Diamond Buyers Guide

Diamond Carat Weight

How diamonds are measured — and why bigger isn't always better.

A diamond's carat weight measures how much it weighs, not how large it appears. One carat equals 200 milligrams (0.2 grams) — roughly the weight of a small paper clip. The word "carat" comes from the carob seed, which ancient gem traders used as a counterweight because of its remarkably consistent weight.

Each carat is divided into 100 points, allowing precise measurement to the hundredth decimal place. A 0.75-carat diamond is described as a "seventy-five pointer" or "three-quarter carat."

Carat Weight vs. Visual Size

Two diamonds of equal carat weight can appear quite different in size depending on their cut proportions and shape:

• A deeply cut diamond carries more weight in its depth, so it looks smaller face-up than its carat weight suggests.
• A shallow-cut diamond spreads weight across a wider table, looking larger face-up — but at the cost of brilliance.
• Elongated shapes (oval, marquise, pear) have a larger surface area per carat than round diamonds, making them appear bigger for the same weight.

Size Comparison

These approximate face-up diameters (for well-cut round diamonds) give you a sense of how carat weight translates to visual size:

How Carat Weight Affects Price

Diamond prices don't increase linearly with carat weight — they increase exponentially. This is because larger rough diamonds are significantly rarer than smaller ones. A 2-carat diamond doesn't cost twice as much as a 1-carat diamond of equal quality; it costs considerably more.

Prices also jump at popular "magic sizes" — whole and half-carat marks where demand spikes:

A 0.98ct diamond may look identical to a 1.00ct diamond face-up but cost 10–20% less because it falls below the magic 1-carat threshold.

Tips for Getting the Best Value

• Buy just below magic sizes: A 0.90ct or 1.90ct diamond can save thousands while looking virtually identical to a full carat or two carats.
• Prioritize cut: A smaller diamond with an Excellent cut will appear larger and more brilliant than a bigger stone with a Poor cut.
• Consider shape: An oval, marquise, or pear shape will look noticeably larger than a round diamond of the same carat weight because of their elongated face-up area.
• Total carat weight: In multi-stone settings like diamond stud earrings and diamond tennis bracelets, carat weight refers to the combined weight of all diamonds. "1 carat total weight" (1 ctw) means the total of all stones.