Body Fat Calculator
Enter adult tape measurements for a historical circumference estimate, with no account and no values stored in the URL.
How to take the tape measurements
Stand normally and use a flexible, nonstretch tape. Keep it horizontal and snug without compressing skin, and read the tape after a normal exhale. Measure the neck just below the larynx. For the male-derived equation, measure the abdomen across the navel. For the female-derived equation, measure the natural waist at its narrowest point and the hips at their widest horizontal girth.
These landmarks provide one consistent consumer workflow from historical military procedures. They are not a promise that a home measurement matches a current service exam or a laboratory body-composition method. Small changes in placement or tension can noticeably change the estimate.
The study cited for the metric coefficients measured the male abdomen just above the iliac crest, a different location. This calculator uses the across-the-navel landmark documented in dated historical Navy training; that choice does not mean the coefficient study validated this location for every person.
Historical circumference equation
The calculator first converts all lengths to centimeters. The male-derived density equation is D = 1.0324 − 0.19077 log10(abdomen − neck) + 0.15456 log10(height). The female-derived density equation is D = 1.29579 − 0.35004 log10(waist + hips − neck) + 0.22100 log10(height). It then applies body-fat percentage = 495 ÷ D − 450.
Those coefficients come from a published metric formulation with historical Navy lineage. They describe relationships found in studied groups; they do not directly measure one person's fat tissue. Research summaries report errors of several percentage points in military samples, and the error for an individual can be different.
How to read the result
The large percentage is the equation output rounded half up to one decimal. If you enter weight, fat mass and lean mass are derived from the unrounded percentage and rounded separately. Lean mass means all nonfat mass, not muscle mass.
Body shape, ethnicity, muscle distribution, hydration, medical circumstances, and measurement technique can all affect how well a population equation fits one person. This educational estimate does not diagnose health, prescribe nutrition or exercise, establish a personal target, or determine current military eligibility.
Do not use this number alone for children or teens, pregnancy or postpartum, edema or other fluid shifts, eating-disorder care, or any decision that needs clinical assessment. A qualified clinician can help choose and interpret an appropriate method.
Private, browser-local calculation
The measurements and result stay in the current tab. They are not placed in the page URL, local storage, ToolNeko analytics, or a calculation-server request. The optional text summary is created by your browser only when you select Download TXT summary. Reset clears the form and result.
Frequently asked questions
What does this body fat calculator estimate?
It applies a historical circumference equation to adult tape measurements. The result is a population-derived estimate, not a direct measurement of body tissue and not a medical assessment.
Where should I place the tape?
Keep a flexible nonstretch tape horizontal and snug without compressing skin, and measure after a normal exhale. For the male-derived equation, measure the abdomen across the navel. For the female-derived equation, measure the natural waist at its narrowest and the hips at their widest. Measure the neck just below the larynx.
Why can another calculator differ by a tenth?
Sites may use different constants, unit handling, landmarks, or rounding. This page uses the published metric coefficients shown in the method section and rounds the final percentage half up to one decimal.
Does one decimal mean the estimate is precise?
No. One decimal makes repeated calculations readable; it does not remove equation or tape-placement error. Research in military samples found errors of several percentage points, and an individual's error can be different.
Is this the current Navy body composition assessment?
No. The equations have a historical military lineage, but current procedures can change and use different steps. Do not use this page for a service eligibility decision.
Can this diagnose health or set a personal goal?
No. It cannot diagnose a condition, prescribe diet or exercise, or determine a personal target. Children and teens, pregnancy or postpartum, edema or fluid shifts, eating-disorder care, and clinical decisions need individual professional interpretation.
Sources and method
- US NTIS — 1999 Naval Health Research Center circumference report metadata
- National Academies — historical circumference equations and standard errors
- Singapore Medical Journal — published metric equation coefficients
- US Navy — February 2025 historical BCA tape-location training
- National Academies — limits of circumference prediction
- MyNavy HR — current Physical Readiness program materials