How to determine the right size?

Take a piece of paper and measure while standing the distance between the heel and the big toe. Add a size up if you hesitate. 

19: 11,5 - 12,0 cm

20: 12,1 - 12,6 cm

21: 12,7 - 13,2 cm

22: 13,3 - 13,8 cm

23: 13,9 - 14,4 cm