Diamond Basics
Carat Weight vs. Face-Up Size: Why They Diverge
Two diamonds of identical carat weight can look noticeably different in size depending on their cut, shape and proportions.
Why weight and diameter aren't linear
Carat is a measure of mass, not size. A diamond cut deep carries extra weight hidden below the girdle, which adds carat weight without adding to the visible face-up diameter.
Shape changes the equation
Elongated shapes such as ovals, marquises and pears spread weight over a longer outline and tend to look larger per carat than rounds, while deep cushions or princess cuts can look smaller than their weight suggests.
Using millimetre measurements
Comparing the millimetre length and width listed on a grading report is a more reliable way to judge apparent size than carat weight alone, especially when comparing different shapes.
Buyer checklist
- ✓ Compare millimetre dimensions, not just carat weight
- ✓ Check depth percentage for signs of hidden weight
- ✓ Factor in shape when estimating apparent size
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