ACE Grading Centering Standards: Why Its Scores Are So Transparent

ACE Grading's centering standard for a 10 Gem Mint is centering "less than a 60/40 split," and it applies that to every opposite pair of borders — left/right and top/bottom, on the front and on the back. Below that, ACE publishes a plain per-grade ladder: 65/35 front and 70/30 back for a 9, 70/30 and 75/25 for an 8, 75/25 and 80/20 for a 7, 80/20 both sides for 6 through 4, and 85/15 both sides for 3 through 1.

What makes ACE different from PSA, BGS, CGC or SGC is not the numbers. It is that ACE tells you how it gets them. Its grading-scale page says centering is "calculated using 1/1000th of a millimeter accuracy measurements," converted into "a percentage for Left, Right, Top and Bottom centering for both the front and back of the card." Its centering blog describes "digital measuring via microscopy." Instead of a grader judging that a card looks "approximately 55/45," ACE produces a number and checks it against a threshold.

That matters to you for one practical reason: if you can measure your card accurately at home, you can predict ACE's centering result far more reliably than you can predict PSA's. This guide lays out the official ACE tolerances, the measurement method, the OC modifier rule, the three-border workaround, and how the ACE scale lines up against PSA and TAG.

ACE Grading centering tolerances by grade

Everything in this table comes from ACE's published grading scale. Ratios are "no worse than" thresholds for the worst opposite pair of borders.

Three things stand out.

The 10 line is "less than 60/40," not "approximately 55/45." ACE's own blog uses a Charizard VSTAR whose worst measurement was "59.63%" as an example of a card that still earned Gem Mint 10. On the front, that is a looser top standard than PSA (approximately 55/45), BGS 9.5 (55/45 both ways), CGC Gem Mint 10 (approximately 55/45), SGC 10 Gem (55/45) or TAG Gem Mint 10 (~55/45).

The back is held to the same 60/40 for a 10. This is where ACE is tighter than almost everyone. PSA allows 75/25 on the reverse for a 10, CGC allows 75/25, TAG allows ~70/30 (sports) or ~65/35 (TCG) for Gem Mint, and BGS 9.5 allows 60/40. Only BGS Pristine 10 (55/45 back) and TAG Pristine (~54.5/45.5 or ~52/48) are stricter on the back than ACE's 10.

Grades 6 through 4 and 3 through 1 share thresholds. Below a 7, ACE stops using centering to separate grades; corners, edges and surface do that work. If your card is a 5 or 6 candidate, centering between 75/25 and 80/20 simply is not the thing that decides it.

How ACE measures centering: 1/1000 mm and a percentage for every side

ACE's description of its method is the most specific any major grader publishes. Paraphrasing the grading-scale page and the centering blog:

1. ACE measures "the distance between the card edge and the card border on opposite edges in any of the four opposite edge pairings" — left/right front, top/bottom front, left/right back, top/bottom back.
2. The measurement is digital, via microscopy, "to within 1/1000th of a millimetre."
3. The raw distances are turned into a percentage for left, right, top and bottom, on both faces.
4. The worst opposite pair is what the grade threshold is applied to ("any opposite pair" in the 9 Mint wording).

The math is the same formula you use at home. For a pair of opposite borders, the ratio is the larger border divided by the sum of both:

• Left border 2.9 mm, right border 2.1 mm → 2.9 ÷ (2.9 + 2.1) = 58% → 58/42
• Top border 2.4 mm, bottom border 2.6 mm → 2.6 ÷ 5.0 = 52% → 52/48

The card above has a worst pair of 58/42. Under ACE's scale that is still "less than a 60/40 split," so centering does not block a 10. Under PSA's approximately 55/45 front standard, the same card is a 9 candidate on centering alone. That single example explains most of the "ACE gave me a 10, PSA gave me a 9" stories collectors share.

Because ACE reports per-side percentages rather than a single judgment, the precision of your own measurement becomes the limiting factor. On a card with roughly 2.5 mm side borders, a 0.25 mm error on one side moves the ratio about five points — enough to cross the 60/40 line. Measure out of the sleeve, flat, at two points on each side, and use a free card centering calculator or a scanner-and-pixels method rather than a ruler if the card is anywhere near 60/40. Our how to measure card centering guide covers all four methods.

What the ACE standard means in millimeters

To make the thresholds concrete, here is where the ACE grade lines fall for two common border widths. Numbers are the border on the wide side for a pair whose combined width is fixed.

Read it like this: on an English Pokémon card with about 5.5 mm of combined side border, ACE's 10 line is crossed when the wide side reaches 3.3 mm and the narrow side drops to 2.2 mm. That is a visible difference but not a dramatic one. Our centering ratios in millimeters article expands this to every common ratio and border style.

The ACE OC modifier: when centering is two grades behind

ACE's rule for the Off-Center modifier is written down, which is unusual. From the grading scale: "The Off-Center modifier is given to a card where the grade for centering is 2 grades or more below the overall card grade," and ACE handles it by "appending OC to the grade."

Work through the logic with the ACE ladder:

• A card measures 72/28 on the front. On the centering scale, 72/28 is worse than the 70/30 limit for an 8 but within the 75/25 limit for a 7, so the centering grade is 7.
• If the rest of the card — corners, edges, surface — supports a 9, the overall grade is two steps above the centering grade. ACE's rule says the result carries the modifier: 9 OC.
• If instead the centering measured 68/32, the centering grade is 8, only one step below 9, and no OC is added; the card is simply graded with that centering factored in.

Compare this to PSA, whose 2021 customer update says the OC qualifier "will be assigned at the grader's discretion, and most typically will impact the numerical grade rather than carrying a qualifier." ACE's approach is rule-based: you can calculate in advance whether your card will wear the OC tag. If you are deciding between the two and your card is a strong card with weak centering, that predictability is worth knowing about. Our off-center vs miscut qualifiers article compares how each grader handles the label and what it does to value.

Three-border cards: ACE's reconstruction method

Some cards only show three measurable borders — one edge bleeds to art, a design element covers a border, or the layout is asymmetric by design. ACE's centering blog explains the workaround: "On cards where only three borders are visible… we calculate the average border size with the known pair (left and right) and then… figure out what the size of the border should be."

Here is that method as a worked illustration (our numbers, ACE's logic):

1. Left border measures 2.4 mm, right border 2.0 mm. The known pair averages (2.4 + 2.0) ÷ 2 = 2.2 mm.
2. ACE treats 2.2 mm as the expected border size for the missing edge. If the visible top border is 2.6 mm, the top/bottom pair is estimated at 2.6 mm plus an inferred bottom of about 1.8 mm (so the pair totals 4.4 mm, the same as a centered 2.2 + 2.2).
3. Centering for that axis: 2.6 ÷ 4.4 = 59% → roughly 59/41, which would still sit inside ACE's 10 threshold.

The honest caveat: this assumes the missing border was designed to be the same width as the known pair. When the top and bottom borders are designed differently from the sides, the estimate is only as good as that assumption. It is still more transparent than any other grader's published position — PSA, BGS, CGC and SGC publish nothing on borderless or three-border measurement. For the practical side of choosing reference edges when a border is missing, see how to measure centering on full-art and borderless cards.

ACE vs PSA vs TAG: the same card, three answers

The three graders that matter most for a centering comparison are PSA (the volume leader), TAG (machine-measured, 1000-point score) and ACE (microscopy-measured, per-side percentages). Top-grade thresholds from each company's official page:

Run three real-world cards through it:

• Front 58/42, back 55/45. ACE: centering supports a 10. PSA: front exceeds ~55/45, so a 9 on centering unless the grader's eye-appeal discretion intervenes. TAG: worse than ~55/45 front, so Mint 9 territory on centering.
• Front 54/46, back 68/32. ACE: back fails the 60/40 line for a 10, centering grade 9. PSA: front and back both inside the 10 limits (~55/45 and 75/25). TAG: front inside ~55/45; back inside ~70/30 for sports but outside ~65/35 for TCG, so a sports card passes and a TCG card does not.
• Front 51/49, back 52/48. All three clear their Gem Mint lines; TAG Pristine is the only one that demands this level on the front, and it would need the back within ~52/48 for a TCG card.

The pattern: ACE is the most forgiving on the front and the least forgiving on the back at the 10 level. PSA is the opposite. TAG sits between them and splits sports from TCG. If your card has a perfect front and a lazy back, PSA or TAG treats you better; if the front is 57/43 or 58/42 and the back is tight, ACE is the only scale on this table that still reads 10. For the full side-by-side, use our centering tolerance by grade table and the PSA 10 vs BGS 9.5 vs CGC 10 vs TAG 10 crosswalk. For TAG specifically, see TAG grading centering explained.

Why "transparent" is the right word — and what it does not mean

Transparent does not mean lenient, and it does not mean automatic. Three clarifications collectors often miss:

ACE's 60/40 is a hard line for the centering score, not a promise of a 10. The overall grade still depends on corners, edges and surface. A card at 59/41 with a soft corner is not a 10 anywhere.

The per-side percentages are only as useful as your own measurement. ACE measures to 1/1000 mm under a microscope; you are measuring with a ruler, a caliper or a photo. If your home reading is 59/41, the true value could easily be 60.5/39.5. Treat anything within about two points of a threshold as a coin flip and measure again with a better method.

ACE publishes per-side percentages; most graders do not. PSA's label shows a grade and, when applicable, a qualifier. BGS shows a centering subgrade on request. TAG's DIG report shows front and back centering subgrades with measurements. ACE's stated approach produces a left, right, top and bottom percentage for both faces. Collectors report that those figures are visible on the card's ACE report; if knowing your exact numbers after grading matters to you, that is a genuine point of difference.

How to pre-check a card against the ACE scale

1. Remove the card from any sleeve or holder. Sleeves add edge shadow and shift the apparent border.
2. Photograph it straight down in even light, or scan it flat. Perspective distorts one side relative to the other.
3. Measure each border from the cut edge to the outer printed border at two points along the side; average them. This catches tilt and diamond cuts.
4. Compute left ÷ (left + right) and top ÷ (top + bottom), front and back. Write all four ratios down.
5. Take the worst of the four. If it is better than 60/40, ACE's centering standard for a 10 is met. If it is between 60/40 and 65/35 front or 70/30 back, the centering score caps at 9.
6. Work out the centering grade and compare it with your honest estimate of the rest of the card. If centering is two or more grades lower, expect the OC modifier.

The free card centering calculator does the ratio math from a photo and maps the result to PSA, BGS, CGC, SGC and TAG thresholds; you can read the ACE result off the table above using the worst ratio it gives you.

Bottom line

• ACE's published centering standard for a 10 Gem Mint is "less than a 60/40 split" on every opposite pair, front and back; 9 Mint is 65/35 front and 70/30 back; 8 is 70/30 and 75/25; 7 is 75/25 and 80/20.
• ACE measures with digital microscopy "to within 1/1000th of a millimetre" and calculates a percentage for left, right, top and bottom on both faces — the most specific method description any major grader publishes.
• The OC modifier is rule-based: it is appended when the centering grade is two or more grades below the overall grade.
• Compared with PSA and TAG, ACE is looser on the front of a 10 (60/40 vs ~55/45) and stricter on the back (60/40 vs 75/25 or ~65–70/30).
• Three-border cards are handled by inferring the missing border from the average of the known pair, a documented method with a known assumption.
• Your home measurement is the bottleneck: within two points of a threshold, remeasure with a scan or a photo tool before deciding where to submit.

Frequently asked questions

What centering does ACE Grading require for a 10?+

ACE's published scale says a 10 Gem Mint will have centering that is less than a 60/40 split, on both the front and the back. That is looser than PSA's approximately 55/45 front standard for a Gem Mint 10, but ACE applies it to every opposite pair of borders, including the back, where PSA allows 75/25.

How does ACE Grading measure centering?+

ACE states that it measures the distance between the card edge and the printed border on opposite edges using digital microscopy to within 1/1000th of a millimetre, then converts those measurements into percentages for left, right, top and bottom on both the front and back of the card. The worst opposite pair is what the grade is checked against.

What does the OC modifier mean on an ACE grade?+

ACE appends OC (Off-Center) to a grade when the card's centering grade is two grades or more below the overall grade. So a card that is otherwise a strong 9 but whose centering only supports a 7 is labeled rather than simply dropped. It tells a buyer the number reflects the rest of the card, not its centering.

Is ACE stricter or looser on centering than PSA?+

On the front, ACE's 10 threshold (better than 60/40) is looser than PSA's approximately 55/45. On the back, ACE is stricter: it wants better than 60/40 on the reverse too, while PSA allows 75/25 for a Gem Mint 10. For grades 9 and below the two scales are within roughly five points of each other.

How does ACE grade centering on cards with only three visible borders?+

ACE's centering blog explains that when only three borders are visible it calculates the average border size from the known opposite pair, then uses that to estimate what the missing border should be, and derives the centering from there. It is an estimate, so small differences in the visible borders move the result more than on a four-border card.

Can a 59/41 card still get an ACE 10?+

Yes, if everything else supports a 10. ACE's own example is a card whose worst measurement was 59.63 percent, which still received Gem Mint 10 because the standard is centering that is less than a 60/40 split. The same card would miss PSA's approximately 55/45 front requirement for a 10.

Sources & further reading

• ACE Grading — Grading Scale
• ACE Grading blog — Centering: An ACE Explanation
• PSA Grading Standards
• TAG Grading — Grading Rubric
• Beckett Grading — BGS Grading Scale