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The Dead-Simple Guide to Carat Weight

By Lead Gemologist Erica Hirsch, GIA GG

Carat weight can be misleading.

Picture a trusty, yellow, #2 pencil.  That’s the one. It has a round, pink eraser on top that’s 7mm in diameter. 7mm is also the diameter of a 1.25 carat round brilliant diamond.

That might be more or less diamond than you expected. That’s partly because we price diamonds by carat weight, not their dimensions. The size a diamond appears is determined by both its carat and its shape. Diamonds of the same weight, but in different shapes, will appear to be different sizes.

When choosing a diamond shape, you might end up with a much larger, or smaller diamond than you were expecting.

As an example, a .7 carat oval diamond can look as large as a 2 carat Asscher diamond.

With your little pink friend as your guide, explore how the other cuts and shapes stack up in size and cost and of course, carat weight.  

Ways to remove wasted carat weight:

A diagram showing a diamond with an extremely thick girdle.

Avoid “very” and “extremely” thick or thin girdles.

Avoid excess weight in the bottom of stones.

A diagram depicting a diamonds overall measurements.

Use dimensions to understand size.