Relative fat mass (RFM) estimates your body fat percentage from just your height and waist size. Enter both, pick your sex, and see your RFM, its category, the obesity cutoff and how it compares with your BMI.
Last updated:
Units
Sex
cm
cm
At the navel / midway between lowest rib and hip bone, after breathing out
ft
in
in
Measured standing, after breathing out normally
Optional: compare with BMI
Enter your values to see the result.
Advertisement
Advertisement
How to use the Relative Fat Mass Calculator
Choose units: metric or US (feet and inches).
Select your sex, since the formula adds 12 points for women.
Measure your waist standing, tape level, after breathing out normally.
Enter your height and waist, plus your weight if you want a BMI comparison.
Read your RFM, its category and the waist size at the obesity cutoff.
How relative fat mass is calculated
RFM turns the ratio of height to waist into a body fat percentage. A larger waist for the same height lowers the height-to-waist ratio and raises the estimate.
Men: RFM = 64 − 20 × (height ÷ waist)
Women: RFM = 76 − 20 × (height ÷ waist)
Example: a man 175 cm tall with an 88 cm waist has a ratio of 175 ÷ 88 = 1.989, so RFM = 64 − 39.8 = 24.2%. A woman 163 cm tall with an 80 cm waist gets 76 − 20 × 2.0375 = 35.3%.
RFM categories used here
Category
Men
Women
Essential fat
2–5%
10–13%
Athletic
6–13%
14–20%
Fitness
14–17%
21–24%
Average
18–24%
25–31%
Above average
25–29%
32–39%
Obesity range (RFM study cutoff)
30% or more
40% or more
The lower bands follow widely used body fat percentage charts; the obesity line is the cutoff proposed in the 2018 RFM study. Use the result as a screening estimate, not a diagnosis.
Waist size at the obesity cutoff
Rearranging the formula gives the waist at which RFM reaches the cutoff: men: waist = height × 20 ÷ 34 (about 59% of height); women: waist = height × 20 ÷ 36 (about 56% of height).
Height
Men (RFM 30%)
Women (RFM 40%)
155 cm (5 ft 1 in)
91 cm (35.9 in)
86 cm (33.9 in)
165 cm (5 ft 5 in)
97 cm (38.2 in)
92 cm (36.1 in)
175 cm (5 ft 9 in)
103 cm (40.5 in)
97 cm (38.3 in)
185 cm (6 ft 1 in)
109 cm (42.8 in)
103 cm (40.5 in)
Tips: measure on bare skin in the morning, take two readings and use the average, and track the trend over weeks rather than a single number.
Frequently asked questions
What is relative fat mass (RFM)?
RFM is a simple body fat estimate published by Orison Woolcott and Richard Bergman in 2018 (Scientific Reports). It uses only height, waist circumference and sex, and was checked against DXA body fat scans from the US NHANES survey.
What is the RFM formula?
For men: RFM = 64 − 20 × (height ÷ waist). For women: RFM = 76 − 20 × (height ÷ waist). Height and waist must be in the same unit. The single formula is 64 − 20 × height/waist + 12 × sex, with sex = 1 for women and 0 for men.
What RFM counts as obesity?
The study proposed RFM cutoffs of 30% or more for men and 40% or more for women to identify obesity, matching body fat thresholds measured by DXA. Below that, this calculator uses common body fat bands (athletic, fitness, average) for context.
Is RFM more accurate than BMI?
In the original study RFM matched DXA body fat better than BMI and misclassified fewer people as obese or not obese. BMI cannot tell muscle from fat, while RFM reflects fat around the waist. Neither is as accurate as a body composition scan.
Where should I measure my waist for RFM?
The study used waist circumference measured at the top of the hip bone (iliac crest) area, which is close to navel height for most people. Stand relaxed, keep the tape level and snug, and measure after a normal breath out.
Does RFM work for children or athletes?
RFM was developed for adults aged 20 and over. It is not meant for children, and it may be less accurate in pregnancy, in very muscular athletes or in people with unusual body shapes. A separate version for teenagers has been studied.
Why do women get a higher RFM for the same waist?
Women naturally carry more essential body fat than men. The formula adds 12 percentage points for women so that the result reflects that real difference at the same height-to-waist ratio.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.