Is Relative Fat Mass index (RFM) a better way to measure body fat?

June 28, 2022

While many methods exist to measure fat including skin-fold calipers and hydrostatic weighing, the Body Mass Index (BMI) has been the most common way to measure body fat content.

The challenge with BMI has been its inability to separate fat mass and non-fat mass. According to Cedars-Sinai healthcare professionals, BMI measurements misclassify about 60% of women and 13% of men when used to determine if someone falls into the "obese" category. So, the measurement has been anything but precise.

But that changed in 2018, when a more accurate way to measure how much body fat a person carries was developed through a study by researchers at Cedars-Sinai Diabetes and Obesity Research Institute.

Relative Fat Mass Index (RFM) means more accuracy

The study’s main authors Dr. Orison Woolcott and Dr. Richard Bergman named this new measurement for body fat simply the Relative Fat Mass Index, or RFM. The process is simple: you take your height and your waist circumference and plug them into a formula. The resulting number is roughly equal to your body fat percentage. Through their work, they discovered this formula was much more effective at predicting a person’s body fat percentage than the old BMI standard.

Two things to calculate your Relative Fat Mass (RFM)

One of the great advantages of using RFM to measure your body fat percentage is its simplicity. You need only two things:

  1. A simple tape measure, and
  2. A basic formula

The beauty of RFM is that it can be determined with nothing more sophisticated than a tape measure and some simple math.

First, grab a tape measure and note your height and your waist numbers. For best results, take the tape measure to just above the top of your hip bone and wrap it around your body. Just make sure your measuring numbers are consistent, e.g. inches/inches or centimeters/centimeters.

Then, after you’ve got your numbers, put them into the simple formula below:

  • Men: 64 – (20 x height/waist circumference) = RFM
  • Women: 76 – (20 x height/waist circumference) = RFM

For example, if you’re a 6’ man with 34-inch waist, your formula would look like this;

{64 – (20 x 72”/ 34” = 42) = 22} Relative Fat Mass

You can evaluate your result by looking at a standard developed by the American Council on Exercise below. However, it is always advisable to discuss your body fat ratio with your healthcare professional to ensure accuracy.

Body Fat Chart

How to keep your body fat at a healthy level

To keep your body fat ratio at a healthy level and free from diabetes and heart disease, you must take good care of yourself. This means practicing the time-tested combination of good nutrition and regular exercise. Of course, you should always consult with your healthcare provider before undertaking any diet or exercise program.

Eat the right kind of foods:

  • Maintain a regular diet of fresh vegetables and fruits
  • Choose whole grains and lean sources of protein
  • Drink water over sugary beverages
  • Eliminate or limit processed foods including snacks such as chips, cookies and candy
  • Keep an eye on your portion size

Maintain a daily exercise program of 30 minutes for most days:

  • Choose movement when possible throughout day; for example, take the stairs instead of an elevator when given the choice
  • Consider a brisk walk
  • Ride your bike or stationary bike
  • Work in your yard
  • Take a swim
  • Lift weights

To learn more about the best way to measure your relative fat mass index including a health check at home, talk to your health care professional.