The US still uses the imperial system ... whereas the rest of the world has moved on :) and yes, 8.5 by 11 inches is US letter.
A4 is a tad larger and from memory the rest of the world follows the A system because it's easier to work with ... and remember ... even though some of us still think in inches and miles but work in decimals :)
And I still have half a box of tractor paper ... grandkids loved it when little and making long story drawings :)
@nygl Mandatory link to Matt Parker's video about paper sizes :D (no pun intended at all)
@nygl A4 when I'm printing on paper, but when I'm cardmaking I use letter size cardstock.
That's because some of US & Canadian cardmakers I follow on Patreon will share PDFs of printables that can be used in cardmaking (backgrounds, focal images, patterned paper, sentiments, etc), and the PDF files they produce are designed to be printed on letter size.
@nygl think anyone who isn't in the USA or Canada and who doesn't have tractor feed paper is A4.
They will learn hopefully :)
Kyna
Nigel Wadsworth
dan đź’ľ
Scott Small 🇨🇦
MyView
europlus 
Laurent
squelch41