01Decisive
The scale runs downward
AGS 0 is Ideal — the best grade on the scale. Any description treating a low AGS number as a low grade is wrong, and it is the commonest misunderstanding in the category.
Lovenhall Diamond
Verify a AGS report
The cut-grading specialist, whose zero-to-ten scale is not the same language as everyone else's.
Founded 1934Las Vegas3 weighted checks
The American Gem Society Laboratories built their reputation on cut grading, using a numerical scale from 0 to 10 where 0 is Ideal — the reverse direction from every other grading vocabulary, and the source of a great deal of confusion. An AGS 0 cut grade is the top of the scale, not the bottom.
AGS's light-performance analysis was for years the most rigorous cut assessment available, and AGS Ideal stones command a premium among buyers who care about how a diamond behaves in light rather than how it reads on paper. The laboratory's operations have since been folded into GIA, which is worth knowing when handling older AGS documents.
Verification follows the same pattern as the other laboratories: a report number, a lookup, and an inscription to match against the stone.
The maker's own markAt a glance
Reading an AGS report and its 0-to-10 scale
AGS grades cut, colour and clarity each on a 0 to 10 scale where 0 is the best. That inverts the intuition most buyers bring from clarity letters and colour letters, and a seller who describes an AGS 0 as a poor grade is either confused or hoping you are.
AGS reports carry a number that can be verified, and many AGS-graded stones carry a laser inscription on the girdle carrying that number. Match the inscription and the measurements to the stone as with any laboratory.
Because AGS Laboratories' operations were absorbed into GIA, older AGS reports remain valid documents describing the stone as graded at the time. Treat them as historical grading records and, for a purchase of consequence, consider a current report alongside.
| AGS grade | Meaning | Rough equivalent elsewhere |
|---|---|---|
| 0 | Ideal | Excellent |
| 1 | Excellent | Excellent to Very Good |
| 2 | Very Good | Very Good |
| 3 – 4 | Good | Good |
| 5 – 7 | Fair | Fair |
| 8 – 10 | Poor | Poor |
The scale runs the opposite way to the letter grades most buyers know. Zero is the top.
The checks
How AGS is read
Ordered by how much each one settles. The decisive checks are the ones worth your first five minutes; the supporting ones only matter once those are clean.
02Decisive
Report verification and inscription
The report number should verify and should match a laser inscription on the girdle. Match the measurements to the stone as well, since verification alone does not defeat report swapping.
03Strong
Light performance analysis, where present
AGS's cut grading includes a light-performance assessment that other laboratories historically did not offer. Its presence on a report is a genuine differentiator and part of why AGS Ideal stones carry a premium.
Questions we are asked
- What does AGS 0 mean?
- Ideal — the top grade on the AGS scale, which runs from 0 at the best to 10 at the worst. It is the opposite direction from the letter grades used for colour and clarity elsewhere.
- Is an AGS report as good as a GIA report?
- AGS was the specialist in cut grading and its light-performance analysis was for years the most rigorous available. Its operations have since been folded into GIA, so older AGS reports remain valid historical grading records.
The other laboratories and houses the room reads
Free tools of the room
Lovenhall DiamondRead the stone itself
The checks tell you how it was made. The instrument tells you what it appears to be, and roughly what its kind fetches.
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