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What do you know about
diamonds
Explore the captivating world of diamonds. Learn about their origin, beauty, and the 4 Cs that define their quality. Welcome to the world of timeless elegance and enduring brilliance.
By Fiona, founder of Ronora Diamond. Updated September 26, 2026.
A 1 carat round diamond stud measures about 6.5 mm across, and a pair of them is 2 carats total weight (2 ctw). If you shop by millimeters, a 3 mm round stud weighs about 0.10 carat, a 4 mm stud about 0.23 carat and a 5 mm stud about 0.46 carat per earring, or 0.20, 0.47 and 0.91 ctw for the pair. A half carat stud is 5.2 mm across and a quarter carat stud 4.1 mm. Shape changes the look at the same weight: a 1 carat princess stud is 5.5 mm square and a 1 carat oval 7.7 × 5.7 mm. Use the calculator on this page to see any stud on an ear lobe at actual size.
Choose Earrings, pick a shape and set the carat weight of one earring. The stud is drawn on an ear lobe at true scale in a three prong setting, set vertically or horizontally. Already know the diameter you want? Switch to millimeters and the calculator gives the carat weight. Calibrate once against a bank card so the drawing matches real life on your screen.
Measure the longest axis and the widest axis of the face-up outline. Carat weight is estimated from those two figures and the proportions this shape is normally cut to.
A 1.00 ct round measures
6.50 × 6.50 mm
Drawn at true physical size once your screen is calibrated. Hold a ring up to the outline to judge it properly.
Hold any bank card against the bar below and drag the slider until the two match exactly. A standard card is 85.6 mm wide. Your setting is remembered on this device.
Same weight, twelve outlines. The bars are drawn to scale against each other, longest first.
Millimeter figures are for well proportioned stones cut to the ratio shown. Individual stones vary, so ask us for the exact measurements on any stone before you order. The Dutch Marquise is one of our own cuts and has no published trade chart; those figures are Ronora's working sizes.
Carat weight per earring and for the pair, with the face-up size of each stud in millimeters. Round and heart studs share the same size at each weight in our proportions; princess and cushion are more compact because more of their weight sits below the surface.
| Each earring | Pair total (ctw) | Round (mm) | Princess (mm) | Cushion (mm) | Heart (mm) |
|---|---|---|---|---|---|
| 0.25 ct | 0.50 ct | 4.1 × 4.1 | 3.5 × 3.5 | 3.5 × 3.5 | 4.1 × 4.1 |
| 0.33 ct | 0.66 ct | 4.5 × 4.5 | 3.8 × 3.8 | 3.8 × 3.8 | 4.5 × 4.5 |
| 0.50 ct | 1.00 ct | 5.2 × 5.2 | 4.4 × 4.4 | 4.4 × 4.4 | 5.2 × 5.2 |
| 0.75 ct | 1.50 ct | 5.9 × 5.9 | 5.0 × 5.0 | 5.0 × 5.0 | 5.9 × 5.9 |
| 1.00 ct | 2.00 ct | 6.5 × 6.5 | 5.5 × 5.5 | 5.5 × 5.5 | 6.5 × 6.5 |
| 1.25 ct | 2.50 ct | 7.0 × 7.0 | 5.9 × 5.9 | 5.9 × 5.9 | 7.0 × 7.0 |
| 1.50 ct | 3.00 ct | 7.4 × 7.4 | 6.3 × 6.3 | 6.3 × 6.3 | 7.4 × 7.4 |
| 2.00 ct | 4.00 ct | 8.2 × 8.2 | 6.9 × 6.9 | 6.9 × 6.9 | 8.2 × 8.2 |
| 2.50 ct | 5.00 ct | 8.8 × 8.8 | 7.5 × 7.5 | 7.5 × 7.5 | 8.8 × 8.8 |
| 3.00 ct | 6.00 ct | 9.4 × 9.4 | 7.9 × 7.9 | 7.9 × 7.9 | 9.4 × 9.4 |
The pair total is simply twice the weight of one earring. Choose Earrings in the calculator on this page, or open a 1 carat round stud in Find Me Diamond.
Elongated studs, length by width in millimeters. Set vertically, the first number runs down the lobe.
| Each earring | Pair total (ctw) | Oval (mm) | Emerald (mm) | Pear (mm) | Radiant (mm) |
|---|---|---|---|---|---|
| 0.25 ct | 0.50 ct | 4.8 × 3.6 | 4.4 × 3.1 | 5.0 × 3.3 | 3.9 × 3.0 |
| 0.33 ct | 0.66 ct | 5.3 × 3.9 | 4.8 × 3.5 | 5.5 × 3.7 | 4.3 × 3.3 |
| 0.50 ct | 1.00 ct | 6.1 × 4.5 | 5.6 × 4.0 | 6.3 × 4.2 | 5.0 × 3.8 |
| 0.75 ct | 1.50 ct | 7.0 × 5.2 | 6.4 × 4.5 | 7.2 × 4.8 | 5.7 × 4.4 |
| 1.00 ct | 2.00 ct | 7.7 × 5.7 | 7.0 × 5.0 | 7.9 × 5.3 | 6.2 × 4.8 |
| 1.25 ct | 2.50 ct | 8.3 × 6.1 | 7.5 × 5.4 | 8.6 × 5.7 | 6.7 × 5.2 |
| 1.50 ct | 3.00 ct | 8.8 × 6.5 | 8.0 × 5.7 | 9.1 × 6.1 | 7.1 × 5.5 |
| 2.00 ct | 4.00 ct | 9.7 × 7.2 | 8.8 × 6.3 | 10.0 × 6.7 | 7.9 × 6.0 |
| 2.50 ct | 5.00 ct | 10.4 × 7.7 | 9.5 × 6.8 | 10.8 × 7.2 | 8.5 × 6.5 |
| 3.00 ct | 6.00 ct | 11.1 × 8.2 | 10.1 × 7.2 | 11.5 × 7.6 | 9.0 × 6.9 |
Elongated studs measure longer than a round of the same weight but narrower. Try the vertical and horizontal settings in the calculator to see which suits your ear.
If you know the diameter you want, read across to the carat weight. A well cut round diamond of 6.5 mm weighs about 1 carat, and the last two columns show the size of a princess or an oval of exactly the same weight.
| Round stud diameter | Carat each | Pair total (ctw) | Princess of the same weight (mm) | Oval of the same weight (mm) |
|---|---|---|---|---|
| 3.0 mm | 0.10 ct | 0.20 ct | 2.5 × 2.5 | 3.6 × 2.6 |
| 3.5 mm | 0.16 ct | 0.31 ct | 3.0 × 3.0 | 4.1 × 3.1 |
| 4.0 mm | 0.23 ct | 0.47 ct | 3.4 × 3.4 | 4.7 × 3.5 |
| 4.5 mm | 0.33 ct | 0.66 ct | 3.8 × 3.8 | 5.3 × 3.9 |
| 5.0 mm | 0.46 ct | 0.91 ct | 4.2 × 4.2 | 5.9 × 4.4 |
| 5.5 mm | 0.61 ct | 1.21 ct | 4.7 × 4.7 | 6.5 × 4.8 |
| 6.0 mm | 0.79 ct | 1.57 ct | 5.1 × 5.1 | 7.1 × 5.3 |
| 6.5 mm | 1.00 ct | 2.00 ct | 5.5 × 5.5 | 7.7 × 5.7 |
| 7.0 mm | 1.25 ct | 2.50 ct | 5.9 × 5.9 | 8.3 × 6.1 |
| 7.5 mm | 1.54 ct | 3.07 ct | 6.3 × 6.3 | 8.9 × 6.6 |
| 8.0 mm | 1.86 ct | 3.73 ct | 6.8 × 6.8 | 9.5 × 7.0 |
Weights are rounded to two decimals, so a pair total can differ from twice the single figure by 0.01. Diameter grows slowly with weight: a 5 mm stud weighs 0.46 carat and an 8 mm stud 1.86 carat, about 4 times as much, for a diameter only 3 mm larger.
Lab grown diamond studs in D-E-F colorless with VVS-VS clarity, made in 9K, 14K or 18K solid gold, platinum or 925 silver. Our sizes are pair totals, so for 1 carat in each ear choose 2 ct TCW.
Choose by millimeters first and let the carat weight follow. Carat is a weight, so it tells you how much diamond you are paying for, while the diameter tells you what people actually see on the ear.
As a guide to the look: round studs of 3 to 4 mm (0.10 to 0.23 carat each) are quiet and neat, and they suit a second or third piercing. Studs of 4.5 to 5.5 mm (0.33 to 0.61 carat each) are the classic everyday size, clearly visible in conversation. From 6 mm upward (0.79 carat each and more) the stud becomes a focal point of the face, and at 6.5 mm a 1 carat stud is a confident, clearly visible pair.
Think about how you wear your hair, how often you will wear the pair, and whether it sits next to other earrings. If you are between two sizes, compare them in the calculator on this page, for example a 0.5 carat round stud against a 1 carat round stud. Half a millimeter is much easier to judge at actual size than in words.
Stud earrings are described in two ways, and it is easy to mix them up. Carat total weight, written ctw or ct tw, is the combined weight of both earrings. Carat per earring is the weight of one stone.
So a pair sold as 1 ctw holds two 0.5 carat diamonds, each about 5.2 mm across in a round. A pair sold as 2 ctw holds two 1 carat diamonds of about 6.5 mm each. Going from 1 ctw to 2 ctw doubles the weight but adds only about 26% to the diameter of each stud, because diameter grows with the cube root of weight.
When you compare prices from different jewelers, always convert to the same basis first. The charts on this page show the weight of each earring and the pair total side by side, so you can see exactly what you are comparing and what will arrive in the box.
The ear lobe is a small canvas, so a fraction of a millimeter shows more there than it does on a hand. A 0.25 carat round stud at 4.1 mm and a 0.5 carat stud at 5.2 mm differ by only 1.1 mm, yet side by side the larger one looks noticeably fuller, because the lobe around it stays the same size.
Distance matters too. Studs are seen at conversation distance and often from the side, where the setting and the metal around the stone add to the visible size. A four prong basket or a bezel frames the stone and can make it read a touch larger, while a three prong martini setting sits closer to the lobe.
Your piercing position changes the look as well, so judge a size on your own ear. After calibrating the calculator, hold your phone next to your ear in a mirror and you will see the stud at its real size against your own lobe.
At the same weight, elongated shapes measure longest and square shapes measure smallest. At 0.5 carat per earring, a round stud is 5.2 mm across, an oval 6.1 × 4.5 mm, a pear 6.3 × 4.2 mm and an emerald cut 5.6 × 4.0 mm. A princess or cushion of the same weight is 4.4 mm square, and a heart 5.2 × 5.2 mm.
The princess is smaller by the ruler, but its square corners fill the whole outline, so on the ear it holds its own against a round. Elongated shapes can be set vertically, which draws the eye down the lobe, or horizontally, which reads wider and more modern. The calculator has a vertical and horizontal switch for exactly this choice: try an oval stud set vertically.
Round studs are the classic choice and look the same from every angle. Emerald cuts show long, mirror-like flashes rather than sparkle, and hearts read most clearly as hearts once the stone is large enough for the cleft to show. Read more in the diamond shapes guide.
Every figure on this page is a face-up measurement, length by width in millimeters, for a well proportioned stone cut to the classic ratio for its shape. It is the size you see when you look straight at the ear, not the depth of the stone behind it.
Individual diamonds vary by a few tenths of a millimeter depending on how deep they are cut, which is why two studs of the same weight can measure slightly differently. Every Ronora pair is made to order in Surat, so you can ask us for the exact measurements of both stones before you order.
Every Ronora diamond is a real CVD lab grown diamond, Excellent cut, D-E-F colorless with VVS clarity. Browse lab grown diamond earrings, or send us the size you want in millimeters and we will tell you the carat weight that gives it. For the science behind the numbers, see our carat weight guide.
Between 0.25 and 0.5 carat per earring, 4.1 to 5.2 mm across in a round, is an easy everyday size: visible in conversation without dominating the lobe. For studs that read clearly from further away, 0.75 to 1 carat each, 5.9 to 6.5 mm, is the next step. Compare two sizes on the ear in the calculator before you decide.
A 1 carat round stud is about 6.5 mm across, a little over a quarter of an inch, and a 1 carat princess stud about 5.5 mm square. Note that "1 carat diamond earrings" often means 1 carat total for the pair, which is two 0.5 carat studs of about 5.2 mm each. Check which one a listing means before you compare prices.
A 2 ctw pair is two 1 carat diamonds of about 6.5 mm each, a confident size that is still a stud rather than a statement drop. They work every day if you like a visible stud. On small lobes, a 1.5 ctw pair at 5.9 mm each gives a similar look with less of the lobe covered, so compare both at actual size.
A classic everyday diamond stud is about 3 to 5 mm across, which in a round is roughly 0.10 to 0.46 carat per earring. Studs of 5.5 to 6.5 mm (0.61 to 1.00 carat each) make a larger, more noticeable pair. There is no single normal size, so choose by how visible you want the stones to be.
A 3 mm round diamond stud weighs about 0.10 carat, a 4 mm stud about 0.23 carat and a 5 mm stud about 0.46 carat. For the pair, double it: about 0.20, 0.47 and 0.91 ctw. These figures are for well cut round diamonds; other shapes of the same weight measure differently, as the charts on this page show.
A 0.5 carat round stud is about 5.2 mm across, and a 0.5 carat oval about 6.1 × 4.5 mm. Be careful with the wording: "half carat diamond earrings" often means 0.5 carat total for the pair, which is two 0.25 carat studs of about 4.1 mm each. Both are easy everyday sizes.
A 1 carat round stud is 6.5 mm across, a little over a quarter of an inch, which reads as a confident everyday stud rather than a cocktail piece. If your lobes are small or you prefer a quieter look, a 0.75 carat stud at 5.9 mm or a 1 carat princess at 5.5 mm square covers less of the lobe. See both on the ear before you decide.
CTW means carat total weight, so a 1 ctw pair is two 0.5 carat studs of about 5.2 mm each. A pair described as 1 carat each is 2 ctw, with studs of about 6.5 mm. Always check whether a price is for the weight of each earring or for the pair, because the two can look almost identical in a listing.
At 0.5 carat per earring, a pear measures longest at 6.3 × 4.2 mm, followed by an oval at 6.1 × 4.5 mm, against 5.2 mm for a round. Square shapes measure smaller: a 0.5 carat princess or cushion is 4.4 mm square. Set vertically, elongated studs draw the eye down the lobe; set horizontally they read wider.
Measure the widest point of the stone face-up in millimeters, not the setting: a round stud that measures 5 mm weighs about 0.46 carat. A caliper is the most accurate tool, and a millimeter ruler held against the stone works as a check. Then read across the millimeter chart on this page, or enter the size in the calculator in millimeter mode.
