Measure the Cobb angle on an X-ray
Mark the endplates of the upper and lower end vertebrae of the curve on the image, or enter their tilt angles; the angle between the two lines is the Cobb angle.
Use a standing posteroanterior spine radiograph. The image is processed in your browser; it is never sent to a server.
Cobb angle
Complete both lines or enter both tilts.
Method: Cobb JR. Outline for the study of scoliosis. AAOS Instructional Course Lectures, 1948. Definition threshold (≥10°): Scoliosis Research Society.
Not a diagnostic tool
Inter-observer differences of a few degrees are normal in Cobb measurement, and photos taken at an angle can change the result. Assessment and treatment decisions belong to the physician.
Who are you?
Run this measurement automatically from a scan in your clinic
In a 30-minute demo we'll show the same calculation on a 3D scan, with your own case. Your result is added to the form automatically.
Result added to the form
No calculated result yet — you can still send the form.
Frequently asked questions
What is the Cobb angle?
The Cobb angle is the standard method for quantifying spinal curvature (Cobb, 1948). It is the angle between lines drawn along the upper endplate of the most tilted upper vertebra and the lower endplate of the most tilted lower vertebra of the curve. The Scoliosis Research Society recognises it as the standard measurement.
At what angle does scoliosis start?
By the widely accepted definition, scoliosis is a Cobb angle of 10° or more on a standing posteroanterior spine radiograph. Treatment decisions depend not only on the angle but on age, skeletal maturity and the risk of progression, and are made by the physician.
Is a phone photo of an X-ray reliable?
If the photo is taken at an angle the image is distorted and the angle can change. Measure on the original digital image (exported from DICOM) where possible. Inter-observer differences of a few degrees are well known in Cobb measurement; this tool does not diagnose.
Which vertebrae should I mark?
Above and below the apex of the curve, choose the vertebrae most tilted from the horizontal (the end vertebrae). Draw one line along the upper endplate of the upper end vertebra and one along the lower endplate of the lower end vertebra. The tool gives the angle between the two lines.