Use your ruler or measuring tape to measure the distance from the bottom line to the top line that you made on one of your foot tracings in step three.
Be sure to hold the measuring tape straight, and find the closest mark that you can on your ruler (for inches, use the closest 16th mark) - don't round up or down dramatically.
Write this number down, and repeat the process for the tracing of your other foot.
Now, you have the length of each of your feet, you'll need to also measure the width of your feet. (Next)