What is the difference between AGS and GIA grading?

GIA grades color D–Z, clarity FL–I3, and cut Excellent through Poor based on proportion measurements plus a face-up appearance check. AGS Laboratories graded all four Cs on a single 0–10 numeric scale where 0 is Ideal, and graded cut on measured light performance using ray-tracing and ASET imagery rather than proportion buckets. AGS Laboratories closed in late 2022 and GIA acquired the AGS cut-grading IP, which now ships as the AGS Ideal Report digital supplement on eligible GIA reports.

Is AGS 0 better than GIA Excellent?

They measure different things. GIA Excellent confirms a stone's proportions, polish, and symmetry fall inside the top measurement bucket. AGS 0 confirms the stone returns light in the top-tier pattern under ray-traced ASET analysis. Roughly the top 10–15% of GIA Triple Excellent round brilliants also qualify for AGS 0 under the supplement. Every AGS 0 is GIA Excellent; not every GIA Excellent is AGS 0.

Did AGS Laboratories close?

Yes. AGS Laboratories ceased grading operations in late 2022 and GIA acquired the AGS intellectual property, cut-grading software, research staff, and Las Vegas facility. AGS Ideal cut science survived the transition and now ships as the digital AGS Ideal Report supplement on qualifying GIA reports for roughly $25 per stone. The non-profit American Gem Society — the trade association — still operates separately from the closed laboratory.

Does an old AGS certificate still hold value on resale?

Pre-2022 AGS Platinum reports on rounds still carry weight with informed trade buyers, particularly AGS 0 grades on signed cuts and hearts-and- arrows stones. Less-informed retail buyers may discount the paper because the issuing lab no longer exists; for a clean retail sale most sellers send the stone to GIA for a current report (which can then add the AGS Ideal supplement). On the trade side the original AGS 0 paper remains a real credential.

AGS vs GIA: Side-by-Side Grading Rubric, Methodology, and Resale Impact (2026)

The query AGS vs GIA almost always comes from the same moment: you're staring at a stone priced four or five figures and trying to decide which lab's paper is the one that actually defends the spend. The short version is that GIA and AGS were never grading the same thing the same way, and the 2022 closure of AGS Laboratories changed which report you can still get — but not which grading philosophy the trade respects. This piece is the side-by-side: the rubrics, the methodology contrast, the corporate timeline, and what each report does to resale price in 2026.

This article is the comparison spoke of our hub How to Read a GIA Diamond Report. For the full methodology deep-dive — AGS Laboratories history, the ASET light-performance system end-to-end, and the 2022 GIA acquisition timeline — see the AGS vs GIA authority hub. For the multi-lab buying decision that also folds in IGI, see GIA vs IGI vs AGS.

The side-by-side rubric

Dimension	GIA (Gemological Institute of America)	AGS Laboratories (pre-2022)
Color scale	D (colorless) → Z (light yellow / brown)	0.0 (colorless) → 10.0 (light color), 0.5 steps
Clarity scale	FL, IF, VVS1, VVS2, VS1, VS2, SI1, SI2, I1, I2, I3	0 (Ideal) → 10 (Poor), 1-point steps
Cut scale	Excellent, Very Good, Good, Fair, Poor	0 (Ideal) → 10 (Poor), 1-point steps
Cut methodology	Proportion measurements + polish + symmetry + face-up appearance check	Light performance: ray-traced brightness, contrast, dispersion, leakage, plus ASET imaging
Cut shapes graded	Round brilliants (full grade); fancy shapes get individual measurements but no overall cut grade	Round brilliants + qualifying fancy shapes (cushion, princess, emerald, oval) under the AGS Performance Grading Standard
Polish & symmetry	Excellent, Very Good, Good, Fair, Poor	0 → 10, 1-point steps
Lab status (2026)	Active; sole standard-setter after acquiring AGS IP	Closed late 2022; IP and science continue inside GIA as the AGS Ideal Report supplement
Report types still issued (2026)	GIA Diamond Grading Report, GIA Diamond Dossier, GIA Laboratory-Grown Diamond Report (no 4Cs since Oct 2025; Premium/Standard tiers), AGS Ideal Report digital supplement (~$25)	None — supplement only, issued on top of a GIA report
Trade shorthand	"Triple Ex" = Excellent cut + Excellent polish + Excellent symmetry	"AGS 000" = 0 cut + 0 polish + 0 symmetry on the legacy AGS Platinum Light Performance report
Authority reference	gia.edu — full report-check database, grading methodology PDFs	agslab.com — historical AGS Performance Grading Standard archived under the AGS Ideal Report at GIA

The rubric makes the substantive difference visible: GIA scales are categorical buckets, AGS scales were continuous numerics, and the cut grade in particular tested two different things — proportion conformity (GIA) versus measured light output (AGS).

How each lab actually decided what to print

GIA cut grade. The GIA cut grade for round brilliants is computed from a combination of seven proportion parameters (table %, depth %, crown angle, pavilion angle, star length, lower-half length, girdle thickness), polish, symmetry, and a face-up visual assessment performed by trained graders. The methodology is publicly documented in GIA's cut-grading system overview. The grade is conservative and reproducible: send the same stone through twice and you get the same letters back. The cost is granularity. Two stones can both earn "Excellent" and look meaningfully different in person because Excellent is a wide proportion range, not a performance verdict.

AGS cut grade. AGS Laboratories took the opposite approach: it ray-traced the actual stone, measured how light entered the crown, bounced inside the diamond, and exited as brightness, contrast, fire (dispersion), and leakage, and then graded the result on a 0–10 scale. A stone earned 0 (Ideal) only if its measured light output matched the AGS Performance Grading Standard reference pattern — confirmed with ASET (Angular Spectrum Evaluation Tool) hemisphere imaging, the red/green/blue map that shows where light is being returned, contrast-traded, or lost. That's why the trade still uses "AGS 0" as shorthand for the top tier of cut a round brilliant can reach: it isn't a measurement bucket, it's a verdict on what the stone does with light.

For the editorial desk's read on why this distinction continues to matter even with AGS Laboratories closed: "GIA Excellent says the stone is built right; AGS 0 says the stone performs. On any round above roughly $4,000 we want both verdicts on the paper, because the proportion check and the light-performance check fail in different ways and you cannot tell them apart by eye in a store-lit case." — CaratWire editorial desk, senior gemological editors reading GIA, AGS, IGI, SSEF, Gübelin, GRS and AGL reports weekly (see the byline page).

The 2022 closure: what actually happened

The corporate timeline matters because misinformation around it is one of the most common reasons buyers misjudge older AGS paper.

July 2022 — closure announced. AGS Laboratories (AGSL), the for-profit grading lab arm of the American Gem Society trade association, announced it would wind down standalone grading operations.
Late 2022 — operations cease. AGSL stopped issuing standalone AGS Platinum Light Performance reports. The Las Vegas grading facility, ray-tracing technology, ASET methodology, research staff, and the AGS Performance Grading Standard IP transferred to GIA under an acquisition agreement.
2023 — AGS Ideal Report launches inside GIA. GIA introduced the AGS Ideal Report, a digital supplement that can be added to an eligible GIA Diamond Grading Report or GIA Laboratory-Grown Diamond Report on qualifying round brilliants and select fancy shapes. The price is roughly $25 per stone. The grading criteria are the same AGS Performance Grading Standard the old AGS Platinum reports used.
2024–2026 — the trade adjusts. Pre-2022 AGS Platinum reports remain valid documents on the secondary market, especially among informed trade buyers. The American Gem Society itself, the non-profit trade association, continues to operate as a separate entity from the closed lab; an "AGS member jeweler" credential is about retailer ethics, not lab grading.

The misconception to avoid: AGS cut science did not die. It moved. A "GIA + AGS Ideal" report on a 2026 stone carries the same AGS 0 verdict the pre-2022 paper did — issued by the same software, against the same standard, often by the same research staff that ran AGSL.

Resale-price impact differential

This is the part of the AGS vs GIA question that actually affects what you pay and what you recover.

On naturals. GIA reports are the trade's pricing benchmark. The Rapaport list, the dominant per-carat reference, prices off GIA grades. A round natural with a clean GIA report is the most liquid resale instrument the diamond market has. AGS Platinum paper on a natural round trades at parity with GIA equivalents in the informed trade, but at retail counters that don't recognize the AGS name post-closure, sellers commonly absorb a 5–10% discount to move the stone — or pull a new GIA report on it.

The AGS Ideal supplement on a GIA-graded round. Adding the ~$25 AGS Ideal supplement to a GIA Triple Excellent round identifies the top 10–15% of stones in that bucket. Trade buyers will pay a 3–7% cut premium for the verified AGS 0 supplement on round naturals above 0.90 ct, because it isolates a stone you can actually see performing under spot lighting, the variety of light most engagement rings live under.

On lab-grown. GIA stopped printing 4Cs on lab-grown in October 2025 — the report became a binary Premium / Standard quality stamp. The AGS Ideal supplement is the most defensible cut credential you can attach to a lab-grown round in 2026, because there is no other independent light-performance grade on the document. For why this matters for total-cost math, see lab-grown diamond resale value in 2026.

On the original AGS Platinum reports. Pre-2022 AGS 0 paper on a signed cut (Hearts on Fire, A. Jaffe, original Whiteflash A CUT ABOVE, etc.) holds its value among trade buyers who know the brand. On generic resale to consumer buyers post-closure, expect to either accept a discount or pay for a fresh GIA report plus AGS Ideal supplement.

The numeric rule of thumb. For a 1.00 ct round, GIA G/VS1 Triple Excellent, retail comp $7,500/ct:

Same stone with a GIA report only: $7,500/ct comp band.
Same stone with GIA + AGS Ideal 0 supplement: $7,725–$8,025/ct comp band (3–7% premium).
Same stone on a pre-2022 standalone AGS Platinum 0 report at a non-trade retailer: $6,750–$7,125/ct effective recovery (5–10% discount for paper unfamiliarity).
Same stone on the same pre-2022 AGS Platinum 0 report sold to a trade buyer who recognizes the credential: $7,500/ct, parity with GIA.

For the broader per-carat picture those numbers anchor against, see the live 2026 diamond price-per-carat index.

How to translate one scale into the other

There is no clean one-to-one conversion between the AGS numeric scales and the GIA categorical scales, and any source that claims otherwise is selling something. The reliable trade rules of thumb, refined against GIA's own cut-grading methodology and the AGS Performance Grading Standard now archived under AGS Laboratories at GIA:

Cut translation (rounds):

GIA Triple Excellent + AGS Ideal 0 supplement = genuine top tier; roughly the top 10–15% of GIA Triple Excellents.
GIA Triple Excellent without AGS 0 = excellent stone inside the proportion bucket, not the light-performance one.
GIA Excellent with both polish and symmetry less than Excellent ≈ AGS 1 to AGS 2.
GIA Very Good ≈ AGS 2 to low AGS 3. When a GIA Very Good cut round is actually worth buying — melee, side stones, small solitaires — has its own tier-by-tier walkthrough separate from this table.
GIA Good ≈ AGS 4 to AGS 5.
GIA Fair/Poor ≈ AGS 6 and above.

Color translation:

GIA D ≈ AGS 0.0
GIA E ≈ AGS 0.5
GIA F ≈ AGS 1.0
GIA G ≈ AGS 1.5–2.0
GIA H ≈ AGS 2.5
GIA I ≈ AGS 3.0–3.5
GIA J ≈ AGS 4.0
GIA K–M ≈ AGS 4.5–5.5
GIA N–R ≈ AGS 6.0–7.5
GIA S–Z ≈ AGS 8.0–10.0

Clarity translation:

GIA FL ≈ AGS 0
GIA IF ≈ AGS 1
GIA VVS1 ≈ AGS 2
GIA VVS2 ≈ AGS 3
GIA VS1 ≈ AGS 4
GIA VS2 ≈ AGS 5
GIA SI1 ≈ AGS 6
GIA SI2 ≈ AGS 7
GIA I1 ≈ AGS 8
GIA I2 ≈ AGS 9
GIA I3 ≈ AGS 10

Apply the cut translation with the most care — that's where the methodology gap is largest and the dollars move most. Color and clarity translations are tight because both labs were measuring the same physical property; they just printed the answer in different vocabularies.

When the AGS Ideal supplement is worth paying for

Three cases, all anchored to dollars rather than principle.

Round naturals priced above roughly $4,000–$5,000. The cut premium is a meaningful slice of the spend and the harder test separates the top performers from the rest of the Excellent bucket.
Any round marketed as "super ideal" or "true hearts and arrows". Make the seller put the AGS 0 supplement on it before you accept the cut premium. The supplement, not the marketing copy, is what verifies the claim.
Lab-grown rounds where you're paying for top visual performance. GIA's Premium/Standard tiers don't grade cut granularly anymore; the AGS Ideal supplement is the most defensible light-performance credential on a 2026 lab-grown report.

Skip the supplement on rounds under that price band — GIA Excellent is enough — and skip it on fancy shapes that don't qualify. It is a targeted upgrade, not a universal one.

What to ask at the counter

A short script for the AGS vs GIA decision specifically:

"Which lab graded this, and may I see the full report — not just the inscription number?"
"Is the AGS Ideal cut supplement attached? If not, can one be pulled for this stone before purchase?"
For a pre-2022 standalone AGS Platinum report: "What is the report number, and may I verify it against AGS Laboratories' historical database now archived at GIA?" The lookup lives at agslab.com.
"Does the report number laser-inscribed on the girdle match this paper?" Verify the GIA number on GIA Report Check before money moves.
For any round being marketed as a "branded super ideal": "Show me the AGS 0 verification, not the brand's internal cut report."

The one-line summary

GIA Excellent is a measurement bucket; AGS 0 is a light-performance verdict; the difference between them is the difference between a well-proportioned round and a round that actually performs — and in 2026 you can get both verdicts on a single GIA + AGS Ideal Report for about $25 extra. If you already own a stone with a pre-2022 AGS Platinum Light Performance report and want the full lab history plus a line-by-line read of the legacy document, see the AGS cut grade history and legacy-report guide. For the line-by-line GIA report walkthrough, return to the hub article on reading a GIA report. For the three-lab buying decision that adds IGI to the picture, see GIA vs IGI vs AGS. For the fluorescence call that interacts with cut performance under daylight, see GIA fluorescence grades explained.