I have heard expressions like "It was yay big" or "It was yay by yay." a couple of times now, always accompanied by a gesture indicating the size of something. Does anybody know where this word comes from? Can it be used in other situations? Is it older or newer than the word that? If it's of any help it is frequent in the UK.
Edit: I obviously tried searching for it myself but my results seem to be dominated by the word yay as an expression of joy. I assume the two are completely unrelated.