Mine is 3/4yd + 1/4yd put together...some other people make them a little bigger, but that size works just fine for me.
Here's a really neat tutorial for making them quick and easy...I wish I had made mine like this...it would have encased the seams. I'm going to make my next batch using this method.
Here's the link - it's on the bottom,right of the page...it's called the "roll'em up method"
http://www.allpeoplequilt.com/millionpillowcases/