To determinate your shoe size, you should measure your foot from the back of your heel to the tip of you toe. the easiest way to do this is by drawing a straight line on a piece of paper and marking the end of your big tow and the end of your heel on the line, then measure the distance between the two marks. Do this for both feet, as they can often be different sized.
Size and fit may change depending on the model and shape.
Women’s shoe size chart