AI Stamp ID: Centering and Margin Grading

December 16, 2025

Stamp centering and margin size are two of the most important visual factors that decide a stamp's overall quality and desirability. This guide explains how AI Stamp ID measures centering, how it uses margin symmetry and margin width, and how it decides an ideal margin target (M_target) for perforated and imperforate stamps.

1. Why Centering Matters

Centering describes how evenly the printed design sits within the margins or perforations of a stamp. Collectors value stamps with well-balanced, generous margins because they are more visually appealing and often scarcer.

2. Measuring Margin Symmetry

AI Stamp ID measures each of the four margins (Left, Right, Top, Bottom) in millimeters. To evaluate how well-centered the stamp is, the system compares opposite margins to see how closely they match in size.

Centering Score Formulas:

Horizontal Centering Score:

C_h = 100 × (1 − |L − R| / (L + R))

Vertical Centering Score:

C_v = 100 × (1 − |T − B| / (T + B))

A score of 100 is perfectly equal margins on that axis. The combined symmetry score averages horizontal and vertical alignment:

C_symmetry = (C_h + C_v)/2

3. Margin Size (Absolute Width)

Symmetry alone does not tell the whole story. A stamp with tiny margins can be symmetrical but still undesirable. Therefore, AI Stamp ID also evaluates absolute margin width by comparing the smallest margin on the stamp to a target margin width, called M_target.

Minimum Margin: m_min = min (L, R, T, B)

Margin Score: C_size = 100 × min (1, m_min / M_target)

4. What Is M_target?

M_target is a realistic reference margin for a particular stamp issue. Instead of using a fixed number, M_target adapts to differences in printing technology, production era, and stamp type.

There are two primary categories:

1. Perforated Stamps

For most perforated stamps worldwide, typical well-centered examples have margin widths between 0.8 mm and 1.2 mm. For these issues, AI Stamp ID uses:

M_target ≈ 1.0 mm

2. Imperforate Stamps

Imperforate stamps often feature much wider margins, sometimes 2–5 mm or more depending on era and country. For these issues, centering and appearance depend heavily on margin size. Typical targets are:

M_target ≈ 2.5–4.0 mm

AI Stamp ID will detect imperforate stamps and automatically adjust to this wider M_target value.

5. Combined Centering Score (0–100)

The final centering score blends symmetry and absolute margin size:

C_final = 0.7 × C_symmetry + 0.3 × C_size

This weighting ensures both factors influence the final grade, like traditional expert grading systems.

6. Centering Grade Bands

Score Range	Grade	Sales Card Code	Description
100	Gem	Gem	Perfect Centering
98-99	Superb	Superb	Visually Centered
95-97	Extremely Fine-Superb	XFSuperb	Exceptional centering and strong margins.
90–94	Extremely Fine (XF)	XFine	Beautiful centering, very strong margins.
80–89	Very Fine (VF)	VFine	Well-centered with typical margin sizes.
70–79	Fine–Very Fine (F–VF)	FVFine	Moderate imbalance, acceptable margins.
55–69	Fine (F)	Fine	Noticeably off-center, narrower margins.
40–54	Average (AVG)	Average	Weak centering and uneven margins.
0–39	Poor	Poor	Design touches or cuts into edges.

7. Jumbo Margin

Jumbo margins are margins bigger than the typical target margin (M_target)

A Jumbo stamp is one where:

The smallest margin is noticeably larger than what is typical for that issue.
The margins appear unusually wide in all directions.
Symmetry is still good, otherwise it's just "wide on one side."

To convert that into math, we use the ratio:

Ratio = m_min ÷ M_target

Where:

m_min = smallest margin among L, R, T, B
M_target = "great margin" reference for that issue (≈90th percentile)

Jumbo Margin Thresholds

Ratio (m_min ÷ M_target)	Category	Meaning
1.00 – 1.20	Above Average	Better than typical margins
1.20 – 1.40	Large Margins	Visually wide; often called "huge margins"
1.40 – 1.75	Jumbo	Clearly jumbo; wide on all sides
> 1.75	Super Jumbo / GEM Jumbo	Extremely rare; exceptional eye appeal

Jumbo margins only apply to stamps with centering grades of 90 or greater

8. Centering + Jumbo Margin Grade Bands

Score Range	Grade	Sales Card Code	Description
100	Gem	Gem-J or Gem-SJ	Perfect Centering
98-99	Superb	Superb-J or Superb-SJ	Visually Centered
95-97	Extremely Fine-Superb	XFSup-J or XFSup-SJ	Exceptional centering and strong margins.
90–94	Extremely Fine (XF)	XFfine-J or XFfine-SJ	Beautiful centering, very strong margins.
80–89	Very Fine (VF)	VFine	Well-centered with typical margin sizes.
70–79	Fine–Very Fine (F–VF)	FVFine	Moderate imbalance, acceptable margins.
55–69	Fine (F)	Fine	Noticeably off-center, narrower margins.
40–54	Average (AVG)	Average	Weak centering and uneven margins.
0–39	Poor	Poor	Design touches or cuts into edges.