Holloway Cut Adviser (HCA)
Holloway Cut Adviser (HCA)
A proportion-based tool for preliminary diamond cut assessment
The Holloway Cut Adviser (HCA) is a free, publicly accessible online calculator developed by Australian diamond industry researcher Garry Holloway for evaluating the predicted light performance of a round brilliant-cut diamond from its four key proportion measurements: table percentage, depth percentage, crown angle, and pavilion angle. Despite the common abbreviation sometimes rendered as "GIA Holloway Cut Adviser" in trade conversation, the tool has no affiliation with the Gemological Institute of America; the association arises informally because users frequently apply it alongside GIA grading reports, whose proportion data serve as the primary input.
How It Works
The HCA translates proportion data into a composite numerical score intended to reflect four optical attributes: light return, fire, scintillation, and spread (the visual diameter of the stone relative to its carat weight). These sub-scores are weighted and combined into a single figure. The scoring scale is inverse — lower numbers indicate superior predicted performance:
- 0–2: Excellent — recommended for further consideration
- 2–4: Very Good to Good
- 4–6: Fair
- 6 and above: Poor
A score below 2.0 is widely cited as the threshold at which a stone merits serious visual inspection. Conversely, a score above 4.0 is generally taken as a signal that the proportions are likely to compromise brilliance or fire in a meaningful way, and many experienced buyers use that threshold as a preliminary filter when reviewing large inventories online.
Scope and Limitations
The HCA is explicitly a screening tool, not a grading instrument. It operates on four proportion variables and therefore cannot account for the full optical complexity of a finished diamond, which is also influenced by facet-shape precision, symmetry, polish quality, lower-girdle facet length, star facet length, girdle thickness variation, and culet size. Two diamonds with identical HCA inputs can perform very differently in person if their facet geometry diverges in ways the four-variable model does not capture.
Holloway himself has consistently described the tool as a means of eliminating clearly inferior cuts from consideration rather than of identifying the single best stone. It does not replace light-performance imaging systems such as ASET (Angular Spectrum Evaluation Tool), Ideal-Scope, or the ray-tracing analyses offered by laboratories and specialist vendors. Formal cut grades issued by GIA, AGS Laboratories, or other accredited bodies involve far more comprehensive proportion and symmetry analysis.
The HCA is also calibrated specifically for the standard round brilliant cut. It is not applicable to fancy shapes — ovals, cushions, pears, princess cuts, and similar outlines — whose optical behaviour depends on proportion relationships that differ fundamentally from the round brilliant model.
Place in the Trade
Since its introduction in the early 2000s, the HCA has become a standard first-pass filter among online diamond buyers and trade professionals reviewing large virtual inventories. Its value lies precisely in its accessibility: a buyer with a GIA grading report in hand can enter four numbers and obtain an immediate, consistent indication of whether a stone's proportions fall within a broadly accepted performance window. This has contributed to a measurable shift in the market toward tighter proportion ranges, as stones scoring poorly become harder to sell to an informed buyer base.
It is worth noting that the HCA represents one school of thought regarding optimal round brilliant proportions — broadly aligned with the "Tolkowsky ideal" tradition — and that other credible analytical frameworks weight the trade-offs between brilliance, fire, and scintillation differently. A stone that scores modestly on the HCA may still be visually compelling under certain lighting conditions or to a buyer who prioritises fire over light return.