The weakest-link rule
The overall grade does not meaningfully exceed the worst of the four criteria. Three 10s and a 7 do not make a 9 — they make something close to 7.5.
Grade prediction
A grade is not a general impression: it is the result of precise thresholds applied to four criteria. Understand the thresholds and you can anticipate the outcome.
In short
A grade combines four criteria assessed on both faces: centering, corners, edges and surface. The dominant rule is the weakest link — the lowest-scoring criterion caps the overall grade regardless of how good the others are. PSA requires 55/45 to 60/40 front centering and 75/25 back for a 10; 60/40 to 65/35 front corresponds to the 9 threshold.
PSA's published centering thresholds
Centering is the only publicly quantified criterion, which makes it the starting point of any estimate.
| Grade | Name | Front centering | Back centering |
|---|---|---|---|
| 10 | Gem Mint | 55/45 to 60/40 | 75/25 |
| 9 | Mint | 60/40 to 65/35 | 90/10 |
| 8 | Near Mint-Mint | 65/35 to 70/30 | 90/10 |
| 7 | Near Mint | 70/30 | 90/10 |
| 6 | Excellent-Mint | 70/30 | 90/10 |
Source: PSA published grading standards. Other companies' tolerances differ.
The four criteria and their real weight
Centering
Measurable and objective, and most often the limiting factor. It is judged on front AND back margins, and it cannot be improved.
Corners
All four corners on both faces. A single soft corner is enough to block a 10. The criterion most sensitive to handling.
Edges
Cut regularity and absence of whitening. Critical on dark borders, where the smallest chip is visible.
Surface
Scratches, handling marks, creases, print defects. The hardest criterion to assess from a photo.
The rules that govern the final grade
The disqualifying defect
A crease running through the card, a tear or obvious handling damage caps it at a low grade regardless of everything else.
Qualifiers
Some companies add a qualifier (OC for off-center, MK for mark, ST for stain) flagging an isolated defect on an otherwise excellent card.
Subgrades
BGS assigns a grade to each of the four criteria on top of the overall grade. The BGS 10 Black Label requires all four subgrades at 10 — which is why it is so rare.