What size screen do I have

The screen size is 9.7 inches. Here are the technical specs for that model.

https://support.apple.com/kb/SP692?locale=en_US

The iPad Air1 has a 9.7” screen.

Screen size is measured diagonally - excluding the screen bezel - across the visible area of the screen.

It's a 9.7 inch diagonal screen.

9.7 inch diagonal. See: https://en.wikipedia.org/wiki/List_of_iOS_and_iPadOS_devices#Discontinued_and_unsupported_2