|I recently read that if you need to know the approximate yardage of fabric but don't have a tape measure handy, you can hold your fabric up to an exterior door. The book I read this in said a standard exterior door is 36" (1 yard, obviously). I just measured my door and it is 34", but I'd say that's a pretty good estimate for those of us who can't eyeball a yard.
Another method I use quite often: I'm completely dense and can't tell the difference between 45" and 60" widths. I'm 64" tall (5'4"), which means my armspan is 64". If I stretch the fabric nearly the width of my armspan, then it's 60" wide. If not, it's 45".