Perforation Gauge

A perforation gauge is an indispensable tool for any stamp collector, used to count the number of perforation holes (or teeth) in a span of two centimetres along the edge of a stamp. Because many stamps exist in multiple perforation varieties that can look identical to the naked eye but differ significantly in catalogue value, a reliable gauge is as essential as a magnifier in a serious philatelist’s toolkit.

What the Number Means

The gauge number corresponds directly to the count of holes — or equivalently, the count of “teeth” (the paper points between holes) — in exactly 2 cm. A stamp measuring “perf 14” has 14 holes per 2 cm. Smaller numbers mean fewer, larger holes and therefore larger teeth; higher numbers mean finer, more closely spaced holes. Most classic 19th- and early 20th-century stamps fall in the range of perf 11 to perf 15, while some early issues were as coarse as perf 9 or as fine as perf 16.

When a stamp has different measurements on horizontal and vertical sides, it is described with a compound perforation: the horizontal measurement is always given first, then the vertical. For example, “perf 14 × 13½” means 14 holes per 2 cm along the top and bottom edges, and 13½ along the left and right sides.

Types of Perforation Gauge

Printed card gauges are the most traditional type. A ruled scale printed on card or acetate shows dots or lines at precise spacings. You align a row of perforations with the scale until the dots line up perfectly with the holes, then read off the number. These are inexpensive and durable, and they remain the most widely used type. The Gibbons gauge and the Instanta transparent gauge are classic examples.

The Instanta sliding gauge features a transparent acetate strip with rows of dots at different spacings. Sliding the stamp along the strip until a row matches the perforations gives a direct reading. Its transparency means you can see both the stamp design and the gauge lines simultaneously, making alignment easier.

Electronic and digital gauges appeared in the late 1990s and allow a stamp to be scanned or placed on a sensor pad; software calculates the perf measurement automatically. The Philatool electronic gauge was one of the first widely available digital options. These are accurate to a fraction of a gauge point and reduce user error, but cost significantly more than card gauges.

How to Use a Perforation Gauge

1. Place the stamp — right way up — on the gauge, with one edge aligned horizontally along the scale.
2. Move the stamp slowly up or down (on a card gauge) until the tips of the stamp teeth line up precisely with the dots or lines on the gauge.
3. Read the number at the position where the alignment is exact. If the perforations fall halfway between two numbers, the gauge is written as a fraction or decimal (e.g. 13½ or 13.5).
4. Repeat for the opposite side of the stamp to check for compound perforations.
5. For stamps on cover, measure carefully without removing the stamp — perforations are visible even when affixed.

Why the Gauge Matters

Some of the most significant stamp varieties in philately are distinguished solely by perforation. The British 1858–79 Penny Red plate numbers, for instance, were issued in both perf 14 and perf 16 versions, and some plate-and-perf combinations are major rarities. In US philately, many classic issues from the 1850s through the 1880s exist in perf 12, perf 15, and intermediate gauges, each listed separately in Scott and Gibbons catalogues at very different valuations.

Perforation type (line, comb, or harrow) also matters alongside the gauge number. Measuring coil stamps requires care because only two sides are perforated — the other two are straight, cut edges.