Research & evidence

Asscher Size & Millimeter Reference

A transparent carat-to-millimeter planning reference

Updated: September 6, 2026ResearchMethodology disclosed

What this dataset is

This is a planning reference for approximate face-up width by Asscher carat weight. It is not a laboratory standard and it is not presented as a measured population average. Individual stones can fall outside these bands because carat is weight—not face-up size—and proportion sets differ.

Reference status: Version 1.0 · values unchanged after September 6, 2026 review · six carat bands · editorial planning ranges · downloadable CSV. These are not measured population medians.

Asscher face-up width reference

Carat	Approx. width range	Midpoint for planning	Status
0.50 ct	4.2–4.6 mm	4.4 mm	Reference range
0.75 ct	4.8–5.2 mm	5.0 mm	Reference range
1.00 ct	5.3–5.7 mm	5.5 mm	Reference range
1.50 ct	6.0–6.4 mm	6.2 mm	Reference range
2.00 ct	6.6–7.1 mm	6.85 mm	Reference range
3.00 ct	7.5–8.1 mm	7.8 mm	Reference range

Download the CSV dataset

Provenance and limitations

The ranges consolidate the planning values already used in the site’s size guides. They are intentionally labeled reference ranges because the initial editorial edition did not preserve a large raw inventory sample that would justify calling them observed medians or percentiles. Future revisions should only upgrade the evidence label if a reproducible sample is retained.

Why width varies at the same carat

GIA defines one metric carat as 200 milligrams. That means two diamonds can have equal carat weight while distributing that mass differently. A deeper Asscher can retain more weight below the girdle and therefore present a smaller face-up width than a more efficiently spread stone of the same weight.

How to use the reference responsibly

Use width as a comparison tool, not a quality grade.
Check both length and width on the actual grading report.
Compare stones within the same carat neighborhood before assuming one is “large” or “small.”
Do not infer light performance from millimeters alone.

Primary reference

GIA 4Cs: Diamond Carat Weight — carat measures weight; one metric carat equals 200 mg.
Asscher Carat Size Chart
Asscher Dimensions in Millimeters

How to reproduce the comparison

Take length and width from the candidate’s grading report.
Use the published CSV only as an approximate carat-neighborhood reference.
Compare candidates at similar carat weights using their real millimeters.
For a rough relative face-up comparison, multiply length × width. This is a footprint proxy, not a cut grade or exact visible-area calculation.
Inspect the actual diamond for windowing, extinction and pattern before preferring the wider stone.

Provenance: the six ranges are retained from the site’s original editorial planning tables. Because the original edition did not preserve a raw inventory sample, the values remain labeled editorial reference ranges. The September 2026 review changed the documentation, not the numbers.

Version record

Version	Date	Change
1.0	August 23, 2026	Initial six-band editorial planning reference
1.0 review	September 6, 2026	Values unchanged; provenance, comparison method and evidence labeling clarified