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Diamond Education Guide from Diamond Heaven Diamond Education Guide from Diamond Heaven


Carat refers to the weight of a diamond. Diamonds are all weighed in metric carats rather than grams or ounces. This is a standard industry practice around the world.

Diamond is expressed to the hundredth of a carat. Carat weight of less than a carat is expressed in points. So, for example, a 0.75ct diamond will be 75 points. Most jewellers will refer to carat weight in this terminology.

Another way to explain this would be using pounds, 100 pence equals 1 whole pound. Therefore 50pts will be 0.50ct and so on.


A common misconception is that it refers to the physical size of a diamond, which is incorrect. The diamond weight does not govern the size of stone.

We always recommend trying a range of carat weight on to determine which will be best for you. This way you will also be able to assess the visible size. For those who can’t come into our store to view diamonds we have the chart below to give you an indication on size.

  Carat Weight 0.25ct 0.50ct 0.75ct 1ct 1.50ct 2ct 3ct 4ct 5ct Carat Weight
Round round 4mm 5mm 5.50mm 6.50mm 7.50mm 8mm 9.40mm 10.40mm 11.20mm round
Princess Princess 3.50mm 4.50mm 5mm 5.50mm 6.80mm 7.50mm 8mm 8.90mm 9.70mm Princess
Heart Heart 4x4mm 5x5mm 6x6mm 6.50x6.50mm 7x7mm 8x8mm 9x9mm 10x10mm 11x11mm Heart
Emerald Emerald 4x3mm 6x4mm 6.50x4.50mm 7x5mm 8x6mm 8.50x6.50mm 10x8mm 11x9mm 10x10mm Emerald
Asscher Asscher 3.70mm 4.40mm 5mm 5.80mm 6.40mm 7mm 8.10mm 9mm 9.60mm Asscher
Marquise Marquise 5x3mm 8x4mm 9x4.50mm 10x4.75mm 11x5mm 12x6mm 14x7mm 15x7mm 16x8mm Marquise
Radiant Radiant 3.50x3mm 5x4.50mm 5.50x5mm 6x5.50mm 7x6mm 7.50x7mm 8.50x7.50mm 9.50x8.50mm 10x9mm Radiant
Cushion Cushion 4x3.50mm 5x4.50mm 6x5mm 6.50x5.50mm 7.50x6.50mm 8x7mm 9x8mm 10x8.50mm 10x9.50mm Cushion
Oval Oval 5x3mm 6x4mm 7x5mm 7.50x5.50mm 8.50x6.50mm 9x7mm 10x8mm 11x9mm 12x10mm Oval
Pear Pear 4x2mm 6x4mm 7x5mm 8x5mm 9x6mm 10x7mm 12x8mm 14x9mm 15x10mm Pear


The characteristic that makes the most difference in the visual appearance of a diamond is the cut. You will often have two diamonds of the same carat weight that are different in visual size depending on their cut.

For example, a diamond that is graded as a poor cut would have a small visual appearance, where as a very good or excellent cut would be a lot closer to the visual look you should expect. If a diamond is deeper, then it will have a smaller diameter and if it is shallow then it will have a bigger spread.


For example, you can get a 1.00ct Round diamond graded as ‘fair’ or ‘poor’ cut that measures 5.9mm. You can then have a round diamond graded as an excellent cut which measures 6.6mm approximately.

You can visit our ‘cut’ education section to get more in depth information on this. If you’re still unsure as to which carat size is for you contact us on [email protected] or 0345 222 5009.

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