'a squared' + 'b squared' = 'c squared'
Dimensions H x W x D, including base:
18.9 x 20.5 x 11.3 inches (48.1 x 52.3 x 28.9 cm)
The dimensions are in height x width x depth.
The 20.5 inches is the measure from left to right
The inches of a monitor are measured diagonally.
If you calculated the screen using pythagorus's theorum. You would come out with 22 inches.