Sometimes two stamps look alike and the only difference is the gauge of the perforations. Perforations are small rows of holes punched between stamps to make them easier to separate. We use a perforation gauge to measure the number of holes or teeth within two centimeters. If a stamp has 11 perforations in 2 cm, we say its “Perf 11.” Here are some tips to get a precise measurement.To measure your stamp, lay it on the center
of your gauge. Slide the stamp up or down until the perforations on the stamp line up exactly with the pattern on the gauge.
Be sure to measure horizontally and vertically, because many stamps have different sized perfs. These stamps will be listed with the horizontal perforations first, then the vertical. (For example, the 1984 Winter Olympic stamps, U.S. #2067-70, measure perf 10 ½ X 11. That means there are 10 ½ perfs every 2 cm horizontally and 11 perfs every 2 cm vertically.)