Why is the size of a character or block file given as comma separated?

crw-rw-rw-. 1 root root 1, 3 Mar  8 10:15 /dev/null

brw-rw----. 1 root disk 8, 1 Mar  8 10:15 /dev/sda1

Size of a file is the number of bytes occupied in the storage device. For character or block files what will be size? And can you please explain about its representation using comma?