How is RFM calculated?

The RFM equations are straightforward: For Men: RFM = 64 - 20 * (Height / Waist). For Women: RFM = 76 - 20 * (Height / Waist). All measurements must be in the same units (e.g., centimetres or inches).

Why is RFM used alongside BMI?

BMI uses height and weight, while RFM uses height and waist circumference. Each metric has different uses and limitations, so RFM should be treated as an additional estimate rather than a universal replacement for BMI.

What is a healthy body fat range under RFM?

The calculator displays broad body-fat reference categories. These ranges are educational context only and should not be used to diagnose obesity or individual health risk.

Relative Fat Mass Calculator: RFM Body Fat Estimator

Relative Fat Mass uses height and waist circumference to estimate body-fat percentage. It provides different information from BMI, but it remains an estimate and its accuracy can vary between individuals and populations.

Calculate Your RFM

Enter your height and waist circumference to estimate your body fat percentage.

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The Science of the Relative Fat Mass (RFM) Index

1. A Simple Waist-Based Estimate

Laboratory body-composition methods such as DXA, hydrostatic weighing and air displacement plethysmography require specialist equipment. RFM was proposed as a simpler estimate that uses waist circumference, height and sex instead of body weight. It is useful for context, but it is not a direct body-composition measurement.

2. Mathematical Formulations

The RFM equations use height and waist in the same unit:

Male Formula:
RFM (%) = 64 - 20 × (Height / Waist)

Female Formula:
RFM (%) = 76 - 20 × (Height / Waist)

3. Validation and Limits

The original Scientific Reports study compared RFM estimates with DXA-derived body-fat data in research datasets. That does not make RFM equal to DXA or accurate for every person. RFM and BMI are both non-invasive estimates with different limitations.

Body Fat Percentage Classifications (RFM)

Compare your estimated RFM score to standard demographic body fat classifications:

Classification	Male Range	Female Range	Interpretation
Athletic / Lean	6.0% - 13.9%	14.0% - 20.9%	Broad fitness reference category.
Fitness / Fit	14.0% - 17.9%	21.0% - 24.9%	Broad fitness reference category.
Average / Acceptable	18.0% - 24.9%	25.0% - 31.9%	Educational reference category, not a diagnosis.
High / Obesity Range	25.0% or higher	32.0% or higher	Higher body-fat estimate; confirm with broader context if concerned.

How the Calculation Works

Asterisks Fit RFM estimates use the published RFM equations:

Woolcott & Bergman (Scientific Reports, 2018): Introduced RFM as a height-to-waist estimator of whole-body fat percentage and compared it with DXA-derived data in study populations.

Formula based on the published equation. Methodology reviewed by the Asterisks editorial team. Last content review: June 2025.

Last Updated: June 2026

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Frequently Asked Questions

Disclaimer: RFM body-fat percentages are statistical estimates. Muscular structure, genetics, measurement technique and population differences can influence accuracy. Full disclaimer →