Carat is weight, not width, so the size of a lab-grown diamond stud on your ear depends on its measured diameter.
Carat is weight; millimeters are size
One carat is 0.20 grams. What you see on your ear is the width across the top of each lab-grown diamond, and that width is measured in millimeters.
Two lab-grown diamonds with the same carat weight can differ in width. The cut decides how the weight is spread. A well-cut round lab-grown diamond of one carat measures about 6.4 to 6.5 millimeters across, while a poorly proportioned one of the same weight can measure noticeably less.
A pair's carat weight is split between two studs
Stud earrings are sold as a pair, and a pair is described by its carat total weight (ctw): both studs together. A pair of 1.00 ctw is two studs of 0.50 ct each. The size on each ear follows the weight of one stud, not the total.
This is a common reason a stud looks smaller than expected. Read the ctw as a total, halve it, then look at the millimeter size of one stud.
Round lab-grown diamond averages
Typical averages for well-cut round brilliant lab-grown diamonds, not measurements of any D2 piece. Each lab-grown diamond varies with its cut.
- 0.50 ctw pair: 0.25 ct each, about 4.0 mm across.
- 1.00 ctw pair: 0.50 ct each, about 5.1 mm across.
- 1.50 ctw pair: 0.75 ct each, about 5.8 mm across.
- 2.00 ctw pair: 1.00 ct each, about 6.4 mm across.
- 3.00 ctw pair: 1.50 ct each, about 7.3 mm across.
- 4.00 ctw pair: 2.00 ct each, about 8.1 mm across.
Fancy shapes such as oval or pear have a different outline. For any shape, trust the measurement on the product page.
Picture it on your ear
Numbers on a screen are hard to judge, so test the size in the mirror.
- Take the millimeter size of one stud from the product page.
- Use a ruler to draw a circle on paper with that diameter, and cut it out.
- Hold the circle against your earlobe in a mirror, centered where a stud would sit.
- Repeat with the next size up and the next size down, and compare the three.
What else changes how a stud looks
- Setting: the metal around the lab-grown diamond adds to the visible footprint.
- Shape: a round stud reads as a dot of light. An oval or pear reads as a longer line.
How D2 shows stud size
On a D2 stud pair, the product page lists the size of each lab-grown diamond in millimeters. The pair's total carat weight is listed beside it.
Browse the earrings and test the millimeter sizes in the mirror.
We source your lab-grown diamond.
Sources
- Federal Trade Commission, Jewelry Guides, 16 CFR 23.18 (ecfr.gov), accessed 2026-10-08