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Your Relative Fat Mass from two measurements.

RFM estimates body fat percentage from just two measurements — height and waist — making it one of the simplest body composition tools with no equipment needed.

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RFM — Relative Fat Mass
Body fat % from height and waist only — no calipers needed
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Your data

in
in
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Your result

— %
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Enter your measurements above
Height / Waist ratio—
RFM estimated body fat %—
Category—

How it's calculated

One ratio, two measurements, no equipment

The RFM (Relative Fat Mass) calculator estimates body fat percentage from height and waist circumference using the formula published by Woolcott & Bergman (2018). For a man 175 cm tall with a 84 cm waist, RFM ≈ 22.4% (average category). For a woman 165 cm tall with a 78 cm waist, RFM ≈ 27.1% (average category).

The formula was developed to outperform BMI in predicting body fat measured by DEXA scan. Unlike BMI — which uses weight without distinguishing muscle from fat — RFM uses waist circumference, which directly reflects abdominal adiposity. Both measurements must be in the same unit; internally we convert to centimetres.

RFM (men) = 64 − (20 × height ÷ waist)
RFM (women) = 76 − (20 × height ÷ waist)
  1. 1
    Convert inputs to centimetres (if entering inches)
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  2. 2
    Calculate the height ÷ waist ratio
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  3. 3
    Apply the sex-specific constant to get body fat %
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  4. 4
    Map result to body fat category
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Understand the terms

RFM (Relative Fat Mass)
A body fat estimator using only height and waist. Published by Woolcott & Bergman (2018). Correlates more strongly with DEXA-measured fat than BMI.
Height/Waist ratio
The core input to RFM. A higher ratio (tall and slim) yields lower estimated body fat; a lower ratio (short or wide waist) yields higher fat.
DEXA
Dual-energy X-ray absorptiometry — the gold standard for body composition. RFM was validated against DEXA in thousands of subjects.
Essential fat
The minimum body fat required for normal physiological function. Falling below this level risks organ damage and hormonal disruption.
See the full glossary →

🔢 Worked example

Man of 1.75 m with an 85 cm waist: RFM = 64 − 20 × (175 ÷ 85) ≈ 23% body fat.

Disclaimer: estimation tool for informational and planning purposes, using the Woolcott & Bergman (2018) formula. RFM is an estimate — actual body fat varies by measurement technique and individual body composition. Does not account for muscle mass, ethnicity or age variations. It does not replace assessment by a physician, dietitian or sports scientist.

Frequently asked questions — RFM

What is RFM (Relative Fat Mass)?
RFM is a body fat percentage estimator developed by Woolcott & Bergman (2018) that uses only height and waist circumference. Studies show it correlates more strongly with DEXA-measured body fat than BMI does.
How is RFM calculated?
The formula is: RFM = 64 − (20 × height ÷ waist) for men, and 76 − (20 × height ÷ waist) for women. Height and waist must be in the same unit. The result is the estimated body fat percentage.
What is a healthy RFM value?
Men: essential <5%, athletes 6–13%, fitness 14–17%, average 18–24%, obese ≥25%. Women: essential <12%, athletes 14–20%, fitness 21–24%, average 25–31%, obese ≥32%.
Is RFM more accurate than BMI?
Studies show RFM correlates more strongly with DEXA-measured body fat than BMI. BMI uses weight and can't distinguish muscle from fat. RFM uses waist circumference, which directly reflects abdominal adiposity — a more meaningful health marker.
Where should I measure my waist for RFM?
Measure at the navel (belly button) level, tape horizontal and snug but not compressing the skin. Exhale normally before measuring. Do not hold your breath or suck in your stomach. Record to the nearest 0.5 cm or 0.25 in.
Are my results saved? Do I need an account?
No account or sign-up needed. Every calculation is saved automatically in your own browser, and you can also pin a result with the save button. Nothing is sent to any server: the data stays on your device and can be erased at any time with the clear button.
How do I track my progress over time?
From the fourth entry onward a “View comparison chart” button appears, opening a line chart with every entry in time order plus an indicator panel: total change, average per entry, lowest and highest value and the period covered. You can also export the history as CSV.

📚 Learn more — official sources

🔬 Study Woolcott & Bergman (2018) — Relative Fat Mass (RFM) as a new estimator Original study proposing RFM as a better surrogate for body fat percentage than BMI, validated against DEXA in a large US cohort. See on PubMed → 🏛️ Organization NIH — Assessing body composition National Heart, Lung, and Blood Institute reference on body weight and composition assessment methods for clinicians and patients. See official source → 🏛️ Organization WHO — Waist circumference and waist-hip ratio World Health Organization report on waist circumference as a direct indicator of abdominal obesity and associated health risks. See official source → 🔬 Study Bergman et al. (2011) — Relative fat mass — background Background research establishing the theoretical and empirical basis for the RFM concept prior to the 2018 formula publication. See on PubMed →

🔄 Page last reviewed: July 2026. Laws and standards cited keep their original publication year; the date above is when the content and the calculation were reviewed.

About the RFM Calculator

The Relative Fat Mass (RFM) formula was published by Woolcott & Bergman in 2018 as a simpler, more accurate alternative to BMI for estimating body fat percentage. Unlike BMI, RFM uses waist circumference — which captures abdominal fat directly — making it a better predictor of metabolic health risks validated against thousands of DEXA measurements.

This calculator computes your RFM instantly with just two measurements and plots the result on a gauge with standard body fat categories. For a complete body composition picture, consider pairing RFM with the Navy method, FFMI or caliper skinfold measurements.

By Vinicius Fonseca · Formulas checked against scientific sources · Updated Jul 2026 · How we calculate →