Which measurements does each formula use?

The historical Navy model uses height, neck and waist, plus hip for the female equation. Weight is optional and supplies estimated fat and fat-free mass. The adult Deurenberg formula needs height, weight, age and sex. The Navy equation does not use age. When supplied, age must be 18–83 on this adult-only page; child and teenage assessments are unsupported.

How are these body-fat estimates calculated?

The Navy estimate computes body density from base-10 logarithms of centimetre measurements, then converts it with 495 ÷ density − 450. The adult Deurenberg equation is 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4, where male = 1 and female = 0; BMI is kilograms divided by metres squared. The substituted arithmetic appears beside each estimate. Inches and pounds are converted before using the same equations, so switching units does not choose a different model.

How accurate are the results?

These are estimates from measured inputs and population equations. The original 1991 Deurenberg study reported a 4.1-percentage-point standard error of estimate against densitometry, not a guaranteed error bound for an individual or a DEXA comparison. Tape placement and differences in body shape affect the Navy estimate. Showing one decimal does not establish that level of measurement accuracy. See the original study at https://doi.org/10.1079/BJN19910073.

Where do I measure neck, waist and hips?

Measure neck just below the larynx, with the tape sloping slightly down at the front. For the male equation, measure waist horizontally at the navel; for the female equation, use the narrowest waist and the widest hips. Keep the tape snug without compressing and use a normal relaxed exhale. Waist minus neck (male), or waist plus hip minus neck (female), must be positive for the logarithm.

Why do the two methods disagree?

The circumference equation models body shape; the BMI equation uses height, weight, age and sex. BMI does not separate muscle from fat, and the circumference model does not directly measure fat. A difference does not identify which estimate is correct. Their span is not a measured range or confidence interval.

What do the chart and lean-mass values mean?

The chart reproduces the American Council on Exercise general reference table for men and women. It is not an age-specific healthy, ideal or recommended target and does not diagnose a person. The source table uses whole percentages; this page extends each band to the next boundary for one-decimal estimates and adds a below-table row. Fat mass = body weight × displayed body-fat percentage ÷ 100; fat-free or lean mass = weight − estimated fat mass. Fat-free mass includes water, bone and organs as well as muscle. One-decimal mass displays can differ by 0.1 from the rounded total.

Can this calculate military standards, skinfolds or weight-loss goals?

This page supplies historical Navy and adult BMI estimates only. It does not implement current Army, Air Force, Marine Corps or Navy assessment procedures, measurement rounding, exemptions or pass/fail limits. It has no caliper/skinfold, photo/AI, scale, waist-only, ethnic-specific, child or teenage model; no muscle/water breakdown, calorie/BMR/TDEE/macro calculation, health target or goal-weight prescription.

Can I use metric or imperial measurements?

Yes. Bare lengths follow the centimetre/inch toggle; bare weights follow kilograms/pounds. Explicit units such as 80 kg, 175 lb, 180 cm or 5 ft 10 in take precedence. Metres and millimetres also convert correctly. Decimal commas are accepted except three-digit comma groups, which mean thousands; use a decimal point when that convention is ambiguous.

Are my measurements uploaded or saved?

Calculations run locally in the browser. Tool measurement values are not sent by the analytics adapter. Restoration is read-only; deliberate valid edits can be saved in this browser, while invalid drafts keep the previous saved entry. An unusable entry is retained until you choose Forget saved measurements. Copy result includes both model results or their missing-field messages, inputs and limitations.

Body Fat Percentage Calculator

Compare two adult body-fat estimates: the historical Navy circumference/body-density equation with the Siri conversion, and the Deurenberg equation using BMI, age and sex. Their difference is a model comparison, not a confidence interval or a health target.

US Navy method · MaleReadyEnter height, neck and waist to get a reading

Method

Sex

Units

Height

Neck

Waist

Weight

Age

Adult estimates only (18–83 years when age is supplied). The Navy method does not need age. These formulas estimate total fat, not visceral fat, water or muscle separately. Fat-free mass includes water, bone and organs.

Every box feeds both methods at once. The Navy side reads height, neck and waist; the BMI side reads height, weight and age. Fill in all of them and the two estimates appear together. Typing the unit yourself, “80 kg”, “180 cm”, “5'10"”, always beats the toggle.

Two separate estimates. Tape circumferences and BMI use different models. Their difference does not identify which is correct, and their span is not a confidence interval. No health target, weight-loss plan, exact instrument reading or military pass/fail is calculated.

The bands these categories come from

American Council on Exercise reference table for men. This table is not a health assessment or an age-specific target. Its source uses whole percentages; this calculator extends each band to the next boundary for one-decimal results and adds a below-table row.

Category	Body fat	This reading
Below essential fat	under 2%
Essential fat	2–5.9%
Athletic	6–13.9%
Fitness	14–17.9%
Average	18–24.9%
Obese	25% and above

Common questions

Which measurements does each formula use?: The historical Navy model uses height, neck and waist, plus hip for the female equation. Weight is optional and supplies estimated fat and fat-free mass. The adult Deurenberg formula needs height, weight, age and sex. The Navy equation does not use age. When supplied, age must be 18–83 on this adult-only page; child and teenage assessments are unsupported.
How are these body-fat estimates calculated?: The Navy estimate computes body density from base-10 logarithms of centimetre measurements, then converts it with 495 ÷ density − 450. The adult Deurenberg equation is 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4, where male = 1 and female = 0; BMI is kilograms divided by metres squared. The substituted arithmetic appears beside each estimate. Inches and pounds are converted before using the same equations, so switching units does not choose a different model.
How accurate are the results?: These are estimates from measured inputs and population equations. The original 1991 Deurenberg study reported a 4.1-percentage-point standard error of estimate against densitometry, not a guaranteed error bound for an individual or a DEXA comparison. Tape placement and differences in body shape affect the Navy estimate. Showing one decimal does not establish that level of measurement accuracy. See the original study at https://doi.org/10.1079/BJN19910073.
Where do I measure neck, waist and hips?: Measure neck just below the larynx, with the tape sloping slightly down at the front. For the male equation, measure waist horizontally at the navel; for the female equation, use the narrowest waist and the widest hips. Keep the tape snug without compressing and use a normal relaxed exhale. Waist minus neck (male), or waist plus hip minus neck (female), must be positive for the logarithm.
Why do the two methods disagree?: The circumference equation models body shape; the BMI equation uses height, weight, age and sex. BMI does not separate muscle from fat, and the circumference model does not directly measure fat. A difference does not identify which estimate is correct. Their span is not a measured range or confidence interval.
What do the chart and lean-mass values mean?: The chart reproduces the American Council on Exercise general reference table for men and women. It is not an age-specific healthy, ideal or recommended target and does not diagnose a person. The source table uses whole percentages; this page extends each band to the next boundary for one-decimal estimates and adds a below-table row. Fat mass = body weight × displayed body-fat percentage ÷ 100; fat-free or lean mass = weight − estimated fat mass. Fat-free mass includes water, bone and organs as well as muscle. One-decimal mass displays can differ by 0.1 from the rounded total.
Can this calculate military standards, skinfolds or weight-loss goals?: This page supplies historical Navy and adult BMI estimates only. It does not implement current Army, Air Force, Marine Corps or Navy assessment procedures, measurement rounding, exemptions or pass/fail limits. It has no caliper/skinfold, photo/AI, scale, waist-only, ethnic-specific, child or teenage model; no muscle/water breakdown, calorie/BMR/TDEE/macro calculation, health target or goal-weight prescription.
Can I use metric or imperial measurements?: Yes. Bare lengths follow the centimetre/inch toggle; bare weights follow kilograms/pounds. Explicit units such as 80 kg, 175 lb, 180 cm or 5 ft 10 in take precedence. Metres and millimetres also convert correctly. Decimal commas are accepted except three-digit comma groups, which mean thousands; use a decimal point when that convention is ambiguous.
Are my measurements uploaded or saved?: Calculations run locally in the browser. Tool measurement values are not sent by the analytics adapter. Restoration is read-only; deliberate valid edits can be saved in this browser, while invalid drafts keep the previous saved entry. An unusable entry is retained until you choose Forget saved measurements. Copy result includes both model results or their missing-field messages, inputs and limitations.

Adult estimates, not instrument measurements. Tape placement and body shape affect results; BMI cannot distinguish muscle from fat. No health assessment or military pass/fail.