Body Fat Calculator

Updated Sep 2026 Used 637 times

Use the Body Fat Calculator to calculate and interpret estimated body fat.

Calculation method

Deurenberg uses BMI, age, and sex; Navy uses tape measurements.

Sex used by the equation

The published equations use sex-specific coefficients.

Age

The BMI-and-age equation is intended for adults; use the same method when tracking change.

Height

Supported base range: 1.2 to 2.3 m.

Body weight

Weight is used for BMI, fat mass, and lean mass.

Neck circumference

Measure just below the larynx without compressing the skin.

Waist circumference

Follow the cited Navy measurement protocol and keep the tape level.

Hip circumference

For the female Navy equation, measure at the widest point of the hips.

Guest calculations stay on this device. Signed-in results sync privately.

Your result

Estimated body fat

Enter your values, then calculate to see a verified result.

Inputs usedReview the information used for this result.

Full calculation and sourcesReview the equation, normalized inputs, assumptions, and version.

Versioned calculationFormula v3.0.1

What is estimated

Body-fat percentage plus fat and lean mass. This does not directly measure tissue or diagnose health.

Methods supported

The adult Deurenberg BMI-and-age equation and the sex-specific U.S. Navy circumference equation.

Important limitation

Tape technique and population differences can move the estimate more than the displayed decimal.

Calculate BMINormalize height and weightkg / m^2

Apply the equationUse BMI, age, and sex coefficientPublished adult model

Estimate massesApply percentage to body weightFat mass and lean mass

Normalize lengthsConvert all measurements to inchesOne unit path

Apply tape equationUse the sex-specific log10 formulaCircumference difference

Compare methodsShow the BMI-and-age estimate separatelyDo not average them

Interpretation

The selected method estimates .

Fat mass and lean mass are derived from the same estimated percentage.

Use consistent measurements and method when tracking change.

Use this result

Lean Mass Headroom CalculatorRun a user-controlled FFMI scenario.Body Shape Ratio CalculatorCompare apparel proportions without a medical body-type claim.GLP-1 Body Composition Change CalculatorCompare two lean-mass estimates without causal prediction.

Body Fat Calculator: purpose and method

Calculates estimated body fat, estimated fat mass, estimated lean mass, and BMI used by the estimate from calculation method, sex used by the equation, age, and height with visible method, validation, precision, and limitations.

Keep exploring

4 related pages

Method and test recordFormula v3.0.1

Recorded scope: Adult Deurenberg BMI-and-age and U.S. Navy circumference estimates with derived masses
Publisher: CalculatorGeek
Reviewed by: CalculatorGeek Editorial Team
Recorded review date: 2026-09-10
Next source review: 2027-09-10
Definition fixtures: 6 configured scenarios
Published examples: 6 shown below

Recorded method

The team checked equation provenance, sex coefficients, unit normalization, logarithm boundaries, derived masses, package examples, and browser behavior.

These records describe the published model and reference tests. A test-case count is not a certification of every possible input or an independent specialist review. Editorial policy

Known limitations

Both methods estimate body fat; neither directly measures tissue or visceral fat.
Tape placement, tension, posture, breathing, hydration, and population differences can change the estimate.
The tool is intended for adults and is not a diagnosis or universal category standard.

Method sources

Latest model update

2026-09-09 - Imported the final primary-page copy and complete six-article content cluster from the September 9 Markdown package without altering calculator logic.

Reference inputs and expected results

These published examples are separate from the configured definition fixtures and any additional automated assertions. Expected values use the stated output units; invalid inputs are intended to be rejected.

Case	Inputs	Expected result
Deurenberg adult male at BMI 25	{"method":{"value":"deurenberg"},"sex":{"value":"male"},"age":{"value":30,"unit":"years"},"height":{"value":180,"unit":"cm"},"weight":{"value":81,"unit":"kg"}}	{"bmi":25,"body_fat":20.7,"fat_mass_kg":16.8,"lean_mass_kg":64.2}
Deurenberg adult female at BMI 25	{"method":{"value":"deurenberg"},"sex":{"value":"female"},"age":{"value":30,"unit":"years"},"height":{"value":180,"unit":"cm"},"weight":{"value":81,"unit":"kg"}}	{"bmi":25,"body_fat":31.5}
Navy male package example	{"method":{"value":"navy"},"sex":{"value":"male"},"age":{"value":30,"unit":"years"},"height":{"value":70,"unit":"in"},"weight":{"value":180,"unit":"lb"},"neck":{"value":15,"unit":"in"},"waist":{"value":36,"unit":"in"}}	{"body_fat":21.25,"fat_mass_lb":38.25,"lean_mass_lb":141.75}
Navy male metric equivalence	{"method":{"value":"navy"},"sex":{"value":"male"},"age":{"value":30,"unit":"years"},"height":{"value":177.8,"unit":"cm"},"weight":{"value":81.6466266,"unit":"kg"},"neck":{"value":38.1,"unit":"cm"},"waist":{"value":91.44,"unit":"cm"}}	{"body_fat":21.25}
Navy female requires hip	{"method":{"value":"navy"},"sex":{"value":"female"},"age":{"value":30,"unit":"years"},"height":{"value":165,"unit":"cm"},"weight":{"value":65,"unit":"kg"},"neck":{"value":34,"unit":"cm"},"waist":{"value":78,"unit":"cm"}}	Accessible validation error
Invalid Navy logarithm relationship	{"method":{"value":"navy"},"sex":{"value":"male"},"age":{"value":30,"unit":"years"},"height":{"value":170,"unit":"cm"},"weight":{"value":70,"unit":"kg"},"neck":{"value":50,"unit":"cm"},"waist":{"value":45,"unit":"cm"}}	Accessible validation error

Report an issue with this tool. Include the page URL, units, expected answer, and steps to reproduce. Do not include sensitive personal information.

On this page

Direct answer

A body-fat calculator estimates what share of total body weight is fat. A circumference method uses measurements such as waist, neck, hip, and height. A BMI-based method uses height, weight, age, and sex in a population equation. Because the methods use different inputs and assumptions, two estimates can disagree without either calculation being broken.

For the next related calculation, use the Skinfold Body Fat Calculator. Use Jackson-Pollock 3-site or 7-site measurements.

Continue this workflow with the Lean Mass Headroom Calculator. Run a user-controlled FFMI scenario.

How to use the calculator

Select the method you intend to use.
Enter age, sex, height, weight, and any circumferences required by that method.
Measure on bare skin or thin clothing without compressing the tape.
Calculate, then record the method, units, date, and conditions with the result.
Repeat under the same conditions when tracking change.

If you select a circumference method, review How to Measure Body Fat at Home before relying on a small change.

To compare this result with another relevant method, open the Lean Body Mass Calculator. Compare Boer, James, and Hume lean-body-mass estimates.

Formula and methodology

U.S. Navy circumference method

The commonly used adult male equation in inches is:

body fat % = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76

The commonly used adult female equation in inches is:

body fat % = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387

All lengths must use the unit expected by the selected equation. The calculator should normalize units before calculation and never mix inch constants with centimeter inputs.

BMI-and-age estimation

The adult Deurenberg-style equation is commonly written:

body fat % = 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4

where sex = 1 for male and 0 for female in the original equation. This is a population estimate. The live interface must not attribute it to an organization unless its source supports that attribution. CDC explains that BMI is not a direct measure of body fat and cannot distinguish fat from muscle or bone.

Worked examples

For a male input of 70 in height, 36 in waist, and 15 in neck:

86.010 × log10(36 − 15) − 70.041 × log10(70) + 36.76 ≈ 21.25%

At 180 lb, estimated fat mass is 180 × 0.2125 = 38.25 lb, and estimated lean mass is 180 − 38.25 = 141.75 lb.

For a 30-year-old male with BMI 25, the Deurenberg-style equation gives:

1.20 × 25 + 0.23 × 30 − 10.8 − 5.4 = 20.7%

The arithmetic can be exact while the biological estimate remains uncertain.

Precision and rounding

Keep full internal precision through the equation, convert the final percentage to a fraction for mass arithmetic, and round only displayed outputs. Do not round BMI, logarithms, or circumference differences early. Extra decimal places do not create clinical accuracy.

Interpret the result carefully

Category charts differ by source, age, sex classification, population, and purpose. A fitness category is not a diagnosis and does not identify visceral fat. Read the Body Fat Percentage Chart Guide before treating a label as a target.

If two methods disagree, do not average them. Check inputs, choose one repeatable method, and use U.S. Navy vs BMI Body Fat Methods to understand the difference.

Accuracy and limitations

Tape placement, tension, posture, breathing, hydration, meals, exercise, and time of day can move the estimate.
BMI-based equations may misclassify people whose muscularity or proportions differ from the development sample.
Circumference equations estimate total body fat; they do not directly measure visceral fat.
BIA scales can vary with hydration and device algorithm.
This calculator is intended for adults. Children, pregnancy, edema, major fluid shifts, and clinical conditions require an appropriate professional method.

Read Body Fat Calculator Accuracy before using small changes for a health or training decision.

Inputs, outputs and result meaning

Inputs

Calculation method: Deurenberg uses BMI, age, and sex; Navy uses tape measurements. Available choices are BMI-and-age estimate (Deurenberg) and U.S. Navy circumference method.
Sex used by the equation: The published equations use sex-specific coefficients. Available choices are Male and Female.
Age: The BMI-and-age equation is intended for adults; use the same method when tracking change. Supported units include years (yr). The supported range is 18 through 80.
Height: Supported units include centimeters (cm), meters (m), inches (in), feet (ft), and feet / inches (ft / in). The supported range is 1.2 through 2.3.
Body weight: Weight is used for BMI, fat mass, and lean mass. Supported units include grams (g), kilograms (kg), and pounds (lb). The supported range is 30 through 300.
Neck circumference: Measure just below the larynx without compressing the skin. Supported units include meters (m), centimeters (cm), and inches (in). The supported range is 0.2 through 0.7.
Waist circumference: Follow the cited Navy measurement protocol and keep the tape level. Supported units include meters (m), centimeters (cm), and inches (in). The supported range is 0.4 through 2.2.
Hip circumference: For the female Navy equation, measure at the widest point of the hips. Supported units include meters (m), centimeters (cm), and inches (in). The supported range is 0.5 through 2.2.

Outputs

Estimated body fat: This is the primary result. It is displayed in %. The visible value uses up to 1 decimal places according to the output rule.
Estimated fat mass: It is displayed in kg. The visible value uses up to 1 decimal places according to the output rule. The same result may be available in another supported unit or display mode.
Estimated lean mass: It is displayed in kg. The visible value uses up to 1 decimal places according to the output rule. The same result may be available in another supported unit or display mode.
BMI used by the estimate: The visible value uses up to 1 decimal places according to the output rule.
BMI-and-age comparison: It is displayed in %. The visible value uses up to 1 decimal places according to the output rule. It appears only when the selected mode supports this result.
Difference between methods: It is displayed in percentage points. The visible value uses up to 1 decimal places according to the output rule. It appears only when the selected mode supports this result.

Body fat % = 1.20 x BMI + 0.23 x age - 10.8 x sex - 5.4. Keep the result label, unit, selected mode, and stated limitations together when sharing the answer.

Frequently asked questions

Is an online body-fat calculator accurate?

It can produce a consistent estimate when inputs and technique are consistent, but it is not a direct measurement. Accuracy depends on the method, population equation, and input quality.

Which method should I use?

Use the Navy method when you can take repeatable circumferences. Use a BMI-based method when only height, weight, age, and sex are available, while accepting its broader assumptions. Keep the same method for trends.

Why does my smart scale differ?

Most smart scales use bioelectrical impedance and proprietary prediction models. Hydration, recent exercise, meals, skin temperature, and device assumptions can change the result.

How often should I check?

Choose an interval long enough for expected change to exceed day-to-day noise. Many users compare every two to four weeks under standardized conditions.

Sources

Evidence and editorial status

Evidence for this package was checked on September 10, 2026. This material is educational and is not medical diagnosis, treatment, or individualized nutrition advice.