Sit with your foot firmly on the floor, and your leg bent slightly forward so that your shin is slightly in front of your ankle.
Trace the outline of your foot and remember to measure your foot without shoes, but with socks similar to the ones you’ll be wearing with the shoes you are buying.
Hold the pencil or pen upright and perpendicular to the paper. Do not hold it at an angle. Make sure the pencil is resting snugly against your foot as you draw around it.
You may actually find it helpful to have someone else trace your foot. But as you can see in this image, it can be done alone.