To measure A and B, use a ruler. It is preferable to measure the foot over a thin sock.
Measure your size
Standing up straight, trace the footprint on a piece of paper. Measure from the middle of the heel A to big toe end point B (this can change according to the morphology of the foot).
Select right size
Now you have size in inches or cm, use Memo size conversion chart to determine what size you need. We recommend to measure both feet. Select size of shoes no less than additional 0.4'' (1 cm) and no more than additional 0.6'' (1.5 cm) to your size now.