How to Use a Perforation Gauge

Two stamps can look identical at a glance — same design, same colour, same year of issue — yet be entirely different catalogue entries with dramatically different values. The difference is often the perforation gauge. Learning to measure perforations accurately is one of the most useful skills a collector can develop, and with the right tool it takes about thirty seconds.

What Perforation Gauge Means

Perforations are the rows of small holes punched around a stamp’s edges to allow separation from a sheet. The perforation gauge is the measurement of how many of these holes — or more precisely, the centres of these holes — fall within 2 centimetres. A stamp described as “perf 14” has 14 perforation holes per 2cm. A stamp at “perf 11” has 11 — a coarser, more widely spaced perforation that is immediately visible to the trained eye.

This measurement was standardised by the French philatelist Jacques Legrand in the 1860s, and the system has been universal ever since.

Types of Perforation Gauge

Instanta Sliding Gauge. The collector standard. A transparent slide moves over a printed backing card; you align the stamp and read the gauge at the matching line. Measures in half-point increments (11, 11½, 12, 12½, and so on) across the full range used in stamp production. Manufactured in the UK; costs around £12–15.

Printed card gauge. A card printed with rows of dots in each gauge increment. You lay the stamp alongside each row until the dots align with the perforation holes. Inexpensive and functional, though slightly less precise than a sliding gauge for half-gauge readings.

Digital/electronic gauge. Specialist gauges using optical measurement, produced by suppliers such as Rolland Gauge. Highly accurate to fractions of a gauge point and valuable for distinguishing difficult varieties. The cost — often £50 or more — is justified only for collectors working intensively with perforated varieties.

Step-by-Step: How to Measure

1. Place the stamp face-up on the gauge. Using tongs, position the stamp on the Instanta’s transparent slide so that a horizontal edge (top or bottom row of perforations) aligns over the scale.

2. Slide or align until the dots match the holes precisely. On the Instanta, move the slide until the printed dots on the scale line up exactly with the centres of the perforation holes. On a card gauge, move the stamp along until you find the matching row.

3. Read the number at the matching line. This is your horizontal gauge — the measurement for the top and bottom edges of the stamp.

4. Rotate the stamp 90 degrees and repeat. Measure the left or right edge. This gives you the vertical gauge.

5. Compare the two readings. If both gauges are the same (e.g., perf 14 on all sides), the stamp is described simply as “perf 14.” If horizontal and vertical measurements differ, you have a compound perforation.

What the Number Means

Higher gauge = more holes per 2cm = finer, closer perforations. Lower gauge = fewer holes = coarser perforations with more paper between each hole.

Perf 11 (coarse) was common on early US stamps. Perf 14 (fine) was the standard for many British Commonwealth issues. Perf 13½ is extremely common on modern offset-printed issues worldwide.

Compound Perforations

A compound perforation occurs when the top/bottom edges and the left/right edges have different gauges. A stamp described as “perf 14 × 13½” was perforated 14 horizontally (top and bottom) and 13½ vertically (left and right). This happens when stamps are perforated by machine in two separate passes — first horizontally across the sheet, then vertically — and different machines or comb heads are used.

Compound perforations create distinct catalogue varieties. The US 1902 definitive series is a classic example where gauge combinations create multiple separately listed entries.

Why Gauge Matters: Real Examples

British Penny Red (SG 43–44). The Penny Red perforated 14 is one of the most common British stamps in existence. The same stamp perforated 16 (SG 44, perf 16) is rare and valuable — the difference of two gauge points represents a catalogue value difference of several hundred pounds.

US 1908–1921 Washington–Franklin definitives. This long series was issued with several gauge variations — perf 12, perf 10, perf 11, and combinations. Each combination of gauge, paper type, and watermark creates a separate Stanley Gibbons or Scott catalogue number, with values ranging from a few cents to several hundred dollars.

Common Gauges by Country and Era

• Great Britain early issues (Victorian line-perforated): 14 is the most common; 16 and 15½ × 15 also occur.
• GB Machin definitives and modern issues: 15 × 14, or phosphor-reactive comb perf 14.
• US classic issues (pre-1920): perf 12 is the standard; perf 10 and perf 11 create varieties.
• Australia and Commonwealth: perf 14 (comb) is dominant across the mid-20th century.
• Coil stamps: typically perforated on only two sides (top and bottom, or left and right), making them immediately distinguishable from sheet stamps.

Next Steps

Perforations are one identification tool; watermarks are another — and often equally important for establishing a stamp’s true identity and value. Read Watermark Detection for Stamp Collectors for the techniques and tools needed to reveal these hidden marks.