Body Fat Calculator

Estimate adult body-fat percentage with three anthropometric methods: a legacy circumference equation commonly called the Navy method, Relative Fat Mass using height and waist circumference, or CUN-BAE using BMI, age, and sex. Review estimated fat mass, fat-free mass, FFMI, BMI, general adult reference bands, and important limitations.

How to use the Body Fat Calculator

Choose the estimation method that matches the measurements you can take reliably.

Circumference uses height, neck, and abdomen or waist measurements, with hips required for the female equation. RFM uses height and waist circumference. CUN-BAE uses height, weight, age, and sex.

Weight is also used to calculate estimated fat mass, fat-free mass, BMI, and FFMI even when it is not part of the selected body-fat percentage equation.

Choose Metric or Imperial, enter the visible measurements, and the result updates automatically.

For trend tracking, use the same method and take measurements in a consistent way rather than comparing small differences from several different methods.

Which body-fat estimation method should you use?

No anthropometric equation is reliably most accurate for every individual.

Circumference uses the most body-shape measurements but is sensitive to exact tape placement. RFM needs only height and waist circumference for the body-fat estimate. CUN-BAE does not need circumference measurements but relies on BMI, age, and sex.

The methods were developed from different populations and mathematical models, so they can produce noticeably different results for the same person.

For personal trend tracking, consistency is usually more informative than switching equations to find the number you prefer.

**Body-fat estimation methods**
Method	Inputs	Useful for	Important limitation
Circumference	Height, weight, neck, and abdomen or waist; hips for the female equation	A tape-measure estimate that incorporates body shape	Sensitive to tape placement and not the current official U.S. Navy BCA
Relative Fat Mass (RFM)	Height, waist circumference, weight, and the published male or female coefficient	A simpler waist-based estimate without neck or hip measurements	A population equation; individual body shape and waist measurement technique still matter
CUN-BAE	Age, height, weight, and the published male or female coefficient	An estimate when circumference measurements are unavailable	A population regression rather than a direct body-composition measurement

Circumference body-fat estimate

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

For the male equation, the body-fat percentage calculation uses height, neck circumference, and abdomen circumference measured at the navel.

For the female equation, it uses height, neck circumference, natural waist circumference, and hip circumference.

Weight is not part of the percentage equation itself, but Olivez uses body weight to calculate estimated fat mass, fat-free mass, BMI, and FFMI.

How to take circumference measurements

Use a flexible, non-stretch measuring tape and measure consistently at the same anatomical landmarks.

Keep the tape level and snug without compressing the underlying tissue.

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

For the legacy female equation, use the natural waist and measure the hips around their widest point.

Small differences in location, posture, breathing, and tape tension can change the estimate.

Why this is not the current U.S. Navy BCA

The current U.S. Navy Body Composition Assessment is different from the older neck-based equations commonly found in online body-fat calculators.

The June 2026 Navy Guide-4 collects height, waist circumference at the umbilicus, and body weight.

Its first step evaluates waist-to-height ratio. When a second assessment step is required, the current process uses height-waist difference, body weight, and sex-specific official tables or PRIMS calculations.

Oliv ez does not implement that official assessment and this calculator cannot determine Navy compliance.

Relative Fat Mass (RFM)

Relative Fat Mass estimates whole-body fat percentage from height, waist circumference, and sex.

The adult equation is BF% = 64 − 20 × height ÷ waist + 12 × sex, where male is coded as 0 and female as 1.

Height and waist circumference must use the same unit, so centimetres divided by centimetres and inches divided by inches produce the same ratio.

The original RFM study developed the equation using a large adult NHANES sample and validated it against DXA-measured body-fat percentage in a separate sample.

RFM remains an estimate. Better performance than BMI in a study population does not make an individual RFM value equivalent to a direct body-composition measurement.

CUN-BAE body-fat estimate

CUN-BAE, short for Clínica Universidad de Navarra–Body Adiposity Estimator, predicts body-fat percentage from BMI, age, and sex.

Its published equation contains BMI, BMI squared, age, sex, and interaction terms rather than using a simple fixed conversion from BMI.

The original development study included 6,510 adults aged 18 through 80 and was separately validated in another 1,149 participants.

The reported standard error of estimate was approximately 4.7 body-fat percentage points. That describes prediction error across a study population and is not a guaranteed individual error margin.

What your results mean

Estimated body-fat percentage is the proportion of total body weight the selected equation predicts to be fat mass.

Estimated fat mass applies that percentage to total body weight.

Fat-free mass is everything remaining after estimated fat mass is removed. It includes skeletal muscle, but also bone, organs, connective tissue, water, and other non-fat tissue.

FFMI adjusts estimated fat-free mass for height. BMI instead uses total body weight, so BMI and FFMI describe different things.

**What each result means**
Result	Meaning
Estimated body-fat percentage	Estimated fat mass as a percentage of total body weight
Estimated fat mass	Body weight multiplied by the displayed body-fat estimate
Estimated fat-free mass	Body weight minus estimated fat mass; includes more than muscle
FFMI	Estimated fat-free mass adjusted for height
BMI	Total body weight relative to height; supporting context rather than a body-fat measurement
Reference band	A broad adult fitness reference rather than a diagnosis or personal target

General adult body-fat reference bands

The visual result uses commonly cited general adult fitness reference bands.

For men, the scale separates essential-fat, athlete, fitness, average, and higher reference ranges. The female bands use different boundaries because the published fitness references differ by sex.

These labels are broad fitness references rather than diagnostic categories, treatment thresholds, or universal definitions of health.

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

**General adult body-fat reference bands**
Reference band	Male	Female
Below essential-fat reference	Below 2%	Below 10%
Essential-fat range	2–5.9%	10–13.9%
Athlete range	6–13.9%	14–20.9%
Fitness range	14–17.9%	21–24.9%
Average range	18–24.9%	25–31.9%
Above general reference range	25% or higher	32% or higher

Fat mass and fat-free mass

Estimated fat mass equals total body weight multiplied by the displayed body-fat percentage.

Fat-free mass equals total body weight minus estimated fat mass.

These values do not become more accurate than the body-fat percentage they came from. If the percentage estimate is wrong, the derived fat and fat-free mass estimates will also be wrong.

What FFMI means

Fat-Free Mass Index divides estimated fat-free mass in kilograms by height in metres squared.

It provides height-adjusted context for estimated non-fat mass and can be useful when BMI is elevated partly because of muscularity.

FFMI still depends on an estimated body-fat percentage. It is not a diagnosis, universal muscularity score, proven natural limit, or test for performance-enhancing drug use.

Why body-fat methods disagree

Body-fat percentage cannot be determined precisely from BMI or a tape measurement alone. Each equation uses a different statistical relationship to estimate body composition.

The circumference method models external body shape. RFM uses waist relative to height. CUN-BAE uses BMI, age, and sex.

Bioelectrical-impedance scales, skinfold measurements, DXA, air-displacement methods, and multi-compartment models use different physical measurements and assumptions again.

Several methods can therefore produce different values on the same day without any actual change in body fat.

**Common sources of uncertainty**
Issue	Why it matters
Tape placement	Small differences in measurement site, angle, posture, breathing, or tape tension can change circumference-based estimates
Population equations	An equation can perform reasonably across a study population while being meaningfully wrong for one person
Different methods	Circumference equations, RFM, CUN-BAE, BIA, skinfolds, DXA, and other methods can return different values
Derived values	Fat mass, fat-free mass, FFMI, and the reference band inherit uncertainty from the underlying body-fat estimate
Trend tracking	Changes in measurement technique, hydration, food intake, exercise, and other conditions can obscure small real changes

Why your smart scale may show a different number

Most consumer body-composition scales use bioelectrical impedance rather than the anthropometric equations used here.

Their results can be affected by hydration, recent food and drink, exercise, skin contact, device equations, and other factors.

A difference between a smart scale and this calculator does not by itself show that either value is the person's exact body-fat percentage.

How to track body-fat estimates more consistently

Use the same estimation method each time.

When circumference is required, use the same tape, anatomical landmarks, posture, and tape tension.

Compare measurements under broadly similar conditions rather than treating every small day-to-day difference as a body-composition change.

Longer-term trends are generally more useful than small movements in a single estimated percentage.

Important limitations

This calculator estimates body composition from adult prediction equations. It does not directly measure fat tissue.

Prediction equations can be less representative when an individual's age, physiology, body shape, training status, or population background differs substantially from the people used to develop the equation.

The calculator is not designed for children, pregnancy-related assessment, eating-disorder treatment, medical diagnosis, military compliance, or another high-stakes decision.

Body-fat and body-composition formulas

The selected equation first estimates body-fat percentage. Olivez displays that estimate to one decimal place and uses the same percentage for the derived body-mass values.

Legacy circumference equation — male

B F = 86.010 lo g_{10} (Abd - N) - 70.041 lo g_{10} (H) + 36.76

Legacy circumference equation — female

B F = 163.205 lo g_{10} (W + H i p - N) - 97.684 lo g_{10} (H) - 78.387

Relative Fat Mass

B F = 64 - 20 (\frac{H}{W a}) + 12 S

CUN-BAE

B F = - 44.988 + 0.503 (A g e) + 10.689 S + 3.172 (B M I) - 0.026 (B M I)^{2} + 0.181 (B M I) S - 0.020 (B M I) (A g e) - 0.005 (B M I)^{2} S + 0.00021 (B M I)^{2} (A g e)

Estimated fat mass

F M = \frac{B F}{100} \times W e i g h t

Estimated fat-free mass

F F M = W e i g h t - F M

Fat-Free Mass Index

F F M I = \frac{F F M _{k g}}{H _{m}^{2}}

Body Mass Index

B M I = \frac{W _{k g}}{H _{m}^{2}}

$B F$: Estimated body-fat percentage
$A b d$: Male abdomen circumference in inches in the legacy circumference equation
$W$: Female natural-waist circumference in inches in the legacy circumference equation
$N$: Neck circumference in inches
$H i p$: Hip circumference in inches
$H$: Height in inches for the legacy circumference equations, or height in the same unit as waist for RFM
$W a$: Waist circumference in the same unit as height for RFM
$S$: Published sex coefficient: 0 for male and 1 for female in RFM and CUN-BAE
$A g e$: Age in years in CUN-BAE
$B M I$: Body Mass Index in CUN-BAE
$F M$: Estimated fat mass
$F F M$: Estimated fat-free mass
$F F M I$: Fat-Free Mass Index

Examples

Male circumference estimate

Male coefficient; height 180 cm; weight 82 kg; neck 40 cm; abdomen 86 cm.

Estimated body fat is 15.3%. Estimated fat mass is 12.5 kg, fat-free mass is 69.5 kg, BMI is 25.3, and FFMI is 21.4 kg/m².

Weight is used for the derived mass values, BMI, and FFMI.

Relative Fat Mass estimate

Male coefficient; height 180 cm; weight 82 kg; waist circumference 86 cm.

RFM estimates body fat at 22.1%. Estimated fat mass is 18.1 kg, fat-free mass is 63.9 kg, BMI is 25.3, and FFMI is 19.7 kg/m².

RFM itself uses height, waist circumference, and sex. Weight supplies the derived body-mass results.

Female CUN-BAE estimate

Female coefficient; age 32; height 165 cm; weight 68 kg.

BMI is approximately 25.0 and CUN-BAE estimates body fat at 34.4%. Estimated fat mass is 23.4 kg, fat-free mass is 44.6 kg, and FFMI is 16.4 kg/m².

CUN-BAE uses BMI, age, and sex rather than circumference measurements.

Why methods can disagree

Male coefficient; age 32; height 180 cm; weight 82 kg; neck 40 cm; waist or abdomen 86 cm.

The legacy circumference equation estimates 15.3% body fat, RFM estimates 22.1%, and CUN-BAE estimates 22.8%.

The methods model body composition differently. Their disagreement is a useful reminder that these are estimates rather than direct measurements.

Fat-free mass is not muscle mass

Body weight 80 kg and estimated body fat 20.0%.

Estimated fat mass is 16.0 kg and estimated fat-free mass is 64.0 kg.

The 64.0 kg also includes bone, organs, water, connective tissue, and other non-fat components.

Frequently Asked Questions

Which body-fat method should I use?

Use Circumference when you can take the required tape measurements consistently. RFM is simpler when you can measure waist circumference. CUN-BAE is useful when you only have age, height, and weight. No method is guaranteed to be most accurate for every individual.

Which body-fat calculator method is most accurate?

There is no single anthropometric equation that is most accurate for every person. Accuracy depends on body shape, population, age, measurement technique, and the reference method used to develop or validate the equation.

What is Relative Fat Mass?

Relative Fat Mass, or RFM, is an adult body-fat estimation equation based on height relative to waist circumference and a male or female coefficient.

Does RFM require body weight?

The RFM percentage equation itself does not use body weight. Olivez asks for weight so it can also calculate estimated fat mass, fat-free mass, BMI, and FFMI.

What is CUN-BAE?

CUN-BAE is a published body-adiposity estimator that predicts adult body-fat percentage from BMI, age, and sex.

Why does CUN-BAE require age?

Age is part of the published regression because the statistical relationship between BMI and body-fat percentage changes across adulthood.

Why is CUN-BAE limited to ages 18 through 80?

The original development population covered adults aged 18 through 80. The calculator does not extend the public CUN-BAE option beyond that range as though it had been validated there.

How accurate is CUN-BAE?

The original study reported a standard error of estimate of about 4.7 body-fat percentage points. That is a study-level prediction statistic rather than a guaranteed personal error margin.

Is the circumference method the current official U.S. Navy body-fat test?

No. It uses older neck-based equations commonly called the Navy method. The June 2026 Navy Body Composition Assessment uses height, waist circumference at the umbilicus, and weight in a different assessment process.

Can this calculator tell me whether I pass Navy standards?

No. It does not implement the current official Navy assessment tables, rounding rules, or PRIMS process and cannot determine military compliance.

Can I use pounds and inches?

Yes. Choose Imperial. Height is entered in feet and inches, circumference measurements use inches, and weight uses pounds.

Why does neck size affect the circumference estimate?

Neck circumference is one of the terms in the legacy circumference equation. That is one reason people with different body shapes can receive different estimates even when height and waist measurements are similar.

What is fat mass?

Estimated fat mass is body weight multiplied by the estimated body-fat percentage.

What is fat-free mass?

Fat-free mass is body weight minus estimated fat mass. It includes muscle, bone, organs, connective tissue, water, and other non-fat components.

Is fat-free mass the same as muscle mass?

No. Skeletal muscle is only one component of fat-free mass.

What is FFMI?

FFMI is estimated fat-free mass in kilograms divided by height in metres squared. It provides height-adjusted context for estimated non-fat mass.

Can FFMI prove steroid use?

No. FFMI is not a drug-use test and also inherits uncertainty from the underlying body-fat estimate.

Why is my smart-scale body-fat percentage different?

Most consumer body-composition scales use bioelectrical impedance rather than the equations used here. Hydration, recent food and drink, exercise, contact quality, and the device's own algorithm can all affect the result.

Why do the three methods give different results?

They use different measurements and statistical models. Circumference models external body shape, RFM uses height relative to waist circumference, and CUN-BAE uses BMI, age, and sex.

Are the body-fat reference bands medical diagnoses?

No. They are broad adult fitness references and should not be treated as universal health thresholds, diagnoses, or treatment targets.

Is lower body fat always better?

No. Essential body fat supports normal physiological functions, and appropriate body composition varies among individuals.

Can children use this Body Fat Calculator?

The calculator is designed around adult prediction equations and adult reference bands. Children and adolescents require age-appropriate body-composition assessment.

Can I use this calculator during pregnancy?

These equations and adult fitness reference bands are not designed to assess pregnancy-related changes in body composition.