Begin by finding out the length of your foot in cm (see the graphic below on how to do that), then calculate your European size, according to this formula:
SIZE = 1.5 X (FOOT LENGTH IN CM + 1.5)
That means, if your foot length is 28.5cm, you should add 1.5, to give you 30. Then multiply 30 by 1.5, to give you a European Shoe Size of 45 (assuming you don't have a very wide foot, in which case you might want to consider going up one size to 46).
For a more detailed breakdown, see our size guide page. Or email us (firstname.lastname@example.org) with any sizing questions you might have.