Body Fat Calculator
What a tape measure can tell you that a scale cannot.
Relative Fat Mass needs your height and your waist, and nothing else. Across most groups it tracks measured body fat more closely than BMI does, and one measurement is the difference between a tool you finish and one you abandon.
Around the narrowest part of your middle, usually just above the navel. Stand relaxed and breathe out — do not pull it in.
Enter your measurements to see an estimate.
Interpretation
| Essential fat | 2 – 14% |
| Athletes | 14 – 21% |
| Fitness | 21 – 25% |
| Acceptable | 25 – 32% |
| Obese | ≥ 32% |
An estimate from a tape measure — not a body composition scan and not a medical diagnosis. Consult a healthcare professional for personal advice.
Why not just use BMI?
BMI cannot tell muscle from fat. It is weight against height, so a muscular athlete and someone carrying the same weight as fat get the same number — which is the single objection people raise about it, and it is a fair one.
A tape measure answers a different question. Waist circumference reflects the fat stored around the organs, which is the deposit most strongly linked to metabolic risk, and it is that measurement — not weight — that these formulas use.
The two methods
RFM — Relative Fat Mass needs your height and your waist, and nothing else. Across most groups it tracks measured body fat more closely than BMI does, and one measurement is the difference between a tool you finish and one you abandon.
US Navy — The US Navy circumference method adds your neck, and your hip if you are measuring as female. It is the more precise of the two, but a half-inch error on the waist moves the answer about a point, so measure carefully. It underestimates body fat in very lean people, such as athletes near contest weight.
What the bands mean
The categories come from the American Council on Exercise. Every band sits eight to ten points higher for women, because essential fat supports reproductive physiology — it is a difference in biology, not a courtesy adjustment.
ACSM publishes wider healthy ranges (10–22% for men, 20–32% for women) but agrees with ACE on where obesity begins. Where two respectable bodies differ by that much, the honest reading is that the boundary is a broad zone rather than a line.
What this will not tell you
Where the fat sits matters as much as how much there is, and a percentage cannot say. Nor can it distinguish the changes that come with age, or account for pregnancy, or replace a scan.
This calculator deliberately omits two things you will find elsewhere: a body fat figure derived from BMI, which is BMI rescaled and carries no new information, and a target telling you how much to lose. It reports what you measured and leaves the goal to you and your doctor.