We made a handy little print-out you can use to size yourself. All you'll need is access to a printer and a pair of scissors. Just click here to find the printout.
If you don't have a printer, you'll need a measuring tape.
If you don't have a measuring tape, the only suggestion we have is ordering a size up and resizing the Imperial if it's too large. The tips are easy to remove with a small screwdriver.