How to Use a Perforation Gauge
by Kathleen Wunderly
Perforations, or perfs, are the holes added to sheets of stamps as part of the production process, so that users can separate the stamps easily. In some countries in the early days of stamp-issuing, stamps did not have perforations (imperforate stamps), and users had to cut or tear them apart.
The number of perforation holes, and the space between them, has varied a great deal across the world, over time. Stamp users care only about how difficult it is to tear stamps apart, but many stamp collectors want to know exactly what perforations are on which stamps. Why? Because measuring perfs is a form of identifying stamps, and because in some cases, the measurement of the perforations is what makes one stamp scarce, and another apparently identical stamp common. The design on the stamps may be the same, but the stamps may have been perforated in different gauges, with one variety much more difficult to find, and of greater value.
The bits of paper sticking out between the perf holes are called teeth. Do not count teeth in measuring. The size of the holes does not matter either. The standard of measure is the number of holes (perfs) in 2 centimeters. A stamp with 10 holes in every 2 centimeters is perf 10. Some stamps have a different measurement on the sides than they do on the top and bottom; these are called compound perfs, and the first number will be the top measurement - perf 11x10, for example.
The measurements can become very precise - perf 11.2, for example - so if you wish to specialize in U.S. stamps, for example, you should buy the most detailed perf gauge that you can find. If you have a more general interest, a less detailed gauge will allow you to measure most stamps.
Sometimes perf gauges are printed on advertising handouts or other items in the stamp hobby, on paper or cardboard. These gauges will not be very accurate, because paper shrinks or swells in relation to the amount of water in the air, and the measuring marks will shrink or swell also on a paper perf gauge. It is better to get a metal or plastic perf gauge, which will not react to changes in the level of humidity.
For more detailed information about perforations and gauges, check the general information pages in the standard stamp catalogues, or a good philatelic beginner's handbook.