How to Measure a Diamond | How to Find the Size of Your Diamond

Measuring the size of a diamond

How to measure a diamond?

Just how do you measure a diamond? Today we’re helping you to find out the size of your diamond.

An accurate diamond measurement is essential when choosing the correct engagement ring or jewellery setting. We’ll explain the best way to measure your diamond and the measurements needed for your jeweller.

Don’t confuse diamond carat weight with measurement

Size refers to the mm. measurement of a diamond. Carat weight relates, but does not refer to the size of the stone. Understandably, as carat weight increases, size increases.

Diamond measurement tools

The Presidium diamond gauge enables you to take an accurate diameter and depth for your diamond. The diameter is essential to determine the mm. size of the setting or ring mount for your diamond.

 

The Presidium diamond gauge

 

Buy the Presidium Gauge in our shop

Diamond measurement Presidium gauge

The best instrument for measuring your diamond is the Presidium gauge. We suggest using the analogue version. This diamond measurement instrument gives an accurate reading of the millimetre size of your diamond.

Using the diamond measurement gauge

 

How to find out diamond size without using a gauge

It is impossible to determine an accurate millimetre size without instrumentation. If you know your diamond shape and carat weight, it is possible to estimate a size typical for a well-proportioned diamond.

View the chart online

Diamond Size Chart - Millimetre Sizes for Diamonds

Reading the measurement from your diamond certificate

If you already have a diamond certificate, the diamond size will be recorded on your report. Look under ‘measurements’ for the size. For round brilliant cuts, two measurements are taken for the diameter—these are the maximum and minimum diameter measurements.

Replacement GIA certificate

Measuring small diamonds

Small diamonds are often supplied in regular millimetre sizes. For many items of jewellery, it is important to measure diamonds accurately to ensure they fit into their settings, matching for size and not just colour and clarity. Diamonds for eternity rings are just one example of accurately measured diamonds.

Diamond sizes for an eternity ring

How to measure a diamond. A guide to measuring the size of your diamond

The question – how to measure a diamond comes from newcomers to the jewellery industry and members of the public, but why would it be necessary to find out the measurements of a diamond?

Why measure a diamond?

There are various reasons why we would want to find out a diamond’s measurements. The most obvious is to match the diamond to the most appropriate ring setting. When we supply a finished ring mount for clients having an existing diamond, we need the full measurements to make up the suitable setting size. For example, a diamond weighing 0.50cts would typically measure 5mm in diameter. This is the most important measurement for a round brilliant cut diamond. Most ring designs come in a range of setting sizes to accommodate different sizes of a diamond. We would give a 5mm setting, suitable for this particular stone.

The other reason a diamond would be measured would involve estimating a carat weight without using scales. When setting a diamond into a ring, it is not necessarily possible to remove it to weigh the stone. The diamond measurement will give information to find the weight, referenced using size charts, providing a clear note of the carat weight. This is often necessary for determining a jewellery item’s value, especially for insurance.

The third reason is for recording specific data on a particular diamond. Producing a diamond certificate involves the laboratory noting the specific diamond measurements on the diamond grading report. If your diamond possesses a diamond certificate, you can see find this measurement among the main information near the top of the report. Look at our example dossier certificate as an example.

What diamond measurements to take

There are 3 x measurements to consider for most diamonds. The diameter or length x width measurements are usually most relevant for selecting appropriate ring mount sizes. The depth will be critical in some circumstances where a deep stone exceeds the depth of the ring setting. Formulae for calculating carat weight also need a depth measurement. (see main photo for measuring depth on the gauge.)

Round Brilliant Cut DiamondsDiameter – Diameter (this is the subtle difference from smallest to largest reading) x depth from table to culet.

Princess Cut DiamondsLength x Width (most princess cuts are not perfectly square but if the diamond is, length and width will be equal x depth from table to culet.)

Emerald Cut / Baguette Cut Diamonds  – Length x width x depth

Trilliant Cut DiamondsTypically measured point to point x depth.

Mark Johnson

About Mark Johnson

Mark attended Liverpool University and went on to pursue a career in the diamond industry. After more than a decade working in polished diamonds, Mark moved to the Isle of Wight where he launched Serendipity Diamonds. He works most days from their busy Ryde showroom, photographing jewellery and writing for the Serendipity Diamonds website. Anyone interested can connect with Mark on Linkedin via the profile link.

Mark Johnson

About Mark Johnson

Mark attended Liverpool University and went on to pursue a career in the diamond industry. After more than a decade working in polished diamonds, Mark moved to the Isle of Wight where he launched Serendipity Diamonds. He works most days from their busy Ryde showroom, photographing jewellery and writing for the Serendipity Diamonds website. Anyone interested can connect with Mark on Linkedin via the profile link.