A4 and A5 are standard paper sizes in Europe, and most of the world, really. They're part of the ISO 216 standard.
A4 = 210 x 297 mm = 8.27" x 11.69"
A5 = 148 x 210 mm = 5.83" x 8.27"
Meanwhile, 8.5"x11" is the standard letter-paper size (and thus, copier/printer size) in the U.S., Canada and Mexico.
8.5" x 11" = 216 x 279 mm
Meaning, the standard A4 sheet in Britain/Europe is a little narrower and a little longer than the standard American sheet.
To be even more confusing... in the U.S. at least, paper intended for artists and sold in tablets is often sold in 9"x12" (229 x 305 mm) size, which is part of a standard used by architects and the entertainment industry.
See the Wikipedia page for
fun with comparative paper sizes.
These days, I tend to do my sketching on 9x12 paper, because I bought pads of art paper made for inking, which only comes in that size.
Peggy -- yeah, ideally, when I'm trying to do a sort of basic elf figure, I tend to make the figure nearly as big as the page I'm working on (the 9x12" paper; which will just fit on my scanner). When I do multi-figure pieces, I usually draw each figure (or sometimes pairs of figures) separately, and then put them together after I've inked and scanned them. (I think that this is a technique that has its flaws...) On occasion, I've tried to do a bunch of characters all on the same page, requiring each of them to be correspondingly smaller, and thus, lower on fine detail. The size of the figure affects how much detail I'll try to put into it, and what inking technique I'll use. (The calendar piece that I did for River Twine's calendar this year was a rare example of me drawing all of the figures together on the same page.)
Something for folks to think about, since I'm not sure it's widely known these days -- when you look at most comic books, I believe including ElfQuest, you have to realize that the artist usually draws the original page at a much larger size than the final printed comic book, and then the linework was photo-reduced for printing. I think I've read that comic artists do the originals on 11"x17" paper, or, typically twice the size of the finished product.
So if you are ever looking at a page of ElfQuest (pre-SATS), and you are thinking, "How did Wendy manage to do such tiny figures on the paper, with so much detail and such fine linework?" The answer is: she didn't, she originally drew them 2x that big.
If I had a scanner that could handle paper larger than 9x12, I'd probably draw bigger originals, too.