Estimate adult body fat percentage from height, waist circumference, and sex using the Relative Fat Mass (RFM) equation. Switch units without changing the estimate and view measurement sensitivity.
Your measurements
Measure your waist consistently, with the tape level and not compressing the skin. Small placement differences can change the estimate.
Your estimate
Estimated relative fat mass
Male formula: 64 − 20 × (height ÷ waist)
| Height-to-waist ratio | 2.00 |
|---|---|
| If waist is 1 cm smaller | 23.5% |
| If waist is 1 cm larger | 24.5% |
The sensitivity values show how a 1 cm difference in waist measurement affects the result. This is an estimate, not a direct body-fat measurement.
How the RFM estimate works
Relative Fat Mass uses the ratio of height to waist circumference. Both measurements must use the same unit. The adult equation is 64 − 20 × (height ÷ waist) for males and 76 − 20 × (height ÷ waist) for females.
How to measure
- Stand upright and breathe normally.
- Use a flexible tape around the waist, keeping it horizontal.
- Record height and waist in the same unit, then calculate.
RFM was developed as a practical screening estimate and has been compared with DXA measurements in adult research. Accuracy can vary across individuals and populations, so use the result to understand a trend rather than as a diagnosis.
Frequently asked questions
Is RFM the same as BMI?
No. BMI uses weight and height, while RFM uses waist circumference and height. They answer different screening questions.
Can children use this calculator?
No. This calculator uses the adult RFM equation. Children and adolescents require age-specific assessment and different equations.
Why does waist measurement matter so much?
Waist circumference is the only changing body-size measurement in the equation, so tape placement and tension directly affect the estimate.
Is this a medical diagnosis?
No. It is an educational estimate. A clinician or qualified health professional can select an appropriate assessment method for medical decisions.
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Health disclaimer: This calculator provides a general educational estimate for non-pregnant adults. It does not diagnose body composition or health conditions. Seek professional guidance when measurements affect healthcare, nutrition, or training decisions.