To determine your shoe size, measure foot length (from the heel to the tip of the longest toe), foot width (widest part of the foot), and arch length.  “When sizing your shoes, for best accuracy, both feet should be measured while weight-bearing. Keep in mind that sizes may vary by brand or even among collections within the same brand," says podiatrist Elizabeth Bonarigo. If possible, measure your feet midday or early evening to capture natural foot swelling.