First off… Welcome to Wedding Bee, and “the Hive”
My best advice, is that I suggest that you do some reading up on Diamonds if you are in the market for one. A good place to start is just plain old Wikipedia
Wikipedia – Diamond (Gemstone) = http://en.wikipedia.org/wiki/Diamond_(gemstone)
Beyond that there are some great entries on Diamond Websites like Blue Nile
Blue Nile – Diamond Education = http://www.bluenile.ca/diamonds/diamond-education
You will find out that Diamonds come a wide variety of cuts and qualities… there really is something for everyone’s budget… just depends on what that is and what you consider to be the most important of the 4Cs for you (actually there are 5 Cs if you count Certification)
Cut (Shape AND Quality) – Colour – Clarity – Carat (size) – and Certification
For the most sparkly of diamonds, you want to put the emphasis on Cut & Colour. Followed by Clarity, Carat Size, and Certification dependent on your own interests and budget.
Cut (Shape) will determine the actual size of the diamond.
For example a 1/2 Carat = 0.50 Stone will vary dependent on which shape you choose…
Here then a chart that will help to explain that for you…
The page that it takes you to is for IDEAL CUT Round Brilliants… if you click on the various shapes (list along the side) you’ll see the differences in size for each shape.
A .50 Carat Round would be 5.2 mm diameter, while a .50 Carat Princess (square) would be 4.4 mm x 4.4 mm…
Remember though that these are IDEAL CUTS (the highest quality) so… size will be different if the cut is less than perfect (both the part you see… the surface / face of the diamond, and the part underneath)
Again, you need to read up to fully understand what is out there, and to make sure you KNOW fully what you are getting when you (or your Fiance) makes this important purchase
Hope this helps,
EDIT TO ADD… The Inclusions in an I Quality Diamond (I1 to I3) are those that can be typically seen with a naked eye. The standard is that they must be visible at less than 10x magnification. Inclusions in a S1 or S2 Diamond, are only visible at 10x magnification, and are rarely visible to the naked eye. Inclusions in a VS1 or VS2 Diamond are only visible with magnfication… and may even then be difficult to see. A Dimond that is rated at IF has no Inclusions that can be seen under 10x magnification, and maybe a few blemishes on the surface of the diamond itself. A Diamond that is FL is as close to flawless as you can get… with no inclusions or blemishes that can be easily seen even at 10x magnification.