Pillowcase measurements?

[Salsa]

I am making a pillowcase. I have measured a couple of my cases and they are 17" x 21. BUt I googled sizes of standard cases and everything I read came up bigger (and varied).
Anyone know?
ANyone want to measure their cases?

Im making a case that will probably be a bit bigger than standard size though, as its more a sort of feature pillow case I want to make.

[Trillian]

All I know is that there is standard and then European sizing, but I have no idea what the difference is and why pillows of all things come in different sizes ROFL.