You are looking up the price of a 1 carat lab-grown diamond. You find tables in dollars, wide ranges and no clear answer. The problem is not a lack of information. It is that you are quoted the price of a loose stone, when what you are buying is a ring. Here are both figures, and the gap between them.

A carat is a weight, not a size

First, a common confusion to clear up. The carat measures mass, not diameter. One carat equals 0.2 grams.

On a round brilliant-cut diamond, one carat corresponds to a diameter of roughly 6.5 millimetres. Keep that figure in mind: it will spare you a few surprises when the parcel arrives.

And weight does not tell you everything about the visual effect. Two one-carat stones can look very different depending on their shape. An elongated cut, such as a pear or a marquise, shows more visible surface than a round stone of the same weight, because its material is spread out differently. On the same budget, that is a real lever.

Lab-grown diamond prices, carat by carat

Here are the ranges seen in 2026 for certified loose stones with good colour and clarity. They are orders of magnitude, not price lists.

Weight	Approximate diameter	Loose stone range
0.50 carat	5.2 mm	€200 to €500
0.75 carat	5.9 mm	€350 to €700
1.00 carat	6.5 mm	€600 to €1,200
2.00 carats	8.1 mm	€1,200 to €2,500
3.00 carats	9.3 mm	€1,800 to €3,500

One point the price tables always leave out. Prices do not rise in a straight line, but they do not double at every step either, as they do with natural stones. On the lab-grown market, going from 1 to 2 carats costs proportionally far less than on the natural market. That is where the real advantage of these stones lies.

Why prices have fallen by more than 70% since 2020

Three reasons, and none of them is a trick.

Production capacity has exploded. Growing reactors have multiplied, above all in India and China. More supply, the same demand, falling prices. It is ordinary economics.

The processes have improved. Growth cycles are shorter, yields are better and there is less waste. The cost of producing a stone has melted away.

Competition has set in. The market has become competitive, whereas the natural diamond market remains highly concentrated upstream.

A one-carat stone that cost several thousand euros five years ago now sells for a fraction of that price. That is excellent news when you buy.

Let us also mention the downside, because nobody else does. This drop crushes resale value. A lab-grown diamond is practically impossible to sell back, and there is no organised secondary market for these stones. Buy one to wear it, never as an investment.

What changes the price at the same weight: the 4Cs

Two one-carat stones can differ in price by a factor of two. Four criteria explain the gap.

Colour. It is graded from D, colourless, to Z, distinctly yellow. On a white diamond, the eye can barely tell D from G. Paying for a D when an F or a G looks the same means paying for a letter on a certificate.

Clarity. It describes internal inclusions. Above VS2, nothing is visible to the naked eye any more. VVS and FL grades cost more without changing anything you see on the finger.

Cut. This is the one criterion where you should never cut corners. A mediocre cut dulls a perfect stone. An excellent cut makes an average stone sparkle. Always aim for Excellent or Very Good.

Carat weight. The carat, in other words. A useful tip: a 0.90 carat stone costs noticeably less than a 1.00 carat stone, while the difference in diameter is about 0.2 millimetres. Nobody can see it. That round number comes at a high price.

One last point that is not part of the 4Cs but matters just as much: the certificate. A serious lab-grown diamond comes with an IGI or GIA report and a number laser-inscribed on the girdle of the stone. Without a certificate, you have no way of checking what you are buying. Our article on the price of a diamond covers each criterion in detail.

From loose stone to finished ring: where the rest of the budget goes

This is the point that price tables never address, and yet it is the one that matters to you.

Between the loose stone and the ring that arrives at your door, there is a lot of work. Designing the setting. Casting the metal. Filing and polishing. Stone setting, which takes hours and calls for a very steady hand. Quality control. Hallmarking. Then the box, insured shipping, the guarantee and after-sales service.

And then there is the metal. The same stone mounted in 925 silver, vermeil or recycled 18-carat gold gives three very different prices. The number 750 stamped on an 18-carat gold piece stands for 750 thousandths of fine gold, and that material is expensive: our article on the 750 hallmark explains it.

This is why a ring set with a one-carat diamond never costs the price of the stone alone. An €800 stone does not make an €800 ring. Any listing that suggests otherwise is hiding something: the metal, the setting or the certificate.

The gap with a 1 carat natural diamond

A natural one-carat diamond of comparable quality sells for several thousand euros. The gap with lab-grown is measured in multiples, not percentages.

Physically, the two stones are identical. Same composition, same crystal structure, same hardness of 10 on the Mohs scale, same brilliance. A gemmologist can tell them apart with specialised equipment, by reading the traces left by the way they grew. Nobody can tell them apart by eye, on the finger or in a photo.

The difference lies in origin and rarity. A natural diamond formed hundreds of millions of years ago and was mined. A lab-grown diamond was grown. Some people value that geological history, and that is entirely legitimate. Others prefer to put the price difference into the setting, the metal or elsewhere.

A useful note about the pocket testers sold online: they measure thermal conductivity. Since a lab-grown diamond is a real diamond, they display “diamond” in both cases. They do not identify the origin; they only rule out imitations such as cubic zirconia.

How to spend your stone budget wisely

Five decisions make the difference, in this order.

One. Do not pay for the round number. A 0.90 or 0.95 carat stone costs noticeably less than a 1.00 carat one, for an almost identical diameter.

Two. Go down to F or G colour rather than D. On a yellow gold setting, you can go even lower without it showing.

Three. Go down to VS clarity. What you cannot see with the naked eye is not worth paying for.

Four. Never compromise on cut. Cut is what creates the light.

Five. Think about shape. A pear or a marquise looks larger than a round stone of the same weight, and it lengthens the finger. If the look matters more than the figure on the certificate, that is where to look.

And think about the metal before the carat. A beautiful stone in a 925 silver setting costs less than an average stone in gold, and it can look better. Our article on silver engagement rings weighs up this trade-off frankly. And if you are going for a coloured stone, the choice of setting changes everything about the result.

Key takeaways

A certified one-carat lab-grown diamond of good quality, sold as a loose stone, costs around €600 to €1,200 in 2026. Its price has fallen by more than 70% since 2020, for simple industrial reasons.

But that figure is not the price of a ring. Between the stone and the finished piece come the metal, the setting, quality control and the guarantee. That is what you are really paying for, and that is normal.

Two final tips. Do not pay for decimals nobody can see: the round-carat threshold, the letter D, VVS clarity. And do not buy a lab-grown diamond with resale in mind: it does not resell. It is made to be worn.

Browse our lab-grown diamond earrings, or write to us about a bespoke project. We are happy to start from a budget rather than a carat weight.

FAQ

How much does a 1 carat lab-grown diamond cost?

In 2026, a certified one-carat loose stone with good colour and clarity costs around €600 to €1,200. That price is for the stone alone. A finished ring costs more, because it includes the metal, the setting and the guarantee.

How big is a one-carat diamond?

About 6.5 millimetres in diameter for a round brilliant cut. The carat measures weight, 0.2 grams, not size. An elongated stone of the same weight looks larger on the finger.

Why have lab-grown diamonds become so cheap?

Because production capacity has risen sharply, growing processes have improved and the market has become competitive. Prices have fallen by more than 70% since 2020.

Is a lab-grown diamond a real diamond?

Yes. Same chemical composition, same crystal structure, same hardness of 10 on the Mohs scale. The only difference is its origin: it is grown rather than mined.

Does a lab-grown diamond lose value?

On resale, yes, heavily. There is no organised secondary market, and the falling price of new stones crushes the value of second-hand ones. It is a stone to buy to wear, not to resell.

Do you need a certificate for a lab-grown diamond?

Yes. Insist on an IGI or GIA report, with a number laser-inscribed on the girdle of the stone. Without a certificate, nothing proves the stated weight, colour, clarity or cut quality.

Is it better to buy 1 carat or two 0.50 carat stones?

It depends on the piece. On a solitaire ring, a single one-carat stone has far more presence. On earrings or a three-stone ring, several small stones cost less for the same total weight and give a beautiful result.

Fiona