Diamond Size Chart: What a Carat Actually Measures in Millimetres

There is a moment that happens often enough in Indian jewellery buying to be almost predictable. Someone orders a one carat solitaire online, waits for it, opens the box, and finds a stone that is unmistakably smaller than the one in their head. Nothing was misdescribed. The listing said one carat. The stone weighs one carat. And it still looks wrong.

This happens because almost every diamond size chart circulating online answers a question slightly different from the one being asked. The buyer wants to know how big the stone will look. The chart tells them how much it weighs. Those two things are related, but the relationship depends on what the stone is made of, and most charts never mention that.

This guide is built around the number that survives every conversion: the millimetre. Carats change meaning depending on material. Millimetres do not.

Carat measures weight, not width

One carat is 200 milligrams. That is the entire definition. It says nothing about diameter, spread, or how much of a finger a stone covers.

The gap between weight and appearance is not a technicality. It is the single largest source of disappointment in online stone buying, because weight is buried inside the stone where nobody can see it. A deeply cut stone hides carat weight in its pavilion, below the girdle, where it contributes to the price and nothing else. A shallower stone of identical weight spreads wider and reads larger. Same number on the invoice, different stone on the hand.

If you take one thing from this page, take this: ask for the millimetre measurement. It is the only figure that describes what you will actually see.

For the separate and frequently confused question of gold purity, karat and carat are unrelated units, which KYMEE covers in karat vs carat.

The round brilliant chart, with cents

Round brilliant is the reference shape for every size chart because it is symmetrical and its proportions are the most standardised.

Here is the conversion, with the column Indian jewellers actually speak in.

Diameter (mm)	Carat weight	Spoken as (India)
2.0 mm	0.03 ct	3 cents
2.5 mm	0.06 ct	6 cents
3.0 mm	0.10 ct	10 cents
3.5 mm	0.15 ct	15 cents
4.0 mm	0.25 ct	25 cents
4.5 mm	0.35 ct	35 cents
5.0 mm	0.50 ct	50 cents, half carat
5.5 mm	0.65 ct	65 cents
6.0 mm	0.80 ct	80 cents
6.5 mm	1.00 ct	1 carat
7.0 mm	1.25 ct	1.25 carat
7.5 mm	1.50 ct	1.5 carat
8.0 mm	2.00 ct	2 carat
8.5 mm	2.40 ct	2.4 carat
9.0 mm	2.75 ct	2.75 carat

That third column matters more than it looks. Walk into a jeweller in Surat, Coimbatore or Jaipur and ask about a stone, and the answer often comes back as "thirty cents" or "a fifty pointer." One carat divides into 100 cents, exactly as one rupee divides into 100 paise. A 0.30 ct stone is a thirty cent stone. International size charts almost never carry this column, which is why they feel one step removed from an actual counter conversation in India.

Notice also how the numbers behave. Going from 6.5mm to 8.0mm doubles the weight from one carat to two. The diameter grows by only 1.5mm, and the face-up area you actually see grows by about 51%. Weight doubles, visible size grows by half. This is why jumping a full carat rarely looks like twice the stone, and why the price jump feels disproportionate to the visual return.

Shape changes the footprint more than weight does

At a fixed one carat, here is roughly what different shapes measure.

Shape	Approximate dimensions at 1 carat
Round brilliant	6.5 mm diameter
Princess	5.5 x 5.5 mm
Cushion	5.5 x 5.5 mm
Asscher	5.5 x 5.5 mm
Radiant	6.2 x 5.2 mm
Emerald	7.0 x 5.0 mm
Oval	7.70 x 5.70 mm (Typical)/8.00 x 5.50 mm (Elongated)
Pear	7.7 x 5.7 mm
Marquise	10.0 x 5.0 mm

A one carat marquise runs ten millimetres long. A one carat princess runs five and a half. Identical weight, and the marquise covers noticeably more finger. Elongated shapes carry less of their weight in depth, so more of it appears at the surface.

This is the cheapest lever available to anyone who wants presence without paying for it. Oval, pear and marquise read larger per carat than round, princess or cushion. If the goal is a stone that looks substantial on a slim finger, shape does more work than weight. KYMEE's solitaire rings run across round, oval, pear, marquise, emerald and cushion for exactly this reason, and the elongated cuts consistently look larger than their weight suggests.

Elongation has a trade-off worth knowing. Marquise and pear shapes have points, and points are the most vulnerable part of any set stone. For daily wear, particularly in India where jewellery tends to stay on through cooking, commuting and housework, a bezel setting that encloses the point is meaningfully more durable than exposed prongs. KYMEE's dainty rings and daily wear rings lean on bezel and low-profile settings for this reason.

Marquise Size Chart

Carat Weight	Standard MM Dimensions (Length × Width)
0.25 ct	6.0 × 3.0 mm
0.50 ct	8.0 × 4.0 mm
0.75 ct	9.0 × 4.5 mm
1.00 ct	10.0 × 5.0 mm
1.25 ct	10.5 × 5.25 mm
1.50 ct	11.5 × 5.5 mm
2.00 ct	12.5 × 6.25 mm
3.00 ct	14.5 × 7.25 mm

Baguette Size Chart

Carat Weight	Standard MM Dimensions (Length × Width)
0.10 ct	3.5 × 1.8 mm
0.25 ct	4.5 × 2.2 mm
0.50 ct	6.0 × 3.0 mm
0.75 ct	6.5 × 3.5 mm
1.00 ct	7.0 × 4.0 mm
1.50 ct	8.0 × 5.0 mm
2.00 ct	9.0 × 6.0 mm

Oval Size Chart

Carat Weight	Standard MM Dimensions (Length × Width)
0.25 ct	5.0 × 3.5 mm
0.50 ct	6.3 × 4.4 mm
0.75 ct	7.0 × 5.0 mm
1.00 ct	7.7 × 5.7 mm (Typical) / 8.0 × 5.5 mm (Elongated)
1.25 ct	8.5 × 6.0 mm
1.50 ct	8.8 × 6.2 mm
2.00 ct	9.2 × 6.8 mm
3.00 ct	10.5 × 7.5 mm

Pear Size Chart

Carat Weight	Standard MM Dimensions (Length × Width)
0.25 ct	5.0 × 3.5 mm
0.50 ct	6.8 × 4.5 mm
0.75 ct	7.5 × 5.0 mm
1.00 ct	8.5 × 5.5 mm
1.25 ct	9.0 × 5.8 mm
1.50 ct	9.5 × 6.2 mm
2.00 ct	10.5 × 7.0 mm
3.00 ct	12.0 × 8.0 mm

Emerald Size Chart

Carat Weight	Standard MM Dimensions (Length × Width)
0.25 ct	4.3 × 3.0 mm
0.50 ct	6.0 × 4.0 mm
0.75 ct	6.5 × 4.5 mm
1.00 ct	7.0 × 5.0 mm
1.25 ct	7.3 × 5.3 mm
1.50 ct	7.5 × 5.5 mm
2.00 ct	8.5 × 6.5 mm
3.00 ct	9.5 × 7.5 mm

Princess Size Chart

Carat Weight	Standard MM Dimensions (Length × Width)
0.25 ct	3.5 × 3.5 mm
0.50 ct	4.5 × 4.5 mm
0.75 ct	5.0 × 5.0 mm
1.00 ct	5.5 × 5.5 mm
1.25 ct	6.0 × 6.0 mm
1.50 ct	6.5 × 6.5 mm
2.00 ct	7.0 × 7.0 mm
3.00 ct	8.0 × 8.0 mm

Cushion Size Chart

Carat Weight	Standard MM Dimensions (Length × Width)
0.25 ct	3.5 × 3.5 mm
0.50 ct	4.5 × 4.5 mm
0.75 ct	5.0 × 5.0 mm
1.00 ct	5.5 × 5.5 mm (Square) / 6.0 × 5.0 mm (Elongated)
1.25 ct	6.0 × 6.0 mm
1.50 ct	6.5 × 6.5 mm
2.00 ct	7.2 × 7.2 mm
3.00 ct	8.2 × 8.2 mm

Heart Size Chart

Carat Weight	Standard MM Dimensions (Length × Width)
0.25 ct	4.0 × 4.0 mm
0.50 ct	5.2 × 5.2 mm
0.75 ct	6.0 × 6.0 mm
1.00 ct	6.5 × 6.5 mm
1.25 ct	7.0 × 7.0 mm
1.50 ct	7.5 × 7.5 mm
2.00 ct	8.0 × 8.0 mm
3.00 ct	9.0 × 9.0 mm

Asscher Size Chart

Carat Weight	Standard MM Dimensions (Length × Width)
0.25 ct	3.25 × 3.25 mm
0.50 ct	4.5 × 4.5 mm
0.75 ct	5.0 × 5.0 mm
1.00 ct	5.5 × 5.5 mm
1.25 ct	6.0 × 6.0 mm
1.50 ct	6.5 × 6.5 mm
2.00 ct	7.0 × 7.0 mm
3.00 ct	8.0 × 8.0 mm

Radiant Size Chart

Carat Weight	Standard MM Dimensions (Length × Width)
0.25 ct	4.3 × 3.0 mm
0.50 ct	6.0 × 4.0 mm
0.75 ct	6.5 × 4.5 mm
1.00 ct	7.0 × 5.0 mm
1.25 ct	7.3 × 5.5 mm
1.50 ct	7.5 × 5.8 mm
2.00 ct	8.0 × 6.5 mm
3.00 ct	9.0 × 7.0 mm

Half Moon Size Chart

Carat Weight (Per Stone)	Standard MM Dimensions (Length × Width)
0.15 ct	3.8 × 2.6 mm
0.25 ct	4.5 × 3.0 mm
0.35 ct	5.0 × 3.3 mm
0.50 ct	5.8 × 3.8 mm
0.75 ct	6.5 × 4.3 mm
1.00 ct	7.2 × 4.8 mm

Carat Weight vs. Price Tier Guide

Carat Weight Tier	Indian Trade Terminology	Natural Diamond Price Range (INR)	Lab-Grown Diamond Price Range (INR)	Relative Visual Surface Area Gain
0.30 ct	30 Cents / 30 Pointers	₹30,000 – ₹80,000	₹8,000 – ₹18,000	Base reference
0.50 ct	50 Cents (Half Carat)	₹70,000 – ₹2,00,000	₹15,000 – ₹35,000	+40% face-up area vs 0.30 ct
0.75 ct	75 Cents / 75 Pointers	₹1,20,000 – ₹3,50,000	₹25,000 – ₹55,000	+25% face-up area vs 0.50 ct
1.00 ct	1 Carat (100 Cents)	₹2,00,000 – ₹7,00,000+	₹35,000 – ₹90,000	+30% face-up area vs 0.75 ct
1.50 ct	1.5 Carats (150 Cents)	₹4,50,000 – ₹12,00,000+	₹65,000 – ₹1,50,000	+25% face-up area vs 1.00 ct
2.00 ct	2 Carats (200 Cents)	₹7,00,000 – ₹20,00,000+	₹1,00,000 – ₹2,50,000	+22% face-up area vs 1.50 ct
3.00 ct	3 Carats (300 Cents)	₹15,00,000 – ₹50,00,000+	₹2,00,000 – ₹4,50,000+	+20% face-up area vs 2.00 ct

Where the chart stops working: the density problem

Here is the part almost no size chart addresses, and it is the part that matters most to anyone shopping demi-fine jewellery in India.

Every chart above is calibrated to diamond, which has a density of 3.52 grams per cubic centimetre. Change the material and the entire chart shifts, because carat measures weight and different materials weigh different amounts at the same size.

Moissanite has a density of 3.21. It is about 8.8% lighter than diamond. A Moissanite cut to exactly 6.5mm weighs around 0.91 ct, not 1.00 ct.

Cubic zirconia has a density of roughly 5.7. It is about 62% heavier than diamond. A CZ cut to exactly 6.5mm weighs around 1.62 ct.

The practical consequence appears when a listing quotes true carat weight rather than size:

Stone described as "1.00 carat"	Actual diameter
Diamond, natural or lab-grown	6.50 mm
Moissanite, true weight	about 6.69 mm
Cubic zirconia, true weight	about 5.39 mm

A cubic zirconia sold honestly at one carat of actual weight measures about 5.4mm. That is more than a millimetre narrower than a one carat diamond, and roughly 31% less surface area facing up. It is a visible difference, not a subtle one. Nobody has lied. The number is correct. The chart the buyer applied was simply built for a different material.

This is why the responsible trade convention is to sell simulants by millimetre. Some sellers use Diamond Equivalent Weight, written as DEW, which describes the diamond carat weight a stone visually matches rather than what it weighs. A 6.5mm Moissanite is commonly listed as 1.00 ct DEW even though it truly weighs about 0.91 ct. DEW is a size statement dressed as a weight statement.

When a listing gives you a carat figure for a non-diamond stone and does not specify whether it is actual weight or DEW, that number is genuinely ambiguous. Ask for millimetres. It removes the ambiguity entirely.

Worth stating plainly, because Indian marketplace listings blur it constantly: Moissanite and cubic zirconia are not diamonds. Moissanite is silicon carbide. Cubic zirconia is zirconium dioxide. Both are legitimate, attractive, durable stones with their own optical character, and neither needs to borrow the word diamond to justify itself. Listings that read "Moissanite diamond" or "CZ diamond simulant diamond" are describing two different materials with one word, and that is precisely the confusion that sends a buyer to a diamond size chart with a non-diamond stone in mind.

KYMEE uses Moissanite only in mini and accent form, with cubic zirconia for larger centre stones, all set in 18K gold vermeil over nickel-free 925 sterling silver. If you are matching a KYMEE piece against the charts above, read the millimetre figure and use the diamond column as your visual reference, not the carat figure.

Sizes for the pieces that are not rings

Ring solitaires dominate size chart content, but most stone buying in India is not a solitaire ring. Studs, pendants and tennis bracelets follow different logic entirely, because the reference frame is not a finger.

Stud earrings: The workable range for everyday wear sits between 3mm and 6mm.

Stone size	How it reads
2 to 3 mm	Very subtle, suits second and third piercings
4 mm	Small and clean, visible up close
5 mm	The most common everyday size, balanced
6 mm	Clearly noticeable, still wearable daily
7 mm and above	Statement, better for occasions

Two things shift how a stud reads. Bezel settings enclose the stone in metal, so a bezel-set 5mm stone looks slightly smaller than a prong-set 5mm stone even though the stones are identical. And larger studs need thicker posts to stay straight, which affects comfort over a long day. If you wear earrings from morning to night, staying at or under 5.5mm is the more comfortable choice. KYMEE's stud earrings sit mostly in this everyday band, and the wider earrings range covers hoops, drops and threaders where stone size matters less than overall drop length.

Pendants: A pendant hangs against a much larger visual field than a finger, so stones read smaller than the same size would in a ring. A 5mm stone that looks generous on a hand can look modest at the collarbone. Solitaire pendants generally need to run a size larger than the equivalent ring stone to carry the same presence. KYMEE's pendant and necklace ranges and layered necklaces are worth viewing on the neck rather than judging by stone dimension alone.

Tennis bracelets: These are quoted by total weight across all stones, not by individual stone size, which makes carat figures particularly hard to visualise. What actually determines how a tennis bracelet looks is the diameter of the individual stones, typically between 2mm and 3.5mm, and how densely they are set. KYMEE's tennis bracelets sit within the broader bracelets collection.

Reading proportion against your own hand

Size charts are absolute. Hands are not.

A 6.5mm stone on a size 11 Indian finger reads differently from the same stone on a size 16. Indian ring sizes typically run from about 8 to 20 for women, and the same stone shifts perceptibly across that range. As a rough guide, stones between 4mm and 5.5mm sit comfortably on slimmer fingers, 5mm to 6.5mm is balanced on average fingers, and broader fingers can carry 6.5mm and above without the stone looking oversized.

Setting design changes this as much as stone size. A halo of small accent stones around a centre stone can add two to three millimetres of visible sparkle diameter, which is why halo designs consistently read larger than their centre stone alone. KYMEE's halo rings work on this principle. So do toi et moi rings, where two stones share the visual load and cover more finger than either would separately.

A useful physical test before ordering anything online: mark the millimetre measurement on a slip of paper, cut it out, and hold it against your finger, earlobe or collarbone. Screens distort scale badly. Paper does not.

Matching size to how you actually wear it

Indian wear patterns are continuous in a way that changes the calculation. Jewellery worn daily, through cooking, commuting, monsoon humidity and handwashing, faces different demands from jewellery worn six times a year.

For continuous daily wear, smaller and lower is more practical. A 4mm to 5mm bezel-set stone catches on almost nothing. High-set stones above 6.5mm snag on dupattas, sleeves and bags, and every snag loosens a prong slightly. This is a durability question as much as a style one.

For occasion wear, where a piece comes out for weddings, Diwali or Navratri and goes back into storage, larger stones and higher settings make sense because the exposure is limited. Wedding bands and ring sets sit in this category, as do the heavier pieces in mangalsutra.

For stacking, smaller is structurally necessary. Stones above 4mm sit too proud to let bands stack flush, and adjacent rings will grind against a high setting. Stackable rings work best in the 2mm to 4mm range.

Whatever the size, plating longevity depends on care. Body oils, perfume and cleaning products degrade gold vermeil faster than wear does, and KYMEE covers this in how to clean gold jewellery and on its jewellery care page.

A short decision sequence

If you want a working method rather than a table to stare at:

Start with millimetres, not carats. Decide the visible size you want, in millimetres, before looking at any weight figure.

Choose shape second. Elongated shapes give more visible size per unit of weight than compact ones.

Confirm the material third. Diamond, Moissanite and cubic zirconia convert differently, and the carat number means something different in each.

Check the setting last. Bezel reduces apparent size slightly and increases durability. Halo increases apparent size substantially. High prong settings maximise light but catch on things.

If you already know the exact millimetre size, shape and stone you want and cannot find it in a ready collection, KYMEE's customisation service lets you specify stone type, including cubic zirconia, Moissanite and lab-grown, along with metal and design. Lab-grown is worth noting here specifically, because it is chemically and optically a real diamond, which means every chart on this page applies to it literally, with no density conversion required.

FAQs

How many millimetres is a 1 carat diamond?
A well-proportioned one carat round brilliant measures about 6.5mm across. Fancy shapes at one carat vary widely, from about 5.5mm for a princess to about 10mm long for a marquise.

Is a 1 carat Moissanite the same size as a 1 carat diamond?
Not quite. Moissanite is about 8.8% lighter, so a Moissanite of true one carat weight measures slightly larger than a one carat diamond, closer to 6.7mm. Many sellers quote DEW instead, which is a size equivalence rather than a weight, so always confirm which figure is being used.

Is a 1 carat CZ smaller than a 1 carat diamond?
Yes, noticeably. Cubic zirconia is roughly 62% denser, so a CZ weighing a true one carat measures around 5.4mm rather than 6.5mm. This is why reputable sellers list CZ by millimetre size.

What does 30 cents mean in diamonds?
Thirty cents (or points) refers to a 0.30 carat diamond. Formally in international gemology, one carat is divided into 100 points (often referred to colloquially as 'cents' in certain regional markets). A 30-point round brilliant measures roughly 4.3mm.

Does a 2 carat stone look twice as big as a 1 carat?
No. Doubling carat weight increases the visible face-up surface area by roughly 57% to 59% (not 100%), because a significant portion of the additional weight goes into the depth and pavilion of the stone where it cannot be seen from above.

What stud earring size is best for everyday wear?
Between 4mm and 5.5mm suits most people for all-day comfort. Larger stones need thicker posts and can feel heavy after eight or more hours.

Which shape looks biggest for the same carat weight?
Marquise, then oval and pear. These elongated shapes carry less weight in depth and spread wider at the surface.