---
title: "Cut Performance Index: meaning in gemology"
description: "The Cut Performance Index is Digital Gemology's open table of light-performance scores for the cuts we sell, in seven gemstones. It gives each cut…"
url: https://digitalgemology.com/learn/glossary/cut-performance-index
image: https://digitalgemology.com/img/og-digital-gemology.png?v=d224fb01
---

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[Glossary](https://digitalgemology.com/learn/glossary) · How we measure

# Cut Performance Index

Also called CPI, Digital Gemology Cut Performance Index

The Cut Performance Index is Digital Gemology's open table of light-performance scores for the cuts we sell, in seven gemstones. It gives each cut brilliance, fire, scintillation, tilt, symmetry, spread, shape-norm, leakage and an overall score.

## In more detail

Each gemstone has its own table, because the same cut handles light differently in each stone. Compare cuts within one gemstone only, never across stones. Ruby and sapphire share one refractive index in the engine, so their figures are the same. The scores describe the design of a cut, not a real stone.

## How we measure it

Our light census computes the scores, with the same code as the Cut Performance Wheel and the cut pages. On 31 October 2026 it scored 37 of our 40 cuts. The heart and two cuts with no table are not scored yet, nor are the five Platonic solids. The data is free under CC BY 4.0, as CSV and JSON, and archived on Zenodo (DOI 10.5281/zenodo.23844870).

## Related terms

- [Light census](https://digitalgemology.com/learn/glossary/light-census): The light census is our ray tracer behind the Cut Performance Wheel, the cut-page scores and the Cut Performance Index. It drops a fixed set of rays on a stone from above and counts where each one leaves.
- [Overall score](https://digitalgemology.com/learn/glossary/overall-score): The overall score is one figure out of 100 that combines our light-performance scores for one cut in one gemstone. The Cut Performance Wheel calls it Global.
- [Cut Performance Wheel](https://digitalgemology.com/learn/glossary/cut-performance-wheel): The Cut Performance Wheel is a free Digital Gemology tool. It draws eight light-performance scores of one cut, in one gemstone, on a wheel.
- [Brilliance](https://digitalgemology.com/learn/glossary/brilliance): Brilliance is the white light that a cut stone returns to the viewer. In our census, it is the share of entering light that leaves through the crown toward the viewer.
- [Fire](https://digitalgemology.com/learn/glossary/fire): Fire is the flashes of spectral color that a cut stone sends out. In our census, fire is the share of returned light whose colors leave more than 0.6° apart.
- [Fixed settings](https://digitalgemology.com/learn/glossary/fixed-settings): Fixed settings are the constants of our scoring method that we chose rather than measured. They are the same for every cut, so the scores can rank cuts within one gemstone.

## Learn more

- [Digital Gemology Cut Performance Index](https://digitalgemology.com/learn/cut-performance-index)
- [Cut Performance Wheel and cut-page scores](https://digitalgemology.com/about/how-we-measure/performance-wheel)

[All 328 terms](https://digitalgemology.com/learn/glossary)