Method comparison
No average is used as a “consensus body fat.” Each method has different inputs and different population assumptions.
| Method | Body fat | vs headline | vs measured | Inputs |
|---|
OneFreePlace · Tool #140
Compare body-fat estimates instead of trusting one tape formula.
Run the legacy U.S. Navy circumference equation, Relative Fat Mass and the adult Deurenberg BMI-age-sex equation from one set of inputs. Then inspect fat mass, fat-free mass, target-body-fat scenarios, tape-measure sensitivity and optional comparison with a measured body-fat result.
✓ Navy circumference method✓ Relative Fat Mass
✓ Deurenberg adult equation✓ Measurement sensitivity
✓ Measured-result comparison
Body Fat Calculator
Navy · RFM · Deurenberg · composition · sensitivity
Inputs
Use consistent measurements from the same session.
Tape measurementsNeeded for Navy and RFM. Keep the tape level and snug without compressing tissue.
Male Navy equation: abdomen minus neck. RFM uses height-to-waist ratio. Use the same protocol every time if tracking change.
Primary resultComparison methods remain visible below.
Target-body-fat labAssumes fat-free mass stays unchanged—an accounting scenario, not a prediction.
Selected body-fat estimate
Calculating—
estimated body fat
Enter valid adult measurements.
Fat mass—weight × selected body-fat estimate
Fat-free mass—body weight minus estimated fat mass
Fat mass index—fat mass kg ÷ height²
Fat-free mass index—fat-free mass kg ÷ height²
Method spread—highest minus lowest of the 3 estimates
Waist / height—raw ratio used by RFM
Estimate, not measurementThree equations can disagree even when every measurement is entered correctly.
Composition from selected estimate
Fat mass and fat-free mass are derived from the selected percentage and current body weight. They are not separately measured tissues.
Tape-measure sensitivity
Small tape changes can move circumference-based estimates. Each row changes only one circumference by ±1 cm equivalent while holding everything else fixed.
| Scenario | Navy | RFM | Navy change | RFM change |
|---|
Target-body-fat scenario
This is a mass-balance thought experiment: if the estimated fat-free mass stayed exactly constant, what body weight would correspond to the selected target percentage?
Formula audit
The Navy equations use inches internally; metric entries are converted before the logarithms. RFM uses height and waist in the same unit. Deurenberg uses BMI, age and sex.
Measurement discipline
Repeat circumference readingsUse the same anatomical site, posture, tape tension and breathing phase. Repeating and averaging measurements can reduce operator noise.
ConsistencyDo not mix methods casuallyDXA, BIA, skinfolds and tape equations can have method-specific offsets. Trend with the same method when possible.
ComparabilityNo universal category verdictBody-fat cutoffs vary by sex, age, population, sport and source. This page reports estimates and method disagreement rather than assigning a universal health label.
Deliberatei
Adult estimation tool—not a body-composition scan.The Deurenberg adult equation reported a standard error of estimate around 4.1 percentage points in its original study, while the DoD circumference equations were also developed as prediction equations rather than direct measurements. Population differences, muscularity, hydration and measurement technique can all matter.