Research & evidence

Asscher Proportion Reference

A sourced framework for ratio, depth, table and finish signals

Updated: September 6, 2026ResearchMethodology disclosed

Bottom line

Asscher proportions are best used as screening signals, not a substitute for visual evaluation. GIA currently gives its overall cut grade to standard round brilliant diamonds, while other shapes are treated as fancy shapes without an overall GIA cut grade.

Evidence classification: The GIA cut-grade limitation below is a primary-source fact. The Asscher ranges in the table are editorial screening ranges—not GIA grades or universal beauty thresholds.

Where the screening ranges come from

The numerical bands on this page are AsscherDiamond.com editorial screening rules. They are not copied from a GIA “ideal Asscher” chart, because GIA does not currently issue an overall cut grade for fancy shapes. We use these ranges to narrow a candidate list, then require report measurements and face-up inspection before making a quality judgment.

Reproducibility rule: another reviewer can reproduce the screening decision from the published bands, but not the final visual judgment from numbers alone. The final decision requires the candidate’s own images/video and grading report.

Reference table

Signal	Practical starting zone	Evidence type	Use
Length-to-width ratio	About 1.00–1.05	Editorial screening range	Classic near-square outline
Total depth	Often low-60s to low-70s	Editorial screening range	Flag unusually deep/shallow candidates for closer review
Table	Often mid-50s to mid-60s	Editorial screening range	Compare top-facet openness and pattern
Polish	Very Good–Excellent preferred	Editorial preference using lab finish grade	Finish-quality screen
Symmetry	Very Good–Excellent preferred	Editorial preference using lab finish grade	Facet/outline alignment screen
Video / face-up imagery	Required for final decision	Editorial methodology	Windowing, extinction, contrast and windmill coherence

What GIA actually says about cut grading

GIA states that diamond cut grades are given to round brilliant diamonds because their facet pattern is standardized; other shapes are fancy shapes. GIA’s laboratory description likewise says it provides a cut quality grade only for standard round brilliants in the D-to-Z color range. This is why a seller’s “ideal Asscher” label should not be confused with an official GIA overall cut grade.

Why the ranges are deliberately broad

A step-cut diamond is a three-dimensional optical system. Depth and table alone do not encode crown height, pavilion relationships, facet placement, corner proportions or how contrast changes as the diamond moves. Tightening a spreadsheet filter can create false precision: it may remove visually excellent stones while retaining weak ones.

How we use the table

Confirm the outline is square enough for the buyer’s preference.
Use depth/table as comparative flags, not pass/fail grades.
Compare millimeter spread at the same carat weight.
Inspect persistent windowing and broad dead zones in motion.
Verify grading-report data independently.

Primary references

Claim-to-source ledger

Claim	Evidence type	Source / basis
GIA overall cut grades are currently for standard round brilliants, not fancy shapes	Primary-source fact	GIA fancy-shape cut grading FAQ
Polish and symmetry are separately reported grading characteristics	Primary-source fact	How GIA Grades Diamonds
1.00–1.05 L/W and the depth/table bands shown here are useful starting filters	Editorial screening ranges	AsscherDiamond.com methodology v1.1; final acceptance requires visual inspection

Last evidence review: September 6, 2026. If GIA changes the scope of its fancy-shape cut grading, this page should be reviewed before the screening framework is reused.