These pages name every part of a round brilliant and explain every proportion on a grading report: table, crown, pavilion, star and lower half lengths, girdle and culet. Each page uses our free Cut Grading Tool, 3D Gemstone Simulator or Hearts & Arrows Scope, so you can change one proportion and see what it does to the light and the grade. The last page puts it all together and decodes a stone from its numbers.
New here? Start with Pavilion angle and pavilion depth: how a diamond keeps the light in.
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1 · Video
The parts of a diamond: crown, girdle and pavilion
Crown, girdle and pavilion, the 57 facets of a round brilliant by name, and what each part does with light.
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2 · Article
Diamond measurements explained: diameter, depth and percentages
Read the measurements line, work out the total depth, and see how crown height, girdle and pavilion depth add up.
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3 · Video
Diamond table percentage: what table size does to the light
How table size is measured, what a bigger table does to the crown and the grade, and why bigger is not brighter.
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4 · Video
Crown angle and crown height in a round diamond
What the crown angle does with light, how it sets the crown height, and how a steeper pavilion can rescue a shallow crown.
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5 · Animated explainer
Pavilion angle and pavilion depth: how a diamond keeps the light in
How the pavilion keeps the light in, what too shallow and too steep look like, and the narrow Excellent window.
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6 · Video
Star length and lower half length in a round brilliant
What star and lower half lengths measure, how they shape the pattern and the hearts, and what painting and digging cost.
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7 · Article
Diamond girdle thickness: thin, medium, thick and what it costs you
How a girdle is described, the trade between durability and hidden weight, and the thicknesses that keep a round Excellent.
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8 · Article
The diamond culet: none, pointed or large
What the culet is for, its eight sizes, how a large one shows face up, and how much it can cost a grade.
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9 · Article
How to read diamond proportions: decode a stone from its numbers
A six-step routine to read a full set of proportions, predict the cut grade and find the one number that limits it.
Quick quiz
Every lesson ends with a few questions. Want more? The Anatomy of a diamond quiz covers the whole topic, with the answer and the reason after each question.
Cuts in this topic
We sell the files of these cuts: 3D models and cutting files, with a personal-use license.
