Body fat calculator by RFM
Estimate body fat percentage with the RFM formula using height and waist, with estimated fat mass and lean mass.
Always use the same measuring spot to track the trend.
Used to estimate fat mass and lean mass.
Estimated body fat
22.3%
RFM estimate. Use it as a trend, not as a diagnosis.
Fat mass
16.7 kg
Derived from the estimated percentage.
Lean mass
58.3 kg
Total weight minus estimated fat mass.
Recommended use
trend
Repeat the measurement the same way over time.
RFM is a population-level estimate from measurements. Bioimpedance, calipers and professional assessment can tell another story.
Share
Terms used in this calculator
These concepts show up in the math and help you read the result with more context.
- RFM (relative fat mass)
- RFM estimates body fat percentage using the ratio between height and waist, adjusted by sex.
- Body fat percentage
- Body fat percentage estimates how much of your body weight comes from fat mass.
- Lean mass
- Lean mass is the body weight that is not fat, including muscle, water, bones, organs and other tissues.
RFM is an estimate from measurements
RFM uses the relationship between height and waist, adjusted by sex, to estimate body fat percentage. It's practical because it needs no calipers, bioimpedance or imaging.
Even so, it remains a population-level estimate. A poorly taken waist measurement, body type, fat distribution and individual context can shift the reading a lot.
Use it to track a trend
The best use is comparing measurements taken the same way over time, not treating a single result as absolute truth.
For training, also track strength, volume, adherence and recovery. The SelfShapeAI app works with that execution data, not body diagnosis.
Sources and references
- Source: Woolcott OO, Bergman RN. Relative fat mass (RFM) as a new estimator of whole-body fat percentage. Scientific Reports, 2018. — Scientific Reports
Reviewed by the SelfShapeAI research team.
Frequently asked questions
Is RFM more accurate than BMI?
It uses the waist on top of height, so it can capture more body-composition context than BMI. Even so, it's still an estimate, not a diagnosis.
Where do I measure the waist?
Use a tape without tightening it, at the waist, keeping the measurement consistent over time. Small differences in the spot change the result.
Does the calculator replace a physical assessment?
No. It's an educational tool. In-person assessments and clinical methods may be needed for individual decisions.
Keep reading
Take the math into your training
SelfShapeAI builds the plan, logs your loads and adjusts volume with context — so you don't have to run the numbers by hand.
