Relative Fat Mass (RFM) Calculator

Relative Fat Mass (RFM) Calculator for Endocrinology. The number estimates body-fat percentage within a model developed and validated in US adult survey data. It is not a DXA result, proof of metabolic health or a universal obesity threshold. A change in waist alone changes the result even when weight is unchanged.

For shared guidance on choosing a tool and documenting results, read the clinical calculator workflow.

How this calculator works

Relative fat mass is 64 - 20 x height/waist, with 12 added for the female coefficient. Because height and waist form a ratio, their units cancel only when they match. This implementation uses RFM, not the earlier Navy-method calculation.

When to use this calculator

Explore the RFM estimate from a consistently measured adult waist and height. Use the measurement protocol of the source study. On repeat visits, record who measured the waist and use the same anatomical site rather than changing the protocol.

Inputs used

  • Adult height and waist circumference in the same length units
  • Published male or female coefficient

Clinical interpretation

The number estimates body-fat percentage within a model developed and validated in US adult survey data. It is not a DXA result, proof of metabolic health or a universal obesity threshold. A change in waist alone changes the result even when weight is unchanged.

Worked example

At height 180 cm and waist 90 cm, height/waist is 2.0. The male-coefficient result is 24%; the female-coefficient result is 36%. Entering height as 1.8 while leaving waist as 90 would invalidate the calculation.

Limitations and safety notes

Measurement error, population differences, pregnancy and unusual body composition can undermine interpretation. Values outside 0-100% are rejected rather than converted into a plausible-looking zero. No athletic, fitness or disease categories are assigned.

Frequently asked questions

Why does Body Fat Calculator now say RFM?

The generic page now explicitly uses the source-checked RFM equation. It does not claim to implement a military assessment protocol. Compare previous results only after confirming their method.

References

  • https://pubmed.ncbi.nlm.nih.gov/30030479/

Editorial review and citation methodology

Maintained by the Quick Medical Calculator Editorial Team. Content record date: September 9, 2026. A content date is not evidence of independent clinical review. Individual clinical sign-off is not recorded on this page.

  • Prefer original validation studies for scoring systems and prediction tools.
  • Use current specialty society guidance, transplant allocation policy, public health guidance, or regulator resources when they govern clinical use.
  • Include limitations and safety notes when a calculator is population-specific, context-dependent, or unsuitable as a standalone decision tool.

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