"US Letter" is a horrible paper size - what is it with the U.S. and ridiculous measurements?
ISO 216 is the international standard (e.g. A4 size) and because they use an aspect ratio of the square root of 2, you can fold in half one size to get the next smaller size.
Thermal printers tend to be expensive as you use either special paper or special printing ribbons. They quite often create fumes which isn't pleasant and the prints tend to fade after a while, so not much good for archiving.
ISO 216 is the international standard (e.g. A4 size) and because they use an aspect ratio of the square root of 2, you can fold in half one size to get the next smaller size.
Thermal printers tend to be expensive as you use either special paper or special printing ribbons. They quite often create fumes which isn't pleasant and the prints tend to fade after a while, so not much good for archiving.