Health & Fitness Calculators
Body Fat Calculator
Estimate body fat percentage from defined circumference measurements with a historical equation.
Enter circumference measurements
Equation-set labels identify the historical source equations and measurement sites. They do not make a universal statement about sex or gender identity.
Select the source equation whose defined measurement sites you are using.
One inch equals exactly 2.54 centimetres.
Stand upright without shoes. Normalized range: 100 to 250 cm.
Measure horizontally just below the larynx without compressing tissue.
No estimate yet
Select an equation set and unit, enter the required measurements, then calculate.
What the estimate represents
The historical Hodgdon-Beckett method estimates body density from height and circumference measurements, then applies the Siri equation to estimate body fat percentage.
The male report studied U.S. Navy men aged 18 to 56. The female report studied U.S. Navy women aged 18 to 44. Results may be less reliable outside those source populations or at body-size extremes.
Why centimetre normalization matters
The body-density coefficients used here require centimetres. Inch inputs are multiplied by exactly 2.54 before any subtraction or base-10 logarithm.
No circumference, logarithm, density, or percentage is rounded until the final percentage is displayed to one decimal place.
Worked examples
Male equation: height 178 cm, abdomen 86 cm, and neck 38 cm gives an estimate of 17.2%.
Female equation: height 165 cm, natural waist 75 cm, neck 34 cm, and hip 100 cm gives an estimate of 28.9%.
These examples demonstrate the arithmetic, not expected or recommended results.
Limitations and common mistakes
- Mixing centimetres and inches or applying logarithms before unit conversion.
- Moving the tape site, compressing tissue, or changing posture between measurements.
- Treating a circumference equation as interchangeable with DXA, hydrostatic weighing, air-displacement plethysmography, or professional assessment.
- Reading the estimate as a diagnosis of health, nutritional status, obesity, or fitness.
Safety and trust
These results are population-based estimates, not direct body-composition measurements. Tape placement, posture, hydration, recent food intake, device accuracy, and measurement technique can affect results. They are not interchangeable with DXA, hydrostatic weighing, air-displacement plethysmography, or professional assessment, and do not diagnose health, nutritional status, obesity, or fitness.
Need estimated non-fat and fat mass from a body-fat percentage? Use the Lean Body Mass Calculator.
Quick answers
What this calculator answers
- Result: Estimates body fat percentage from height and defined circumference measurements.
- Equation: Uses the historical Hodgdon-Beckett body-density equations and the Siri conversion.
- Units: All accepted measurements are converted to centimetres before logarithms are applied.
- Limit: This is a population equation, not a direct body-composition measurement or the current Navy process.
- Related: Convert an entered body-fat percentage into estimated lean and fat mass. Lean Body Mass
Transparency note
Accuracy and limitations
Calzivo tools are built for practical estimates, conversions, and checks. Some tools use standard formulas or simplified assumptions, and results can be affected by input accuracy, rounding, units, local rules, or changing official requirements.
Health and fitness results are estimates, not medical advice. Formulas simplify real bodies and cycles, so important health decisions should be checked with a qualified clinician.
Reference check
Sources and references
These references provide background context for the topic. They do not replace official advice or documents for personal decisions.
- Prediction of Percent Body Fat for U.S. Navy Men from Body Circumferences and Height, Report 84-11
Naval Health Research Center
- Prediction of Percent Body Fat for U.S. Navy Women from Body Circumferences and Height, Report 84-29
Naval Health Research Center
- Body Composition in the Military Services: Standards and Methods
National Academies Press
- Guide-4: Body Composition Assessment
U.S. Navy Physical Readiness Program
How to Use This Tool
Use these steps to enter the right inputs and interpret the result correctly.
Select the male or female source equation set and a length unit.
Measure height, neck, and the equation-specific circumference sites.
Enter strict decimal tokens without spaces, signs, or unit text.
Calculate once and review the formula, substitution, and measurement reminder.
Repeat measurements at the same sites when comparing estimates over time.
Related Tools
Use the Lean Body Mass Calculator with an entered body-fat percentage, or compare the purpose of BMI.
Frequently Asked Questions
Common questions about Body Fat Calculator and how to read the result.
What does this body fat result represent?
It is a population-based estimate of body fat percentage from circumference measurements and height, not a direct measurement.
Why are there two equation sets?
The historical reports derived separate equations and measurement sites for male and female Navy samples. The labels identify those source equations and do not establish universal applicability.
Is this the current U.S. Navy assessment?
No. This calculator implements historical Hodgdon-Beckett circumference equations. Current Navy Guide-4 describes a different assessment process.
Why are measurements converted to centimetres?
The published body-density coefficients used here require centimetres. Converting before applying base-10 logarithms is part of the calculation.
How should the tape be positioned?
Keep it horizontal and snug without compressing tissue. Use the abdomen at the umbilicus for the male equation; use natural waist and widest hip for the female equation.
Is estimated body fat a diagnosis?
No. It does not diagnose health, nutritional status, obesity, fitness, or any medical condition.