Knowing how to measure your insoles is vitally important when you buy insole inserts for your shoes, and also when purchasing vintage or used shoes online. Often, knowing your insole measurements -- and comparing them to those of shoes sold online -- is the only way of knowing whether shoes you can't try on will fit you. To properly measure your insoles for a good fit, you’re going to need to start with the pair of shoes you own that fit you best.

Slide the “zero” end of the tape measure carefully into your shoe. Use your fingers to feed it forward into the toe of the shoe until the edge of the tape measure meets the forward edge of the shoe.

Put the fingers of one hand as far into the toe of the shoe as possible to hold the end of the tape measure in place. Then carefully smooth the tape measure flat along the insole of the shoe, straight back toward the heel. Press the tape measure into the “corner” of the heel and read the number there. This is your insole length, and is also the inside shoe length of the shoe you’re measuring.

Grasp the “zero” end of the tape measure in one hand. Hold the tape measure at around the 6-inch mark with your other hand. Press the tape measure between your hands outward into a loop, and then slide this loop into the forward part of the shoe.

Use the thumbs on both hands to press the tape measure flat against the sides of the shoe. Stretch it evenly across the widest part of the shoe, then note the measurements at each edge. Subtract the smaller measurement from the larger to get the actual distance between them. This is your insole width and also the inside shoe width of the shoe you’re measuring.