Before grams and ounces, diamonds were weighed using carobs, a long green bean with seeds inside. The beans were nearly identical in size, making them ideal for Mediterranean traders to use when weighing gemstones. One seed equalled one carob, which is likely where the term carat originates.
Carat is often confused with the size of a diamond even though it’s actually a unit that measures its weight. Today, one carat is equal to 0.2 grams.
It can be hard to get a sense of how big a diamond is going to be without having it there in front of you. To help you get a better sense of what size diamonds of different carat weight are in real life, we’ve made this diamond size chart.
This is what a round brilliant diamond looks like next to a standard sized pencil, ranging from 0.60ct to 3ct. We’ve also included a diamond size conversion from carat to mm (carats to millimetres).
Want to see what different carat weights, diamond shapes, and band widths look like on your hand? Download and print this PDF and you’ll be able to cut out to-scale outlines of virtually every diamond size and shape. You can mix and match them on different ring band sizes to get a better idea of what your ring will look like in real life.
Because larger diamonds are more rare, the heavier the diamond, the higher the price.
Though price increases aren’t steady—they can increase exponentially with carat weight. For example, a 1 carat diamond would be valued higher than two 0.50 carat diamonds of the same quality.
In general, a doubling the size of your diamond can cost three to four times more.
Highly sought-after diamond sizes can also carry a price premium. If you’re after a 1, 1.5 or 2 carat etc. we recommend buying just shy of these carat weights, which can result in savings.
Just because a diamond is bigger, doesn’t mean it’s better.
The right diamond isn’t just based on one factor but a combination of all 4 Cs (carat, cut, clarity and colour). When choosing a diamond, focus on the quality that’s most important to you, then work to balance the remaining three.
While carat weight is a measure of a diamond’s weight, and not its size, it is a consistent indicator of how large a diamond will look, when viewed from the top. Play around with our carat weight widget below to see how different carat weights look in different shapes and styles.
If you’re keen to stick within a set price point, it’s worth noting that diamonds of the same carat weight, but of a different shape will be priced differently.
For example, round diamonds carry a premium over other shapes because they produce the most waste in their cutting process.
Choosing a fancy shape will often provide you with better value than choosing a much sought-after round diamond.
The chart below shows the prices of a one carat G colour grade, VS2 clarity grade diamond in various shapes. These prices will increase on average should you increase the quality grades of the diamond and decrease on average should you decrease the quality grades of the diamond.
| Shape | Carat Weight | Price |
| Round | 1.00 | £5,796 |
| Oval | 1.00 | £4,773 |
| Princess | 1.00 | £4,272 |
| Marquise | 1.00 | £5,206 |
| Cushion | 1.00 | £3,382 |
| Emerald | 1.00 | £3,568 |
| Pear | 1.00 | £4,783 |
Amongst our customers, we see an average carat weight of around 0.79ct.
Coloured gemstones often provide slightly better value for money, resulting in an average carat weight for coloured gemstones averaging at around 0.96ct.