What Is the Carat Weight of a Diamond? A Lab-Grown Diamond Guide

By Alex Klimchenko, Sales Expert at Labrilliante · Updated November 2, 2026

A carat is a unit of weight equal to 200 milligrams, and it measures how much a diamond weighs, not how big it looks. That holds for every diamond, including a lab-grown diamond. Each carat is divided into 100 points, so a 0.50 ct stone is 50 points. Carat weight is only one of the 4Cs, which is why two stones of the same weight can differ in look and in price.

According to the Gemological Institute of America (GIA), a metric carat is defined as 200 milligrams. That is a small unit, so the trade also uses a finer scale.

The finer scale is points. GIA states that each carat is subdivided into 100 points. A 0.50 carat diamond is 50 points, and a 0.75 carat diamond is 75 points. Reports and price lists usually write the weight as a decimal followed by "ct", so 1.00 ct is one full carat.

At the counter, this matters. A customer who says "I want a one-carat ring" is naming a weight. Whether that stone looks large or modest on the hand depends on other things, which the next section covers.

GIA puts it directly: carat measures weight, not size. It also notes that bigger isn't always better, because two diamonds of the same carat weight aren't necessarily equal.

Weight describes mass. Size, meaning how wide the diamond looks from above, depends on how the stone is cut and shaped. Two diamonds of identical weight can face up differently because their shape and proportions differ, and value reflects all of the 4Cs (carat, color, clarity and cut), not carat alone.

This helps when you advise a shopper with a fixed budget. Asking "what size do you want it to look?" gets you further than asking for a number of carats. Two stones of the same weight shown side by side make the point faster than any explanation.

A lab-grown diamond is weighed and graded in carats the same way any other diamond is. The unit does not change with origin. What changes is how you search for the stone and what paperwork comes with it.

Labrilliante is a US-based manufacturer and wholesale supplier of lab-grown diamonds, grown by HPHT and CVD methods, serving jewelry retailers and brands since 2017. Our inventory holds 100,000+ loose diamonds, in the shapes listed below. Ask our team for a specific weight and shape.

The shapes in stock are round, oval, pear, emerald, radiant, cushion, princess, asscher, marquise and heart. We also carry colored lab-grown diamonds in yellow, pink, blue and green, plus matched pairs, rare cuts and custom cuts.

On certification, IGI- and GIA-certified diamonds are available, and the inventory includes both certified and non-certified stones. If a customer needs a grading report, ask our team which stones come with one before you quote a stone. Calibrated melee is not certified stone by stone; reports are available on request.

Browse the full catalog at /diamonds or the lab-grown selection at /diamonds/lab-diamonds. Retailers who want wholesale access can start at /wholesale-lab-grown-diamonds. Brands interested in a supply relationship can read about our program at /partnership/become-a-distributor.

Three checks keep a purchase on track.

First, read the weight to two decimals and compare stones at the same weight and shape. A 0.90 ct and a 1.00 ct stone differ by 10 points, and that gap is easy to miss in a listing.

Second, check the shape against the setting. The same weight in a different shape will sit differently in a prong or a bezel, so confirm the shape before you confirm the carat.

Third, look at the whole grade. Carat tells you the weight. Color, clarity and cut tell you what the stone looks like at that weight, and GIA says value reflects all four.

How much is one carat?

One carat is 200 milligrams. GIA defines a metric carat this way. The unit measures weight only. It says nothing about how wide the diamond looks, which depends on shape, cut and proportions.

How many points are in a carat?

There are 100 points in one carat, according to GIA. A 0.25 ct diamond is 25 points, a 0.50 ct diamond is 50 points, and a 1.00 ct diamond is 100 points. Jewelers use points to talk about small differences in weight without writing long decimals.

Does a higher carat weight always mean a bigger-looking diamond?

Not always. GIA says carat measures weight, not size, and that two diamonds of the same carat weight aren't necessarily equal. Shape, cut and proportions change how a diamond looks from above, so compare stones side by side rather than by weight alone.

Is carat weight measured the same way for a lab-grown diamond?

Yes. A lab-grown diamond is weighed in carats like any other diamond, with one carat equal to 200 milligrams and 100 points to the carat. Origin changes how the diamond was formed, and the unit stays the same. At Labrilliante, IGI- and GIA-certified diamonds are available, and some stones in stock are non-certified.

Which lab-grown diamond shapes can I find at Labrilliante?

Our inventory includes round, oval, pear, emerald, radiant, cushion, princess, asscher, marquise and heart shapes, among 100,000+ loose diamonds. We also stock colored lab-grown diamonds in yellow, pink, blue and green. Browse the catalog at /diamonds or ask our team for a specific weight and shape.

Labrilliante is here to help retailers and brands find the right stone at the right weight. Call +1 551-321-8771, email info@labrilliante.com, or write to us at 330 Washington St, Hoboken, NJ 07030.