there no such standard as such. we have to accommodate the maximum with whatever is available.
but the widths which are suitable for few of them are..
toilet atleast 4'6" in width
kitchen atleast 5'6" in width and so on
for any clarification do post will reply for the same
In the Netherlands we've got building rules called: "bouwbesluit" you can find the english version here: Bouwbesluit (english)
but it might be hard to read through.