Stamp perforation gauge

1. Pick up the stamp with tongs and lay it face up next to, or on top of, the gauge.
2. Line up one horizontal edge with a row. Check the holes at both ends of the edge, not just the first few. If they drift apart halfway, try the next row.
3. Note the gauge, then turn the stamp and measure a vertical edge.
4. Write it the way catalogs do: horizontal first, then vertical. A stamp that gauges 11 on all sides is simply “perf 11”.

Counting holes on the stamp itself only works if the edge happens to be exactly 2 cm long, which is why collectors use a gauge.

The Scott catalogs print the perforation and watermark in the line that introduces each set, and flag any change in bold. Some long-running series were perforated in several gauges. The US Washington-Franklin issues, for example, come in gauges of 8½, 10, 11, 12 and 12½.

Same portrait, same color, different gauge: that can be a different catalog number and a very different price. If you plan to look up a stamp's value, measure the perforation first. Then compare with a guide such as our stamp value guides.

Gauges in use run wider than this tool. Perf 2 appears on 1891 stamps of Bhopal and perf 18 on stamps of the Malay States in the early 1950s. Most stamps you will handle fall between 10 and 16.

• Harrow perforation punches a whole sheet in one stroke, with pins arranged in little boxes the size of each stamp.
• Comb perforation punches one row at a time, with pins shaped like a comb: the top and both sides of each stamp in the row in a single strike.
• Line perforation uses a single row of pins. The sheet is perforated strip by strip, then turned 90 degrees for the other direction.

Harrow and comb perforation give every stamp the same, regular corners. Line perforation leaves irregular corners where the rows cross. The Austrian Philatelic Society's guide makes a point worth keeping: decide the perforation type from those characteristics first. A line-perforated stamp is line-perforated whatever the gauge reads.

That is why the tool asks which edge you are measuring. Tap the matching row for the top and bottom, switch to the sides, and tap again. The result reads like a catalog entry, for example “Perf 11 × 10½”.

Some stamps are perforated on one pair of opposite sides and imperforate on the other, usually because they come from coils or booklet panes. That is how those formats were made, not damage.

Britain used machines for perforating postage stamps from January 1854, after trials that began with Henry Archer's machine. Some issues were rouletted instead, with small cuts in the paper rather than holes.

Watch for “imperforate between” errors, where a pair is not separated on all sides. Rare stamps are often expertized in case they have been reperforated. If a perforation variety would make a stamp valuable, read our guide to stamp appraisal before you sell.