Is RFM more accurate than BMI?

Several studies suggest that RFM correlates better with body fat percentage measured by DXA scans than BMI does, especially across different ages and body types. However, like any simple index, it is still an estimate and can be affected by measurement errors or unusual body proportions.

Which units should I use for RFM?

You can use either metric (centimeters, meters) or imperial (inches, feet) units, as long as height and waist are in the same unit system. The RFM formula uses a ratio of height to waist, so the units cancel out.

Where should I measure my waist for RFM?

For RFM, waist circumference is typically measured at the level of the navel (belly button), with the tape horizontal around the body, after a normal exhale. Do not suck in your stomach or pull the tape too tight.

Can RFM be used for children or athletes?

RFM was developed for adults and is best interpreted in that context. For children, growth charts and pediatric BMI percentiles are usually preferred. For elite athletes with very high muscle mass, any simple index (BMI, RFM, waist-based formulas) may misclassify body fat, so more direct methods like skinfolds or DXA are recommended.

Relative Fat Mass (RFM) Calculator

Q: What is Relative Fat Mass (RFM)?

Relative Fat Mass (RFM) is an estimate of body fat percentage based on height and waist circumference. It was proposed as a simpler and often more accurate alternative to BMI because it uses a direct body measurement (waist) that reflects fat distribution.

Estimate your body fat percentage using the Relative Fat Mass (RFM) formula based on height and waist circumference.

RFM Calculator

Unit system

Sex

Male Female

Height

Waist circumference

What is Relative Fat Mass (RFM)?

Relative Fat Mass (RFM) is a simple index that estimates your body fat percentage using only your height and waist circumference. It was proposed as an alternative to Body Mass Index (BMI), because waist size better reflects how much fat you carry around your abdomen.

RFM uses different formulas for men and women and has been shown in research to correlate well with body fat measured by DXA (dual-energy X-ray absorptiometry).

RFM formulas

RFM is calculated from the ratio of your height to your waist circumference:

For men:

\(\text{RFM}_{male} = 64 - 20 \times \dfrac{\text{height}}{\text{waist}}\)

For women:

\(\text{RFM}_{female} = 76 - 20 \times \dfrac{\text{height}}{\text{waist}}\)

Important: height and waist must be in the same units (both in cm, or both in inches, etc.). The units cancel out in the ratio.

Example calculation

Suppose a man is 180 cm tall with a 90 cm waist:

\(\dfrac{\text{height}}{\text{waist}} = \dfrac{180}{90} = 2.0\)

\(\text{RFM} = 64 - 20 \times 2.0 = 64 - 40 = 24\%\)

How to measure your waist correctly

Stand upright, feet shoulder-width apart, relaxed.
Find the level of your navel (belly button).
Wrap a flexible tape measure horizontally around your waist at this level.
Exhale normally (do not suck in your stomach).
Make sure the tape is snug but not compressing the skin.
Record the measurement to the nearest 0.5 cm or 0.25 inch.

Interpreting your RFM result

There is no single universal cut-off for RFM, but the ranges below are commonly used for adults. Our calculator uses these to give you a qualitative category.

Suggested RFM ranges for men

Category	RFM (men)	Comment
Low / very lean	< 8%	Typical of competitive athletes; may be too low for some people.
Healthy range	8–20%	Common target range for general health.
High	20–25%	Increased risk of metabolic and cardiovascular issues.
Very high	> 25%	Obesity range; talk with a health professional about weight management.

Suggested RFM ranges for women

Category	RFM (women)	Comment
Low / very lean	< 18%	Typical of athletes; too low can affect hormones and fertility.
Healthy range	18–30%	Common target range for general health.
High	30–35%	Increased risk of metabolic and cardiovascular issues.
Very high	> 35%	Obesity range; consider medical advice and lifestyle changes.

RFM vs BMI

BMI uses only height and weight; it does not distinguish between fat and muscle.
RFM uses waist circumference, which reflects abdominal fat and fat distribution.
RFM can better identify people with normal BMI but high waist fat (so‑called “normal weight obesity”).
Both are screening tools, not diagnostic tests.

Limitations of RFM

It is an estimate, not a direct measurement of body fat.
Accuracy depends on correct waist measurement.
May be less accurate for very muscular individuals or those with unusual body proportions.
Developed for adults; not validated for children.

When to seek professional advice

If your RFM falls in the high or very high range, or if you have other risk factors (family history, high blood pressure, abnormal blood tests), consider speaking with a doctor or registered dietitian. They can perform more precise assessments and help you design a safe plan for weight and health management.