When you look at the face of a stamp, you'll notice the character is raised. The distance between the upper and lower raised ridges is known as the character height. This height is used to measure stamp size. If a stamp does not have a size marking on the shank, measure the character height to order the correct size.

The actual impression a stamp makes is larger than its character height and varies depending upon how hard you strike the stamp, the hardness of the material, and wear.