Body Adiposity Index (BAI) Calculator
Proposed by Bergman et al. in *Obesity* (2011), the Body Adiposity Index (BAI) estimates percent body fat from just two measurements — hip circumference and height — so it works when a scale is unavailable (travel, the elderly, bed-bound patients). Enter sex, age, height and hip and you immediately see the BAI value plus the underfat / healthy / overfat / obese band published in Figure 5 of the original paper, stratified by sex and age decade.
Enter an age (integer, 20–79), height 100–230 cm and hip circumference 50–200 cm.
Your BAI
24.9
Healthy
Body-fat category
< 21 Healthy
21–32 Overfat
33–38 Obese
≥ 39
Hip-to-height ratio sits in the normal range for your sex and age — keep up balanced eating and regular activity.
Reference cut-offs from Bergman et al. (2011). BAI ignores weight; pregnancy and pear-shaped builds can overstate body fat.
Formula
BAI = hip (cm) ÷ height (m)^1.5 − 18
- · Formula source: Bergman R.N. et al. (2011), "A Better Index of Body Adiposity", *Obesity* 19(5):1083–1089.
- · The healthy/overfat/obese cut-offs come from Figure 5 of the same paper, stratified by sex and age decade — values widely reproduced by Calculator.net, AccuMeasure, MDApp and others.
- · Hip circumference is measured around the widest part of the hips and buttocks; height is best measured against a wall to the nearest 0.5 cm.
- · BAI advantages: weight-independent, more stable across ethnic groups than BMI. Limitations: it under-reports body fat in very lean or muscular people and over-reports it in pregnancy and pear-shaped builds.
- · Reference population was African-American and Mexican-American adults; validation in East Asian populations is limited, so combine with waist-to-hip ratio or body-composition measurements for a fuller picture.
- · Valid age range is 20–79; adolescents (<20) and the very elderly (≥80) are not covered by the published bands.
Frequently asked
Is BAI more accurate than BMI?
It depends. Bergman's paper reported that BAI tracked DXA-measured body fat (the current gold standard) more closely than BMI, particularly in muscular individuals where BMI mis-classifies them as overweight. However, later studies (Freedman 2012, Schulze 2012) found BAI correlated *less* well than BMI with DXA in white men — especially those with central obesity. Practical advice: read BAI alongside BMI. When the two agree you can be confident; when they diverge, use waist-to-hip ratio (WHR) or waist-to-height ratio (WHtR) as a tiebreaker.
Why does age matter for the cut-offs?
Body composition shifts with age — muscle mass falls and fat mass rises (the so-called sarcopenic shift), so the same BAI value can be "high" at 30 yet "normal" at 65. Bergman's paper publishes separate cut-offs for ages 20–39, 40–59 and 60–79. For example, the male healthy ceiling is 21 at 20–39, 23 at 40–59 and 25 at 60–79. Age is required so the tool can pick the right row of the reference table.
I do not have a tape measure — any way to estimate hip circumference?
Use a non-stretch string or paper strip around the widest part of your hips, mark the overlap, then measure the distance with any ruler (a banknote, the 21 cm short edge of A4 paper, etc.). A cruder estimate: men's jean waist + 5–10 cm ≈ hip; women's low-rise pant waist label + 15–20 cm ≈ hip. But BAI is most sensitive to hip — the formula uses hip linearly, so a 10 cm error shifts BAI by ~4 units, which is enough to jump a category. A real measurement is strongly preferred.
Can I use BAI during pregnancy?
Not recommended. BAI assumes that hip circumference reflects hip-area body fat, but during pregnancy hip changes reflect the fetus, amniotic fluid, uterus and pelvic tissues — not fat. The same caveat applies the first 6–12 months postpartum, in the premenstrual week (water retention), or while recovering from hip injury/surgery. Use pregnancy-specific BMI gestational-weight-gain guidance (e.g. IOM 2009) or consult your obstetric team instead.
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