Bone Density T-Score Calculator (BMD to T-Score & WHO Category)

How it works

T-score = (your BMD − young-adult mean BMD) ÷ young-adult SD · reference (NHANES III, women 20–29, used by ISCD/FRAX for both sexes): femoral neck 0.858 ± 0.120 g/cm², total hip 0.942 ± 0.122 g/cm² · WHO: ≥ −1.0 normal; −1.0 to −2.5 low bone mass; ≤ −2.5 osteoporosis

A DXA scan measures bone mineral density in g/cm². The T-score expresses it as standard deviations above or below the average of healthy young adults: every 1.0 below the mean roughly doubles fracture risk. The World Health Organization defines osteoporosis as a T-score of −2.5 or lower at the hip or spine. For the hip, the International Society for Clinical Densitometry recommends the NHANES III white-female young-adult reference for everyone, which this calculator uses; spine references depend on the scanner maker, so choose "Custom" and copy the reference from your report. T-scores apply to postmenopausal women and men over 50; for younger people the Z-score (compared with your own age) is used.

Worked example

A femoral neck BMD of 0.700 g/cm²: (0.700 − 0.858) ÷ 0.120 = −1.32, so the T-score is -1.3 — low bone mass (osteopenia). That BMD is 82% of the young-adult mean; a T-score of −2.5 would correspond to 0.558 g/cm².

Sources: Looker AC, et al. Updated data on proximal femur bone mineral levels of US adults (NHANES III). Osteoporos Int 1998 · ISCD Official Positions — Adult · Bone Health & Osteoporosis Foundation: Bone density exam/testing

Frequently asked questions