How do you grade a diamond?

Answer 1

A diamond is valued by its cut, clarity, carat weight and colour. A local jeweler educate you on these grades.

Add'l info: You can't grade a diamond yourself and a jeweler, while knowledgeable, can't give you a reliable grade either. You have to send the stone to a grading organization. There are many but the gold standard is generally considered to be GIA (gemology institute of america). They developed the 4Cs grading system that the above answer mentions and that all the other grading orgs use as well.

Answer 2

A diamond is graded based on its cut, colour, clarity and carat.
Color - most people believe diamonds to be clear or colorless, the majority of diamonds are yellow, brown, and black. The rarest of all diamond colors are white (or colorless). The Gemological Institute of America (G.I.A.) grades color alphabetically from D (totally colorless) to Z (yellow). For a diamond to be considered “colorless,” the G.I.A. requires that it be a D, E, or F. However, the D-Z scale is continuous, so the difference between an F and G is very small. The average color for engagement diamonds in the retails industry is G to H.

Carat weight - a carat is actually a standard unit of measure that defines the weight of a diamond. One carat is equivalent to 200 milligrams. Carat sizes are also expressed as “points”, with a one carat diamond equaling 100 points, a one-half carat diamond being 50 points, a three-quarter carat diamond being 75 points, and so on.

Clarity - A diamond’s clarity refers to the presence of identifying characteristics on and within the diamond. Diamonds are graded for clarity under 10x loupe magnification. Clarity grades range from Internally Flawless, diamonds, which are completely free of blemishes and inclusions even under 10 x magnifications, to Imperfect 3, diamonds which possess large, heavy blemishes and inclusions that are visible to the naked eye.

Cut – that’s a reference to the diamond’s reflective qualities, not the shape. Diamond cut is perhaps the most important of the four Cs, so it is important to understand how this quality affects the properties and values of a diamond. A good cut gives a diamond its brilliance, which is that brightness that seems to come from the very heart of a diamond. The angles and finish of any diamond are what determine its ability to handle light, which leads to fire, brilliance & scintillation.