Carat weight vs. diameter of a diamond

UPDATED:

How do carat and measurements relate? Or: How big is a 1 carat round diamond?

Carat: The weight of a diamond

Despite what many people think, “carat” is not a measurement unit for the size (as in diameter), but the weight of a diamond. One carat corresponds to 0.2 grams, which is roughly the weight of the eponymous carob seed: Because these seeds didn’t differ much in weight, they were used by early gem traders as counterweights in their balance scales. In 1913, the standard of a carat weighing 0.2 was established in the US and soon adopted all over the world. Carat is not to be confused with karat, which refers to the purity of gold.

The size of diamonds

The diamond certificates issued by the GIA contain information on the measurements of a diamond. We have created an overview of how big the diameter of diamonds in certain shapes and carat sizes usually is. Please note that the exact measurements of a certain diamond might differ!

Round

Carat-weight

Length

Width

0.25 ct

4.1 mm

4.1 mm

0.50 ct

5.2 mm

5.2 mm

0.75 ct

5.8 mm

5.8 mm

1.00 ct

6.5 mm

6.5 mm

1.50 ct

7.4 mm

7.4 mm

2.00 ct

8.2 mm

8.2 mm

5.00 ct

11.1 mm

11.1 mm

Oval

Carat-weight

Length

Width

0.25 ct

5.0 mm

3.0 mm

0.50 ct

6.0 mm

4.0 mm

0.75 ct

7.0 mm

5.0 mm

1.00 ct

7.5 mm

5.5 mm

1.50 ct

8.5 mm

6.5 mm

2.00 ct

9.0 mm

7.0 mm

5.00 ct

13.9 mm

9.3 mm

Princess (here: square)

Carat-weight

Length

Width

0.25 ct

3.4 mm

3.4 mm

0.50 ct

4.4 mm

4.4 mm

0.75 ct

5.1 mm

5.1 mm

1.00 ct

5.5 mm

5.5 mm

1.50 ct

6.5 mm

6.5 mm

2.00 ct

7.5 mm

7.5 mm

5.00 ct

9.4 mm

9.4 mm

Pear

Carat-weight

Length

Width

0.25 ct

4.5 mm

3.0 mm

0.50 ct

6.0 mm

4.0 mm

0.75 ct

7.5 mm

5.0 mm

1.0 ct

8.4 mm

5.6 mm

1.50 ct

9.0 mm

6.0 mm

2.00 ct

10 mm

6.67 mm

5.00 ct

12.4 mm

8.5 mm

Radiant (here: rectangular)

Carat-weigh

Length

Width

0.25 ct

4.3 mm

3.2 mm

0.50 ct

5.6 mm

4.2 mm

0.75 ct

6.2 mm

4.7 mm

1.00 ct

6.9 mm

5.2 mm

1.5 ct

7.5 mm

5.7 mm

2.00 ct

8.3 mm

6.2 mm

5.00 ct

11.2 mm

9.1 mm

Emerald

Carat-weight

Length

Width

0.25 ct

5.0 mm

3.3 mm

0.50 ct

6.0 mm

4.0 mm

0.75 ct

6.5 mm

4.3 mm

1.00 ct

6.9 mm

4.6 mm

1.50 ct

8.1 mm

5.4 mm

2.00 ct

8.7 mm

5.8 mm

5.00 ct

11.4 mm

8.5 mm

Careful: The measurements in the tables serve for orientation only. You can look up the exact measurements of a diamond in its certificate.

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