Locate wooden letters in the wood cutout section of your local craft store. Measure the width of the letter at its widest point with a measuring tape. Divide the measurement by two. Use the measuring tape to mark the back of the letter at that measurement. In the case of letters where the center is in a hole, use the same method but measure on the upper arch. For example, for an O, use the upper arch of the O.
Place the measuring tape along the height of the letter. Set it so it crosses over the mark you made in Step 1. Draw a line down the height of the letter, using the measuring tape to keep the line straight. Record the height of the letter.
Divide the measurement from Step 2 in half. Mark the measurement on the straight line you drew to indicate the center of the letter.