Measure while standing with your foot firmly on the floor and parallel to your other foot. 
Preferably in the afternoon (Not in the night as the foot tends to be swollen at this time and not in the morning as the foot tends to be too thin at this time of the day)
After you have measured your feet if in doubt please send us the measurement of A and B and the length of your foot and we will help you select the correct shoe size for your preferred pair.
We do this to guarantee that our shoes fit you correctly as every shoes is made on a different last.