How Big Is a 1, 2, 3, 4, or 5 Carat Diamond? Actual Sizes in Millimeters

Carat measures weight, not size — and what your eye sees is the face-up spread in millimeters. These are the real measurements of the round brilliant stones we set in our NYC studio:

Note: doubling the carat weight does not double the diameter — weight grows with volume. That's why a 2-carat stone looks noticeably, but not twice, bigger than a 1-carat.

Shape changes everything

Elongated shapes spread their weight across more of the finger, so they face up larger than a round of the same carat:

• Oval — the size-per-carat champion. A 3-carat oval reads visibly larger than a 3-carat round.
• Marquise — maximum length; the most finger coverage per carat of any shape.
• Emerald — elegant length, though its deep step cut holds some weight below.
• Round — the brilliance benchmark; the standard the chart above describes.
• Cushion and princess — square outlines that carry weight in depth, so they face up slightly smaller per carat but sparkle intensely.

For stud earrings, think per-ear

Studs are sold by total carat weight across the pair. A 2.00 ct total pair means a 1.00 ct diamond (~6.5 mm) on each ear — the classic "noticeable but everyday" size. A 6.00 ct total pair puts a ~9.3 mm stone on each ear — unmistakable. See every size side by side in our lab-grown diamond studs collection, from 1 to 10 total carats.

The lab-grown advantage: buy the size you actually want

Because lab-grown diamonds cost a fraction of mined stones at the same grade, the 3-carat look most people assume is out of reach usually isn't. Browse IGI-certified pieces under $2,000 or our full engagement ring collection — every stone is graded and laser-inscribed by IGI, so the size AND the quality are documented in black and white.