How to measure...anything. Part 1

You're standing in the aisle at the big box home store, your wife is guarding a pallet of whatever is on clearance today.  How many do you need?  Do you buy the whole pallet?  Is the pallet enough?  Remember the last time? You trucked the whole thing home and went for it. And ran out of the stuff about a foot short of the back wall.  That was last year and you still can't find that same style/color/pattern.  And for some reason, you think today will be different.