---
title: "Average diameter: meaning in gemology"
description: "The average diameter of a round is the mean of its minimum and maximum diameters, measured across the girdle."
url: https://digitalgemology.com/learn/glossary/average-diameter
image: https://digitalgemology.com/img/og-digital-gemology.png?v=d224fb01
---

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[Glossary](https://digitalgemology.com/learn/glossary) · Anatomy and proportions

# Average diameter

Also called mean diameter

The average diameter of a round is the mean of its minimum and maximum diameters, measured across the girdle.

## In more detail

It is the base for the percentages on a report. Table, crown height, girdle, pavilion depth and total depth are all shares of it.

## On a grading report

Not printed as its own line: average the first two numbers of the measurements line.

## Related terms

- [Measurements](https://digitalgemology.com/learn/glossary/measurements): Measurements is the report line that gives a stone's size in millimeters. A round reads minimum – maximum diameter × depth, and a fancy shape length × width × depth.
- [Total depth](https://digitalgemology.com/learn/glossary/total-depth): Total depth is the height of a stone from table to culet as a percentage of its average diameter. It equals crown height + girdle thickness + pavilion depth.
- [Table size](https://digitalgemology.com/learn/glossary/table-size): Table size is the width of the table as a percentage of the average diameter.
- [Proportions](https://digitalgemology.com/learn/glossary/proportions): A diamond's proportions are the angles and percentages that describe its shape in profile. They cover the table, crown, pavilion, star and lower half lengths, girdle, culet and total depth.

## Learn more

- [Diamond measurements explained: diameter, depth and percentages](https://digitalgemology.com/learn/diamond-anatomy/diamond-measurements-explained)

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