Body Fat Percentage Calculator
Body fat estimated four different ways — BMI-based, Navy tape, RFM and skinfold — so you can see how much they disagree.
Every field method is an estimate, and they do not agree.
How the body fat percentage calculator works
Every field method is an estimate, and they do not agree. The Deurenberg equation uses BMI, age and sex; the Navy method uses circumferences; relative fat mass uses only height and waist; the Jackson-Pollock skinfold method uses calipers.
Showing four together makes the uncertainty visible. If they cluster within a couple of points, the estimate is probably reasonable. If they spread over eight points, no single one deserves much weight.
Formula: RFM = 64 − (20 × height/waist) + (12 if female)
Worked examples
| Inputs | Average of the methods | Note |
|---|---|---|
| Male, 178 cm, 84 kg, 88 waist | 21.97% | the three methods land within a few points |
| Female | 31.1% | about 29% |
| Without a neck measurement | 23.6% | Navy is skipped; two methods remain |
FAQFrequently asked questions
Which method is most accurate?
None of them is good. Against DEXA, all field methods carry several points of error. Showing three at once makes that visible rather than hiding it.
What is relative fat mass?
A 2018 formula using only height and waist. It performed comparably to older equations against DEXA and needs just one tape measurement.
Why do the methods disagree?
Because each was fitted to a different population. Someone whose build is unlike that population will read differently on each.
How should I use this?
For tracking. Measure the same way each time and watch the trend; the absolute figure carries far more uncertainty than the change does.
What is a healthy body fat percentage?
Roughly 8 to 19% for men and 21 to 33% for women aged 20 to 39, rising modestly with age.
Where these figures come from
- Mifflin MD et al., "A new predictive equation for resting energy expenditure in healthy individuals", Am J Clin Nutr 1990 — the BMR equation used here
- World Health Organization — Waist circumference and waist–hip ratio (2008 expert consultation) — waist-to-hip cut-offs
- Tanaka H, Monahan KD, Seals DR, "Age-predicted maximal heart rate revisited", J Am Coll Cardiol 2001 — 208 − 0.7 × age
- Nathan DM et al., "Translating the A1C assay into estimated average glucose values" (ADAG), Diabetes Care 2008 — eAG = 28.7 × A1c − 46.7
- Mosteller RD, "Simplified calculation of body-surface area", N Engl J Med 1987 — BSA = √(height × weight / 3600)
- NHS — national health guidance
Last checked: September 2026. The equations are fixed by their published papers and do not change with tax years or regulations; the thresholds quoted in verdicts name the body that set them.