The following chart uses the Brannock standard to determine US footwear size. It should be noted that not all manufacturers strictly adhere to this standard, but this chart can give you an idea on what size you should be wearing. All measurements are given in Inches. You'll have to convert it to Metric yourself. If your feet measure smaller or larger than this chart supplies, use the raw measurement information to calculate your size.
This chart was painstakingly assembled by Crombie and is posted here with his permission. The Brannock Device is a measuring tool that you've seen in shoe stores and boot shops around the country.