I have photoshopped a to scale comparison of the 10.5 iPad pro vs the 12.9 iPad pro to get an idea of screen size.
Source for size:
Ipad 10.5 - https://www.piliapp.com/actual-size/ipad-pro-10.5/
Ipad 12.9 - https://www.piliapp.com/actual-size/ipad-pro/
Source for size:
Ipad 10.5 - https://www.piliapp.com/actual-size/ipad-pro-10.5/
Ipad 12.9 - https://www.piliapp.com/actual-size/ipad-pro/