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Body Fat Calculator

Updated Feb 2026 Used 633 times
Deurenberg uses BMI, age, and sex; Navy uses tape measurements.
The published equations use sex-specific coefficients.
The BMI-and-age equation is intended for adults; use the same method when tracking change.
Supported base range: 1.2 to 2.3 m.
Weight is used for BMI, fat mass, and lean mass.
Measure just below the larynx without compressing the skin.
Follow the cited Navy measurement protocol and keep the tape level.
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 used

How the body-fat estimate is builtThe selected method is calculated independently; the result is then applied to body weight for component-mass estimates.
Normalize inputsUnits follow the selected equation SI / inches
Apply one methodMethods are not averaged BMI or tape
Estimate body fatScreening estimate %
Derive massesComponents sum to body weight fat + lean
How this estimate is builtReview the method and calculation version.
Versioned calculationFormula v3.0.0

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.

Result actions
1
Calculate BMINormalize height and weightkg / m^2
2
Apply the equationUse BMI, age, and sex coefficientPublished adult model
3
Estimate massesApply percentage to body weightFat mass and lean mass
1
Normalize lengthsConvert all measurements to inchesOne unit path
2
Apply tape equationUse the sex-specific log10 formulaCircumference difference
3
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

Keep exploring

4 available tools
BMI CalculatorScreen weight relative to height.Navy Body Fat CalculatorUse the dedicated circumference workflow.Calorie Deficit CalculatorEstimate an initial energy target.Protein CalculatorEstimate an adult protein range.
Public verification recordFormula v3.0.0
Review scope
Adult Deurenberg BMI-and-age And U.S. Navy Circumference Estimates With Derived Masses
Review team
CalculatorGeek Algorithmic Team
Verified
2026-09-10
Next source review
2027-09-10
Automated fixtures
6 cases

Review method

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

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.

Primary sources

Latest 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.

Published calculation checks

CaseInputsExpected 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
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.

Continue with Understand fat and lean mass or Track body fat consistently for the next calculation.

How to use the calculator

  1. Select the method you intend to use.
  2. Enter age, sex, height, weight, and any circumferences required by that method.
  3. Measure on bare skin or thin clothing without compressing the tape.
  4. Calculate, then record the method, units, date, and conditions with the result.
  5. 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.

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.

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.