check out the thread chart on the Superior Thread Co. website. But generally speaking, the higher the # with threads the finer it is. But there are 2 other factors with thread that go into the mix too--the # of plys (threads that are twisted) and wt--how "heavy' the thead is--so a #50 (SoFine) is a fairly fine, think it's a 2 ply thread. Superior MicroQuilter (a #100??)is finer still and I think it's also a 2 ply. Strength is usually higher with poly or poly coated with cotton threads.
Needles go the opposite direction--the higher the number the larger the needle. So a #16 is fine for jeans or heavy (4 layer) masks, but in quilting most will use a #11 or 12 quilting(fine point) needle. Many use a #14 Topstitch (a smidge longer) needle to quilt using their domestic machine.