The 4 C's of Diamonds - Carat

Diamond carat refers to a stone’s weight, not just its size. Our guide explains what carat really means, how it affects appearance and value, and how to choose the right...

Updated on February 18, 2026 by Alison Skeates

Diamond carat refers to the weight of a diamond, rather than its physical size - though the two are closely related.

Historically, the term carat comes from the carob seed, which was once used as a unit of measurement due to its perceived consistency in size and weight. While charming, it wasn’t especially precise.

Today, diamond carat is a standardised metric measurement.

One metric carat is defined as 200 milligrams.

Diamonds are also measured in points, where:

> 1 carat (1.00ct) = 100 points

> 0.50ct = 50 points

> 0.25ct = 25 points

This system allows for accurate comparison between stones.

DOES A HIGHER CARAT MEAN A BIGGER DIAMOND?

Not always.

While a higher carat weight generally means a larger diamond, cut quality plays a huge role in how large a diamond appears. A well-cut diamond can look noticeably bigger than a heavier stone with poor proportions.

For example, two diamonds with the same carat weight may appear very different in size depending on:

>Their cut proportions

> Depth and table size

> Shape (oval, round, emerald cut, etc.)

This is why we always consider carat alongside Cut, Colour and Carat - the full picture matters.

CARAT, RARITY AND VALUE

As carat weight increases, diamonds become rarer, and their value rises accordingly - especially when combined with high colour and clarity grades.

However, value doesn’t increase in a straight line. Certain weights (such as 1.00ct) carry a premium simply because of demand. Choosing a diamond just under these thresholds can often offer better value without a visible difference in size.