[nerdsniper]

Midwest, East Coast, and South I've seen some 1/2lb or 1lb blocks for fancier butters sometimes. But a pat of butter was definitely 1/4-1/2 tbsp of butter in the midwest - depending on if for toast (less) or for baking (exactly 1/2).

I've not heard "pat" used as a serious unit of volume since childhood though. In fact I rarely hear the word pat in relation to butter at all anymore.