Bone Density T-Score Calculator
Bone mineral density (BMD) measured by a DEXA scan is the standard method for diagnosing osteoporosis and assessing fracture risk. Your report will include a T-score, which compares your BMD to a healthy young adult reference, and a Z-score, which compares it to people your own age. The World Health Organization defines osteoporosis as a T-score at or below -2.5, and osteopenia (low bone mass) as a T-score between -1.0 and -2.5. This calculator takes your T-score (or Z-score) and classifies it according to WHO diagnostic criteria, explains what the result means for fracture risk, and outlines when further evaluation or treatment may be warranted. It also computes the estimated difference from peak BMD so you can understand the clinical significance of your result.
WHO T-score diagnostic criteria
T-score ≥ -1.0: Normal
-2.5 < T-score < -1.0: Osteopenia (low bone mass)
T-score ≤ -2.5: Osteoporosis
T-score ≤ -2.5 with fracture: Severe osteoporosis
Bone density: frequently asked questions
What is a T-score in bone density?
A T-score is the number of standard deviations your bone mineral density (BMD) is above or below the mean BMD of a healthy young adult reference population (peak bone mass). It is the primary diagnostic measure for osteoporosis, as defined by the World Health Organization.
What T-scores indicate osteoporosis?
WHO criteria: T-score of -1.0 and above = Normal; T-score between -1.0 and -2.5 = Osteopenia (low bone mass); T-score of -2.5 or below = Osteoporosis; T-score of -2.5 or below with a fragility fracture = Severe osteoporosis.
What is a Z-score in bone density?
A Z-score compares your BMD to the average for your age, sex, and ethnicity. It is used in premenopausal women, children, and men under 50. A Z-score below -2.0 is considered 'below the expected range for age' and may warrant further investigation.
How is bone density measured?
Dual-energy X-ray absorptiometry (DEXA or DXA) is the gold standard for measuring bone mineral density. It is a low-radiation imaging test that typically scans the lumbar spine and hip. Results are expressed as BMD in g/cm squared and as a T-score and Z-score.
Who should get a bone density scan?
The U.S. Preventive Services Task Force recommends screening for women aged 65 and older, and younger postmenopausal women with risk factors. Men are typically screened if they have risk factors (long-term corticosteroid use, low body weight, fracture history, hypogonadism).
Official sources
- World Health Organization: Osteoporosis Fact Sheet.
- National Osteoporosis Foundation: Bone Density Exam/Testing.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.