How to Read a Diamond Certificate Step by Step

Open a diamond grading report and you will see boxes, numbers and a small diagram. It looks technical, but it follows a fixed pattern. Take it one section at a time.

1. The report number and date

At the top you will find the report number, the date and the laboratory's name. The number is how you verify the report on the laboratory's website. Make sure it matches the number on the invoice.

2. Shape and cutting style

This states the shape, such as round, oval, pear or emerald, and the cutting style, such as brilliant or step cut. It tells you how the facets are arranged. For the most common shapes, see diamond shapes guide.

3. Measurements

The report gives dimensions in millimetres. For a round stone these are the minimum and maximum diameter and the depth. Measurements tell you how big the stone looks from above, which does not always match its weight. See carat weight versus diamond size.

4. Carat weight

One carat is 0.2 gram. Weight is stated to the hundredth of a carat, so a stone of 0.50 carat and one of 0.49 carat are close in size but can be priced differently.

5. Colour grade

Colour is graded on a scale from D, which is colourless, through to Z, which is light yellow or brown. D to F are colourless, G to J are near colourless. See diamond colour grades D to Z explained.

6. Clarity grade

Clarity describes internal features and surface marks, from Flawless through Included. The report may include a plot, a diagram of the stone showing the position of notable features. See diamond clarity: VS, SI and VVS.

7. Cut grade

For standard round brilliant stones, the report may give a cut grade such as Excellent or Very Good. It reflects proportions and how well the stone returns light. See diamond cut grades explained.

8. Polish and symmetry

These grade the finish of the surface and the exactness of the facet shapes. Excellent and Very Good are common. See diamond polish and symmetry explained.

9. Fluorescence

This shows how the stone reacts under ultraviolet light, from none to very strong. See diamond fluorescence explained.

10. Comments and inscription

The comments section can note the stone's features, such as whether it has been laser-inscribed. If the report number is inscribed on the girdle, this will be noted.

11. The proportion diagram

Some reports show a side-view diagram with percentages for depth, table and other proportions. These help specialists judge cut, but as a buyer, the cut grade and your own eyes tell you most of what you need.

A reading routine

1. Match the report number and the stone's details with the invoice.
2. Check that carat, colour and clarity on the report match what you were quoted.
3. Look at the cut, polish and symmetry for round stones.
4. Check the fluorescence and comments.
5. Verify the report online.

Getting help

If anything is unclear, ask the jeweller to explain it in front of the stone. We are glad to do this at our showroom: book an appointment. You can also see how certified stones are described in our diamond pendants.