Chances are you’ve heard of the 4 Cs. A diamond’s cut, color, clarity, and carat weight all determine its value, but if there’s one characteristic that the general public pays the most attention to, it’s carat weight. Like its name implies, carat weight refers to the weight of a particular gemstone. One carat equals approximately 0.2 grams.

So how does carat weight translate to size? Below, we’ve listed some of the approximate sizes you can expect for certain diamond weights.

For round diamonds…

• 1 mm = 0.005 carat
• 1.5 mm = 0.015 carat
• 2 mm = 0.03 carat
• 2.5 mm = 0.06 carat
• 3 mm = 0.10 carat
• 3.5 mm = 0.16 carat
• 4.1 mm = 0.25 carat
• 4.6 mm = 0.38 carat
• 5.2 mm = 0.50 carat
• 5.6 mm = 0.65 carat
• 6 mm = 0.80 carat
• 6.4 mm = 1.00 carat
• 7 mm = 1.25 carat
• 7.5 mm = 1.60 carat
• 8 mm = 2.00 carat
• 8.6 mm = 2.50 carat
• 9.3 mm =3.00 carat
• 9.8 mm = 3.50 carat
• 10.2 mm = 4.00 carat
• 10.5 mm = 4.50 carat
• 11 mm = 5.00 carat

For square diamonds…

• 1.25 mm = 0.015 carat
• 1.5 mm = 0.025 carat
• 2 mm = 0.05 carat
• 2.5 mm = 0.09 carat
• 3 mm = 0.16 carat
• 3.5 mm = 0.25 carat
• 4 mm = 0.40 carat
• 4.5 mm = 0.50 carat
• 5 mm = 0.75 carat
• 5.5 mm = 1.00 carat
• 6.5 mm = 1.50 carat
• 7 mm = 2.00 carat
• 8 mm = 3.00 carat
• 9 mm = 4.00 carat
• 9.5 mm = 5.00 carat

For oval diamonds…

• 3 x 2.3 mm = 0.05 carat
• 3.6 x 2.7 mm = 0.10 carat
• 4 x 3 mm = 0.16 carat
• 4.5 x 3 mm = 0.20 carat
• 5 x 3 mm = 0.25 carat
• 5 x 4 mm = 0.33 carat
• 6 x 4 mm = 0.38 carat
• 6.25 x 4.5 mm = 0.50 carat
• 7 x 5 mm =0.75 carat
• 8 x 6 mm = 1.00 carat
• 9 x 6.5 mm = 1.50 carat
• 10 x 7 mm = 2.00 carat
• 11.5 x 8 mm = 3.00 carat
• 12.5 x 9 mm = 4.00 carat
• 13.6 x 10 mm 5.00 carat

For marquise diamonds…

• 2.5 x 1.25 mm = 0.025 carat
• 3 x 1.5 mm = 0.035 carat
• 3.5 x 1.75 mm = 0.05 carat
• 3.5 x 2 mm = 0.07 carat
• 4 x 2 mm = 0.08 carat
• 4.5 x 2.5 mm = 0.12 carat
• 5 x 2.5 mm = 0.15 carat
• 5 x 3 mm = 0.20 carat
• 6 x 3 mm = 0.25 carat
• 6 x 3.5 mm = 0.33 carat
• 8 x 4 mm = 0.50 carat
• 9 x 5 mm = 0.75 carat
• 10.5 x 5.5 = 1.00 carat
• 11.5 x 6 mm = 1.50 carat
• 12.5 x 6.5 mm = 2.00 carat
• 15 x 7.5 mm = 3.00 carat
• 15.5 x 8 mm = 4.00 carat
• 17.5 x 8.5 mm = 5.00 carat

For emerald cut diamonds…

• 3 x 2.3 mm = 0.10 carat
• 3.75 x 2.75 mm = 0.20 carat
• 4 x 3 mm = 0.25 carat
• 4.5 x 3 mm = 0.33 carat
• 5 x 3.5 mm = 0.40 carat
• 5.5 x 4 mm = 0.50 carat
• 6 x 4.5 mm = 0.75 carat
• 6.5 x 5 mm = 1.00 carat
• 7.5 x 5.5 mm = 1.50 carat
• 8.5 x 6 mm = 2.00 carat
• 9.5 x 7 mm = 3.00 carat
• 10.5 x 8 mm = 4.00 carat
• 11.5 x 8.5 mm = 5.00 carat

For pear diamonds…

• 3 x 2 mm = 0.05 carat
• 4 x 2.5 mm = 0.11 carat
• 4.5 x 3 mm = 0.16 carat
• 5 x 3 mm = 0.20 carat
• 5.5 x 3.5 mm = 0.25 carat
• 6 x 4 mm = 0.33 carat
• 7 x 5 mm = 0.50 carat
• 7.5 x 5.25 mm = 0.75 carat
• 8.5 x 5.5 mm = 1.00 carat
• 9.5 x 6.5 mm = 1.50 carat
• 11 x 7 mm = 2.00 carat
• 12.5 x 8 mm = 3.00 carat
• 13.5 x 9 mm = 4.00 carat
• 15 x 9.5 mm = 5.00 carat

For trillion diamonds…

• 2.5 mm = 0.05 carat
• 3 mm = 0.09 carat
• 3.5 mm = 0.12 carat
• 4 mm = 0.18 carat
• 4.5 mm = 0.23 carat
• 5 mm = 0.33 carat
• 5.5 mm = 0.40 carat
• 6 mm =0.50 carat
• 7 mm = 0.75 carat
• 8 mm = 1.00 carat
• 9 mm = 1.50 carat
• 10 mm = 2.00 carat

For Asscher diamonds…

• 2 mm = 0.05 carat
• 2.6 mm = 0.10 carat
• 3 mm = 0.16 carat
• 3.5 mm = 0.25 carat
• 4 mm = 0.33 carat
• 4.5 mm = 0.50 carat
• 5 mm = 0.75 carat
• 5.5 mm = 1.00 carat
• 6.25 mm = 1.50 carat
• 7 mm = 2.00 carat
• 8 mm = 3.00 carat
• 8.5 mm = 4.00 carat
• 9.5 mm = 5.00 carat

For cushion cut diamonds…

• 3 mm = 0.16 carat
• 3.6 mm = 0.25 carat
• 4.5 mm = 0.50 carat
• 5.25 mm = 0.75 carat
• 6 mm = 1.25 carat
• 6.5 mm = 1.50 carat
• 7 mm = 2.00 carat
• 8.2 mm = 3.00 carat
• 8.7 mm = 4.00 carat
• 9.7 mm = 5.00 carat

It’s important to note that these are approximations for diamond size based on carat weight (and vice versa). Every diamond is individually cut, meaning that each one is unique. Two diamonds having the same carat weight may measure differently depending on how they’re cut. That’s just one of the reasons why it’s prudent to work with a diamond buying expert when looking to purchase your own diamond. They’ll be able to make sure the diamond you select was cut properly and has a size worth its carat weight.