After using a ruler or Brannock device to measure your foot, take your measurement in inches or centimeters. Compare the measurement to those on a chart to find your size in various countries, depending on the chart.
Before measuring, make sure you are standing on a hard surface and wearing the stockings or socks you normally wear with the type of shoe you are buying. If you are measuring at home, tape a piece of paper to the floor and draw an outline of your foot. Once that is done, take a ruler and measure your foot outline from heel to big toe. Compare this length to that of any manufacturer's size chart to find out which size you are.
If measuring at a store, you may ask for guidance in using a Brannock device. An employee should take your heel and line it up with the back of the device while you stand with both feet under equal weight. They may also press the foot down before taking the length to ensure finding your foot's longest possible length, and they use either a measurement from heel to toe or from heel to ball. Brannock devices are also helpful for determining an accurate width of the foot, as it also has a movable width measurement mechanism. The employee then takes the measurement and compares it to the chart they have to provide you with your size.