> Do you print your letters on US Legal or something like that?
No, "letter size" was a reference to US Letter, which is 8.5"x11", which has a 13.9" diagonal, so a 14" screen would be about right (a little small for a 100% display if it is 3:2, because US Letter has a 1.29:1 aspect ratio rather than 1.5:1.)
US Legal is 8.5"x14" which is closer to 3:2 (1.65:1) but also 16.4" diagonal.