prediction from BMI, age, and sex coefficient, not a direct body-composition measurement.

All circumference and height values are converted to inches before the circumference equation is applied. The BMI-based equation uses BMI from kilograms and meters.

These equations provide estimates and do not directly measure body composition.

Example 1: male coefficient, age 30, height 175 cm, weight 70 kg, neck 38 cm, abdomen 85 cm. Height converts to about 68.8976 in, neck to about 14.9606 in, and abdomen to about 33.4646 in. The circumference estimate is 17.0%, with estimated fat mass 11.9 kg and lean body mass 58.1 kg.

Example 2: male coefficient, age 30, height 175 cm, weight 70 kg. BMI is about 22.9. The adult Deurenberg BMI-based estimate is 18.1%.

Example 3: female coefficient, age 35, height 165 cm, weight 68 kg, neck 34 cm, waist 78 cm, hip 100 cm. The circumference estimate is 30.7%, with fat mass about 20.9 kg and lean body mass about 47.1 kg.

Example 4: US units, male coefficient, age 30, height 5 ft 9 in, weight 170 lb, neck 15 in, abdomen 34 in. The circumference result is 18.0%, the BMI-based result is 20.8%, and the method difference is 2.9 percentage points.

Measurement technique matters. Use a flexible, non-stretch tape, keep it level, and avoid compressing the skin. Use the same measurement approach when comparing results over time.

For the male equation, enter abdomen circumference at the navel, not a separate natural-waist value. For the female equation, enter natural waist and hip circumference separately.

Compare Both mode shows the circumference result and the BMI-based result side by side, along with the absolute difference in percentage points.

NexaCalc does not average the methods into a supposedly better result. Different methods can disagree because they use different inputs and assumptions.

Estimated fat mass is body weight multiplied by estimated body-fat percentage. Estimated lean body mass is the rest of body weight: muscle, bone, water, organs, and other non-fat tissue.

Lean body mass here is equation-derived. It should not be treated as a direct DEXA, MRI, hydrostatic weighing, or clinical measurement.

The BMI-based estimate starts with BMI. BMI is useful as a broad screening measure, but it cannot separate fat mass from lean mass. For direct BMI context, use the BMI Calculator.

The Deurenberg equation adds age and sex coefficient to BMI, but its prediction error can vary across body types and populations.

Body-fat equations may be less informative for children, teens, pregnancy, postpartum changes, athletes, highly muscular users, older adults, people with edema, people with substantial recent weight change, and medical conditions affecting body composition.

Lower body fat is not automatically healthier. Body composition should be considered with health history, physical function, nutrition, training, and professional assessment when accuracy matters.

This calculator is intended for adults 18 and older. It does not calculate adult body-fat estimates for users under 18.

Growth, puberty, and sex-specific development require age-appropriate assessment. Adult equations should not replace pediatric or adolescent guidance.

Body-fat estimates are body-composition context. Ideal Weight Calculator compares height-weight references, BMR Calculator estimates resting energy use, and TDEE Calculator estimates activity-adjusted daily energy expenditure.

• Hodgdon JA, Beckett MB. Prediction of Percent Body Fat for U.S. Navy Men from Body Circumferences and Height. Naval Health Research Center technical report, 1984. DOI link.
• Hodgdon JA, Beckett MB. Prediction of Percent Body Fat for U.S. Navy Women from Body Circumferences and Height. Naval Health Research Center technical report, 1984. DOI link.
• Potter AW, Tharion WJ, Holden LD, Pazmino A, Looney DP, Friedl KE. Circumference-Based Predictions of Body Fat Revisited: Preliminary Results From a US Marine Corps Body Composition Survey. Frontiers in Physiology. 2022. DOI link.
• Friedl KE, Vogel JA. Validity of Percent Body Fat Predicted from Circumferences: Classification of Men for Weight Control Regulations. Military Medicine. 1997;162(3):194-200. DOI link.
• Deurenberg P, Weststrate JA, Seidell JC. Body mass index as a measure of body fatness: age- and sex-specific prediction formulas. British Journal of Nutrition. 1991;65(2):105-114. DOI link.
• CDC. Adult BMI Categories: BMI is a screening measure and should be considered with other factors when assessing health. CDC source.
• Duren DL, Sherwood RJ, Czerwinski SA, Lee M, Choh AC, Siervogel RM, Chumlea WC. Body Composition Methods: Comparisons and Interpretation. Journal of Diabetes Science and Technology. 2008;2(6):1139-1146. DOI link.
• Kuriyan R. Body composition techniques. Indian Journal of Medical Research. 2018;148(5):648-658. DOI link.