RFM calculator — body fat % from waist & height
RFM (Relative Fat Mass) estimates your body fat percentage from just two measurements: height and waist circumference. The formula is 64 − 20 × (height ÷ waist) for men and 76 − 20 × (height ÷ waist) for women (Woolcott & Bergman, 2018) — the same one the NOMS engine uses.
Reading your number — without judgement
Body fat exists on a wide, normal human spectrum, and essential fat is exactly that — essential. These reference ranges describe where a value typically falls; none of them is a grade:
| Range (men) | Range (women) | Typically seen in |
|---|---|---|
| 2–5% | 10–13% | Essential fat — the minimum the body needs to function |
| 6–13% | 14–20% | Competitive athletes at peak condition |
| 14–17% | 21–24% | Regularly training, visibly fit people |
| 18–24% | 25–31% | The broad healthy average — most people live here |
| 25%+ | 32%+ | Higher stores — a data point, not a verdict; trends matter more than snapshots |
What matters for your energy needs and your health is the trend over months — a single measurement is just a starting point.
The science behind the formula
- RFM was derived and validated by Woolcott & Bergman ("Relative fat mass as a new estimator of whole-body fat percentage", Scientific Reports, 2018) on ~12,000 adults, tracking DXA scans more closely than BMI.
- The NOMS engine clamps the estimate to a physiological 5–60% range and uses it to derive lean body mass: LBM = weight × (1 − body fat%).
- With lean body mass known, NOMS switches your resting-energy formula to Katch-McArdle (370 + 21.6 × LBM) — see the TDEE calculator.
Frequently asked questions
What is RFM and why not just use BMI?
RFM (Relative Fat Mass) estimates body fat percentage from height and waist circumference. Unlike BMI, it distinguishes where mass sits — a muscular person and a person with more abdominal fat can share a BMI but have very different RFM values.
How do I measure my waist correctly?
Measure at the top of the hip bone (iliac crest), roughly at navel level, after a normal exhale, with the tape snug but not compressing the skin. Same time of day gives the most comparable numbers.
How accurate is the RFM estimate?
In the validation study (Woolcott & Bergman, 2018, ~12,000 adults) RFM tracked DXA-measured body fat more closely than BMI. It is still an estimate — useful for tracking your own trend, not a lab measurement.
What does NOMS do with this number?
If you share your waist measurement, NOMS uses RFM to estimate lean body mass and switches your resting-energy formula to Katch-McArdle, which personalizes your calorie target. No number is ever used to judge you.
Track this daily in Telegram
Your body fat estimate personalizes your calorie target — and NOMS keeps score of the daily part: send a photo, a voice note or a text and get calories, protein, fat, carbs and fiber in seconds.
Track this daily in Telegram