Most people find the 2nd toe the most comfortable. After getting these two numbers, find the middle size. Most people are between a size 2 - 4 . This way is a bit different, but will net the same results. You can use tape to hold one side down while you wrap the other side around.
Millimeters are the best and easiest choice, but inches work.
Once you have your measurement, use the chart below to figure out your size. All sizes are approximate. We know it's hard to get these exact measurement, so get as close as you can, don't worry to much about being perfect.