What is estimated
Adult body-fat percentage from height, waist circumference, and the published sex-specific term.
Relative Fat Mass Calculator
Estimated relative fat mass
Enter your values, then calculate to see a verified result.
Reference range
How this result is calculated
A clear calculation path based on your inputs.
Inputs usedReview the information used for this result.
Full calculation and sourcesReview the equation, normalized inputs, assumptions, and version.
Versioned calculationFormula v1.0.0
Method
The 2018 RFM equation uses height and waist in the same unit and does not use body weight.
Important boundary
RFM is a population-derived estimate. It is not DXA and has not been equally validated for every age, ethnicity, pregnancy state, or body type.
Normalize height and waistUse the same unit for both dimensions.
175 cm and 85 cmCalculate the ratio termMultiply height divided by waist by 20.
20 x 175 / 85Apply the equation termUse the published 0 or 12 coefficient term.
Male term 0; female term 12Interpretation
% is the equation-based adult body-fat estimate.
Waist measurement error carries directly into the result.
Use direct assessment when a clinical decision depends on body composition.
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Related calculators and resources
Method and test recordFormula v1.0.0
- Recorded scope
- health-body-composition
- Publisher
- CalculatorGeek
- Recorded review date
- 2026-10-04
- Next source review
- 2027-10-04
- Definition fixtures
- 4 configured scenarios
- Published examples
- 4 shown below
Recorded method
Independently evaluate the published equation, verify the sex-term branch, compare centimeter and inch parity, and reject combinations outside the supported geometry.
These records describe the published model and reference tests. A test-case count is not a certification of every possible input or an independent specialist review. Editorial policy
Known limitations
- RFM estimates, rather than measures, whole-body fat percentage.
- The derivation and validation populations do not represent every population or clinical condition.
- Measurement error in waist directly changes the estimate.
- Pregnancy, children, and conditions affecting abdominal size require different assessment.
Method sources
- Woolcott and Bergman (2018): Relative fat mass estimator
- External validation of RFM in adults from north-west Mexico
- CDC NHANES Anthropometry Procedures Manual
Latest model update
2026-10-04 - Initial CalculatorGeek shared-system implementation with source-backed method, fixtures, content, and result journey.
Reference inputs and expected results
Up to 12 examples from the configured definition fixtures are shown. Expected values use the stated output units; invalid inputs are intended to be rejected.
| Case | Inputs | Expected result |
|---|---|---|
| male reference | Equation sex term: male; Standing height: 175 cm; Waist circumference: 85 cm | Estimated body fat by RFM: 22.82352941 %; Waist-to-height ratio: 0.485714 (allowed numeric tolerance: 0.0001) |
| female coefficient route | Equation sex term: female; Standing height: 175 cm; Waist circumference: 85 cm | Estimated body fat by RFM: 34.82352941 % (allowed numeric tolerance: 0.0001) |
| imperial parity | Equation sex term: male; Standing height: 68.897638 in; Waist circumference: 33.464567 in | Estimated body fat by RFM: 22.8235 % (allowed numeric tolerance: 0.002) |
| invalid waist | Equation sex term: male; Standing height: 175 cm; Waist circumference: 20 cm | Reject invalid input: waist |
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What the Relative Fat Mass Calculator answers
Estimate adult body-fat percentage with the published RFM equation using height, waist, and the equation sex term.
The calculator shows the companion waist-to-height ratio and keeps population and measurement limitations beside the result.
Start with the Health calculators hub when you need to choose a different body-measurement method.
How to use the Relative Fat Mass Calculator
- Select the coefficient set used by the published equation.
- Measure standing height and waist circumference.
- Use the same unit for both measurements.
- Interpret RFM as a population-derived estimate rather than a direct fat measurement.
For a complementary body-measurement workflow, use the Body Roundness Index Calculator. Use the original ellipse-based waist-height geometry.
Formula, variables and method
RFM = 64 - (20 x height / waist) + (12 x sex term). The source equation uses 0 for the male coefficient set and 1 for the female coefficient set. Height and waist must use the same unit.
The calculator also reports waist-to-height ratio so the underlying dimension ratio remains visible.
To compare this method with a different input model, open the Waist-to-Hip Ratio Calculator. Compare waist with hip circumference.
Worked examples and boundary checks
175 cm height and 85 cm waist
For the male coefficient set, 64 - (20 x 175 / 85) = 22.82%, displayed as 22.8%.
Same dimensions, female coefficient set
The published equation adds 12 percentage points, producing 34.82%.
How to interpret the result
RFM is an equation estimate of whole-body fat percentage from anthropometry. A single value should not be treated as a diagnosis or a measured composition result.
- RFM estimates, rather than measures, whole-body fat percentage.
- The derivation and validation populations do not represent every population or clinical condition.
- Measurement error in waist directly changes the estimate.
- Pregnancy, children, and conditions affecting abdominal size require different assessment.
For another relevant cross-check, continue with the Body Fat Calculator. Compare a circumference-based body-fat method.
Frequently asked questions
Why does RFM not use body weight?
The published equation was selected from height-waist anthropometric combinations and does not include weight.
Do inches and centimeters give the same RFM?
Yes, when height and waist use the same unit.
Is RFM more accurate than BMI?
The derivation study reported better prediction of DXA body-fat percentage in its validation dataset, but that does not make RFM universally superior for every population or purpose.
Where should I measure waist?
Use one documented protocol and do not mix measurement sites between comparisons.
Can RFM replace DXA?
No. RFM is a regression estimate; DXA and other direct methods answer a different measurement question.
Primary sources and evidence limits
- Woolcott and Bergman (2018): Relative fat mass estimator
- External validation of RFM in adults from north-west Mexico
- CDC NHANES Anthropometry Procedures Manual
Sources were checked 2026-10-04. They establish the published method or measurement context; they do not turn an anthropometric estimate into a diagnosis, direct body-composition measurement, or treatment recommendation.