While taking feet measurement intended for skating shoes, it will be a no-brainer not to wear the particular sock you will put on while skating. So with the sock put on snugly, stand with your back against the wall and the heels should touch the foot of the wall. And stand on a paper that has its end attaching the wall.
Now mark both ends of your feet with pencil and then take a measurement of your feet. Thus how you can come out with the actual feet size for skating.