Understanding Round Diamond Sizes

When shopping for a diamond, most people focus on carat. But what many don’t realize is that carat refers to weight, not size. The actual diameter or size in millimeters can vary based on the shape and cut of the diamond. In this post, we’ll break down the typical measurements of 1-carat, 2-carat, and 3-carat round diamonds, and explain how they compare in both look and feel.

What Is a Carat?

The word “carat” is a unit of weight, not size.

• 1 carat = 0.2 grams

Carat weight affects the price and value of a diamond, but it doesn’t tell you how large the diamond will look. That’s why it helps to also understand millimeter measurements, especially if you’re trying to visualize the diamond on a hand.

1-Carat Diamond Engagement Ring

• Weight: 1.00 carat = 0.2 grams

• Average diameter: 6.4 mm to 6.5 mm

A 1-carat round diamond is one of the most popular choices. It has a balanced and elegant appearance and works well for solitaire rings or classic engagement designs.

While the weight is 0.2 grams, the diamond face (what you see from the top) measures about 6.5 mm across if it’s well cut.

2-Carat Diamond Engagement Ring

• Weight: 2.00 carats = 0.4 grams

• Average diameter: 8.1 mm to 8.2 mm

A 2-carat round diamond weighs twice as much as a 1-carat diamond, but it doesn’t appear twice as large. That’s because the diameter increases more slowly than the weight. On the other hand, the 2-carat diamond still looks significantly larger and attracts more attention. It’s a favorite for those who want something more eye-catching while still keeping a sense of balance.

3-Carat Diamond Engagement Ring

• Weight: 3.00 carats = 0.6 grams

• Average diameter: 9.1 mm to 9.4 mm

A 3-carat diamond has serious presence. It weighs 0.6 grams, three times more than a 1-carat diamond, and measures about 9.3 mm across. That gives it nearly double the face-up area of a 1-carat diamond. It’s a luxury choice and works best in bold designs or larger hands where the diamond has space to shine.

Key Notes to Remember

When choosing a diamond, it's important to know that a bigger carat weight doesn't always mean a much bigger-looking diamond. The way the diamond is cut plays a big role in how large it looks.

A well-cut 1-carat diamond can appear bigger than a poorly cut 1.5-carat diamond. The shape also makes a difference, shapes like oval or pear often look larger than round ones of the same weight.

Carat is measured in weight, and knowing how many grams a diamond weighs helps give a clearer picture. For example, a 3-carat diamond weighs only 0.6 grams, but it looks much larger than a 1-carat diamond because it has more surface area.

Lastly, as the carat size goes up, the price goes up a lot more. A 3-carat diamond isn’t just three times more expensive than a 1-carat diamond.

While carat weight gives a general idea of how large a diamond might be, it doesn’t always reflect the actual size. Cut quality diamond shape can greatly influence how big a diamond appears. For example, a well-cut 1-carat diamond may look larger than a poorly cut 1.5-carat diamond. It’s also important to note that as carat weight increases, the price rises significantly, often more than double or triple