Measure only the visible screen area, not the bezel or frame
Use a tape measure or ruler
Measure diagonally from one corner of the screen to the opposite corner
Start at the top-left corner and end at the bottom-right corner, or vice versa
Record the measurement in inches
Do not include the outer casing in the measurement
If needed, measure the screen width and height separately for reference
Compare the diagonal measurement to the monitor’s listed size