The best way to measure your feet is to do it in the afternoon. Your feet can swell during the course of the day which can impact the fit of your shoes.
Download and print the sizing charts on the "Resources" page. You can then use this as a guide to find your US/Canada size which is the most commonly used size on the world wide web shopping sites.
Another way is to measure your heal-toe length. Stand with one foot on a piece of paper and measure your heal-toe length. Mark the paper at the end of your heel bone. Mark the paper at the end of your longest toe. (Point A in photo above.) Measure the distance between these two points. Repeat this process for your other foot. If one foot is slightly larger than the other, use the larger as your foot size.
Be Careful With Conversions
While every care has been taken to compile these sizing charts from sources all over the world, many manufacturers use their own sizing standards that don't neccesarily adhere to international standards. As such you should exercise caution when purchasing online and request Modopoint / Millimeters, Centimeters or Inches sizes from sellers. These sizing standards are completely universal and can also be double-checked using your existing shoes and/or sizing checks from the download charts on the "Resources" page.
Modopoint - The International Standard
The International Standard is ISO 9407:1991, "Shoe sizes - Mondopoint system of sizing and marking", which recommends a shoe-size system known as Mondopoint. It is based on the mean foot length and width for which the shoe is suitable, measured in millimetres. A shoe size of 280/110 indicates a mean foot length of 280 millimetres (11 in) and width of 110 millimetres (4.3 in). Because Mondopoint also takes the foot width into account, it allows for better fitting than most other systems.