What Is Diamond Carat Weight? A Complete Buyer's Guide

Published: 2026-03-31 | Author: Benny Gabay

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Carat Weight vs Physical Size

Carat is a unit of weight, not size. One carat equals 0.2 grams. Two diamonds with the same carat weight can look quite different in size depending on their shape and how they were cut. A well-cut 1ct round brilliant measures approximately 6.5mm in diameter. A poorly cut 1ct stone might appear noticeably smaller due to weight being retained in the bottom of the stone (the pavilion).

How Carat Affects Price

Diamond prices increase non-linearly with carat weight because larger diamonds are significantly rarer. A rough guide to how price scales:

• A 2ct diamond does not cost twice as much as a 1ct - it typically costs 3-4 times as much
• A 3ct diamond may cost 6-8 times the price of an equivalent 1ct stone

There are also price jumps at "magic sizes" - 0.50ct, 0.75ct, 1.00ct, 1.50ct, 2.00ct. A 0.98ct diamond often costs meaningfully less than a 1.00ct stone of equivalent quality, with virtually no visible size difference.

Carat and Shape: Apparent Size Differences

Different shapes yield different apparent sizes for the same carat weight. Here's how popular shapes compare at 1 carat:

• Round Brilliant: ~6.5mm diameter
• Oval: ~7.5 x 5.5mm - appears larger than round
• Pear: ~8.5 x 5.5mm - appears larger than round
• Cushion: ~5.8 x 5.8mm - similar to round
• Emerald: ~7.0 x 5.0mm - elongated, elegant appearance
• Princess: ~5.5 x 5.5mm - compact, brilliant

If maximising apparent size is a priority, oval, pear, and marquise shapes give you more visual diamond per carat than a round brilliant.

Lab-Grown Diamonds: More Carats Per Rand

One of the most compelling advantages of lab-grown diamonds is the ability to purchase a substantially larger carat weight for the same budget. A budget that buys a 1ct natural diamond might buy a 1.5ct or even 2ct lab-grown diamond of equivalent quality. Both carry GIA or IGI certification. Both are real diamonds.

What Carat Weight Should You Buy?

There is no universal answer - it depends on budget, finger size, setting style, and personal preference. Our guidance:

• For an engagement ring solitaire, 0.7ct to 1.5ct is the most popular range in South Africa
• "Just under" sizes (0.90ct, 1.45ct) offer significant savings with negligible visual difference
• Finger size matters - a 0.7ct stone looks proportionally large on a size 5 finger and modest on a size 8 finger

Use our diamond search filters to browse by carat range across our natural and lab-grown diamond collections. Our Diamond Buying Guide has more advice on balancing carat with the other 4Cs.

For a full breakdown of current diamond prices in South Africa, see our Diamond Price Guide.