Your cart

Your cart is empty

How do I measure a diamond? Find the size of your diamond

How do I measure a diamond? Find the size of your diamond

Measuring your diamond

Something that causes confusion for many people is the size of the diamond, with most thinking that the size of a diamond refers to its carat. However, this is not the case, size is determined by the physical size of the diamond in millimeters and the carat is measured by its weight.

To help you along the way, I will show you methods you can use to measure your diamond effectively with inexpensive methods.

Professional Diamond Measuring Tools

Diamond size is usually measured, in the jewellery industry, using the tools shown below. Once measurements are noted, a formulae is then used to determine the carat size. 

Presidium Diamond Gauge (PDG)

This nifty tool is used by diamond professionals and those in the diamond/jewellery industry. Available in either dialog or analogue form, this tool can measure diamonds as well as gemstones effectively, from 0.0mm all the way to 23.0mm. With this method the diamond that requires measuring will need to be dismounted from its setting for the most accurate reading.

presidium diamond gauge


Vernier Caliper

This tool is very useful not only in the Diamond/ Jewellery industries but in many other industries too. With two scales it has the ability to measure internal and external dimensions effectively and can measure up to one-hundredth of a millimeter. This tool can also be found with an analogue or digital reader for more accuracy.

vernier caliper


Ways to measure your diamond at home

The tools mentioned above are not your everyday tools and will cost a fortune to buy for personal use, however there are alternative ways to measure your diamond at home too. Although the tools below will not be able to give you an exact size, they will however give you an estimated size of your diamond.

Carat Size Charts

This method is a chart where most diamond shapes are displayed in different sizes, that also includes their carat. However using a chart to determine the size of your diamond will not give you an accurate measurement, only an estimate. Usually in the form of a leaflet, you would simply line your diamond up against the closest fit. That would then be the estimated size of your diamond.

Diamond and Gemstone Measuring Gauge

This piece of equipment looks a fan, found either in metal or plastic. Each level will have multiple holes where you would then try and feed your diamond through. The one that fits the closest to your diamond without force would be your estimated diamonds size. You can find this item online for a low cost.

Diamond Certificate

Upon purchasing your diamond, you may have received a certificate which will have the size of your diamond displayed under measurements. If there are different measurements displayed this will be because most diamonds vary fractionally in size, as a result the smallest and largest readings may also be stated.

Using formulae to calculate your diamonds size?

Once measured, there will be different formulae to note for all different shape/cut diamonds because you cannot measure a round diamond the same way you would a baguette cut diamond. Whilst length and width are taken initially its also important to find out the depth of a diamond to be able to work out its carat. Below are two examples of this.

Round Brilliant Cut Diamonds = Diameter x Depth 

Emerald/ Cushion/ Baguette Cut Diamonds etc. = Length x Width x Depth

Once one of the above formulae is completed correctly you will finally have the carat of your diamond. 

Final Thought

Measuring your diamond doesn’t need to be a daunting task, however, be very careful if your diamond is not mounted when you are measuring them as they are very bouncy and in no time at all can be lost quickly and sometimes even end up at the other side of the room without your knowledge. Here at Sonny’s we don’t suggest or recommend you unmount your diamond from its mount yourself, you could damage the piece of jewellery in which it sits or loose your diamond. If you have any other queries or would like us to measure your diamonds please feel free to contact us and book an appointment.

Back to Sonny's Jewellery Blog