What a carat actually measures
A carat is a unit of weight: one carat equals 200 milligrams. It does not tell you the diamond’s width, height or beauty. Two diamonds can weigh the same and still look different in size.
The useful lesson from the original Engagement Ring Guru guide still holds: twice the carat weight does not look twice as wide. A diamond has depth as well as width, so some of that extra weight sits below the part you see.
Why equal weights can look different
A deeper diamond can hide more of its weight below the top, making it look smaller than another diamond of the same carat. But wider is not always better: cut and durability still matter.
different spread
A small change in width can be noticeable
Width is measured straight across a round diamond. Because the whole top surface grows as the diamond gets wider, even a modest increase can look meaningful. That still tells you nothing about sparkle.
The ring and the hand change the look
A wide band, halo, bezel, side stones and finger size can all make the centre diamond feel larger or smaller. Use the on-screen tool to narrow down a comfortable range, then look at real rings where you can.
What to note when comparing diamonds
- carat weight;
- the two width measurements;
- whether one diamond is unusually deep;
- the setting and band width;
- how it looks at normal viewing distance as well as zoomed in.
Sources and limits
The carat definition and the difference between weight and size are supported by the Gemological Institute of America’s carat guide. Our size tool is for visual guidance only; it does not judge sparkle, quality or value.