The size of a diamond is an integral part of both its worth and visual appeal. But diamonds are generally measured in weight, rather than millimetres, so understanding how this measurement relates to what you see isn’t always obvious.
So let’s dive into diamond size, and examine how we decipher carats, points, and millimetres - and why it matters.
Understanding carat weight
A diamond’s size is typically communicated by weight, using a measurement called carats. We would never use grams to describe a diamond, but one carat is equivalent to 200 milligrams, or 0.2 grams. A stone described as a ‘one- carat diamond ’ will weigh exactly 200 milligrams.
Carat weight doesn’t always translate directly into the visual size of the diamond, however. Two diamonds of equal carat weight might look very different from one another, depending on their shape and cut.
If we look at ideal cut parameters, a 1.00ct diamond should measure about 6.5mm. But a stone that is cut deeper will look smaller from the top, and one that is shallower will have a larger spread. The girdle thickness and proportions can affect the perceived carat size and brilliance of the diamond, as irregular proportions may not reflect light optimally.
You may sometimes hear diamonds described in ‘points’. Diamonds less than one carat are sometimes measured this way, with one carat equal to 100 points. A diamond that weighs half a carat - or 0.50cts - could also be described as a 50-point diamond.
How to determine the size of a diamond
Carat weight is a key factor affecting price. Larger diamonds are rarer and, therefore, more valuable.
However if you’re choosing a diamond for your engagement ring, you may be more concerned with how it looks than how much of an investment it might be. We call how large a diamond looks its ‘spread’. Understanding diamond measurements, including shape and cut proportions, is crucial for assessing a diamond's beauty and value.
Measuring the spread of a diamond is a case of taking the diameter in millimetres across the top of the stone. A symmetrical diamond such as round will have one measurement - eg. 6.5mm - while a stone such as emerald, pear or marquise will have two measurements - eg. a 7x5mm emerald. A diamond size chart can be a useful resource for estimating the physical dimensions of diamonds in relation to their carat weight.
Due to their individual cuts, different shaped diamonds will have different carat weights. For instance, a 1.00ct round diamond is about 6.5mm, but a 1.00ct princess cut stone will measure around 5.5mm.
Using an app to measure diamond size
There’s an app for everything, so you might wonder if there’s an app to measure diamond size. And yes - there are actually several smartphone apps available that can estimate the size of your diamond. Generally, diamond sizing apps use the phone’s camera to approximate the dimensions of your diamond.
Although they can be fun and reasonably useful, these apps can only ever provide an estimate of a diamond's size, which refers to how large it appears from above. Do not rely on an app for measuring a diamond you are purchasing or selling - or to assess how generous a present may have been! For a more accurate idea of size, speak with a professional jeweller or gemologist.
Balancing size and sparkle
The size and weight of a diamond are just two factors affecting a diamond’s beauty and value. As we’ve explored, the size of a diamond is determined by its cut - and in turn, the cut of a diamond influences its brilliance.
The cut determines how light reflects and refracts within the diamond, which is what creates its distinctive brilliance and contributes to the diamond's brilliance. An ideal cut diamond of any shape or size is cut to the perfect proportions for maximum sparkle.
A diamond that is significantly outside the ideal, or standard, cut parameters may be cheaper than a diamond with perfect proportions.
Selecting the perfect diamond involves considering factors beyond just carat weight, such as shape, cut, and proportions.
On one hand, this may be a good way to get your target carat weight for a slightly lower cost. But on the other hand, it may be better value to go for a lower carat weight with a better cut. Cut influences the sparkle and fire of a diamond, and a stone that is too shallow or deep may sacrifice some of the life. The length to width ratio also influences the visual appeal of diamonds, with ideal ratios varying for different cuts.
Diamond size can be measured in both carat weight and mm size. When choosing fine jewellery, perhaps more important than a measurement is how those sizes relate to brilliance and beauty.
How we can help!
We can help guide you through the complexities of diamond size, helping you balance budget with brilliance, and size with sparkle!
We're here to help. Reach out to us on info@harpertait.com and we’ll help you navigate the process with ease! Or find your perfect diamond wedding ring or diamond engagement ring in our collection
