"Diagonal measurement" refers to the length or distance across a shape or object from one corner to another corner that are not directly next to each other. Full definition
The new one measures 7.5 by 4.8 by 0.3 inches, yet the screen has the same six - inch diagonal measurements as always. (nytimes.com)
The two might share the same diagonal measurement, but in terms of area, the S8's screen would be smaller. (theverge.com)
The 6.2 - inch diagonal measurement of the S8 Plus is a little beguiling, as the phone's elongated shape breaks our usual method for comparing screen sizes across brands and models. (theverge.com)