The standard stock stud in a jewelry store is 5 mm, and it is wrong for at least half the customers who buy it. A 5 mm round on a narrow earlobe looks like a marble glued to skin; the same 5 mm on a broader earlobe reads almost invisible. Custom studs exist because the millimeter should be chosen to the ear, not to a catalog. This is the size guide we walk through with wholesale buyers before they place a semi-mount order.
The millimeter-to-carat mapping everyone wants
Studs are sold by both millimeter and carat weight, but the millimeter is the number that actually changes the look. For round brilliant diamonds, the conversions are approximate: 4 mm is 0.25 ct, 5 mm is 0.50 ct, 6 mm is 0.75 ct, 6.5 mm is 1.0 ct, 7.5 mm is 1.5 ct, and 8 mm is 2.0 ct. On colored stones, the same millimeter weighs more or less depending on density. We verify the stone measurements against the IGI grading notes when we set a custom stud, because a 5 mm sapphire and a 5 mm diamond read very different weights on the ear.
Picking the size to the ear
Narrow earlobes (under 12 mm long). 4 to 5 mm studs. Anything above 6 mm overwhelms the lobe and pulls the piercing hole forward.
Average earlobes (12 to 18 mm). 5 to 6.5 mm. This is the everyday range, and the range most of our wholesale orders land in.
Full earlobes (over 18 mm). 7 to 8 mm. Smaller studs get lost visually, and the piercing hole looks oversized next to the stone.
Face shape also matters. Long faces read better with wider studs (closer to 6.5 mm), because the horizontal width balances the vertical length. Round faces read better with slightly smaller, higher-set studs, because the earring becomes a vertical accent rather than another horizontal circle. Hair length shifts this too: hair-up moments favor a larger stud because the ear is fully visible; hair-down moments favor a smaller stud because only the lower edge shows.
What else changes the size math
Backing choice matters. A heavy push-back on a 6.5 mm stone pulls the stud down through the piercing, which makes the stone sit low. We use ear nuts (screw backs) on studs over 6 mm to keep the stone sitting flush. For clients who want studs they can wear to sleep, we recommend 4 to 5 mm with flat backs, because posts poking into the scalp are the number-one complaint we hear about larger studs. Build out the stud-to-drop wardrobe in studs to drops, explore the climber alternative in studs to climbers, and see how colored stones change the proportion in custom gemstone earrings. For a statement option, long drops covers the other end of the size spectrum.
Wholesale buyers: we stock calibrated stud semi-mounts in 4, 5, 6 and 6.5 mm rounds in 14k yellow, rose and white gold. MOQ is 20 pairs per size. Custom head shapes (pear, oval, cushion) are quoted on request.
Two bench details wholesale buyers should know. First, the post gauge. We use 0.8 mm posts on 4 to 5 mm studs and 1.0 mm posts on 6.5 mm and up. A post too thin on a heavy stone bends over time; a post too thick on a small earlobe stretches the piercing. Second, the stone setting style. Bezel-set studs read smaller than prong-set studs of the same millimeter, because the bezel covers 0.3 mm of the stone edge. If the customer wants the stone to read as large as possible, quote prong. If she wants a clean, protective look, quote bezel.
Wholesale stock note: we move more 5 mm studs than every other size combined, roughly 60 percent of stud orders. The 6 mm size is the second mover at 20 percent. The 4 mm and 6.5 mm sizes split the remaining 20 percent. If you are placing a first semi-mount order, weight the buy 60/20/10/10 across 5, 6, 4 and 6.5 mm. That covers the everyday customer without leaving slow-moving stock on the shelf. Custom 8 mm studs are almost always made to order rather than stocked, because the carat weight pushes the price into a bridal bracket.
What size stud is considered everyday?
5 mm (roughly 0.50 ct total) is the default everyday stud. It is visible at a meeting but not loud on a video call.
Can I mix sizes on the two ears?
Not on a single piercing. The eye expects a pair to mirror. Mixed sizes work only when the two ears carry different piercings (one stud, one huggie).
Do studs come in half sizes?
Round brilliant stones are calibrated in 0.5 mm steps. We can set a 5.5 mm stone if the customer's earlobe falls between the 5 and 6 stock sizes.
What backing is best for sensitive ears?
Solid 14k screw backs. Nickel-containing alloy backs are the most common source of stud-ear irritation, even when the post itself is gold.
How much bigger should studs be for a second hole?
Smaller. A second-hole stud at 3 to 4 mm reads as a high note, not a second main. Same-metal pairs always look cleaner than mixing metals across two holes.
