The 4Cs for Lab-Grown Diamonds: How Cut, Color, Clarity and Carat Work on a Laboratory-Grown Stone

Updated October 20, 2026

The short answer: The 4Cs (cut, color, clarity and carat weight) apply to laboratory-grown diamonds the same way they apply to mined ones, because a laboratory-grown diamond is a diamond. IGI grades lab-grown stones on the familiar scales: color from D to Z, clarity from FL to I3 under 10× magnification, and, for round brilliants, cut from Ideal through Excellent, Very Good, Good and Fair. Carat is weight, not size: one carat is 200 milligrams. The one big exception in 2026 is GIA, which since October 1, 2025 describes eligible colorless and near-colorless lab-grown diamonds as Premium or Standard instead of printing separate color and clarity letters. Use the 4Cs to narrow your search, then compare millimeter measurements and the 360° video of the actual stone to choose.

This guide walks through each C as it appears on a laboratory-grown diamond report and how to use it when you filter one-of-one loose stones. It sticks to what the labs and the FTC publish.

Why the 4Cs apply to lab-grown diamonds at all

The Federal Trade Commission's Jewelry Guides define a diamond by what it is, not where it came from. Under 16 CFR 23.12, "a diamond is a mineral consisting essentially of pure carbon crystallized in the isometric system," with a hardness of 10, a specific gravity of about 3.52 and a refractive index of 2.42. A laboratory-grown diamond meets that definition. What changes is how it must be described: the FTC requires a clear qualifier such as "laboratory-grown" or "laboratory-created" so buyers know the stone is not mined (see 16 CFR 23.25(b) for the parallel rule on gem names).

Because the material is the same, the physical properties that the 4Cs measure are the same too. A lab-grown diamond can have more or less body color, more or fewer inclusions, better or weaker proportions, and any weight. Grading labs that issue full laboratory-grown reports, such as IGI, apply the same scales they use for mined diamonds, and every IGI laboratory-grown report identifies the stone as laboratory-grown.

IGI frames the 4Cs as four separate grades rather than one overall score: a stone "may receive an excellent cut grade while also having a near-colorless color grade and a slightly included clarity grade." Read them together, and remember that a grading report describes quality. IGI is explicit that a report "does not assign a monetary value to a diamond."

Cut: the C that controls sparkle

Cut is the only C a person controls completely. IGI puts it plainly: nature determined the color and clarity of a mined diamond, but people are responsible for the cut. With a laboratory-grown diamond, growth conditions also shape color and clarity, but cut is still the work of the cutter.

What cut means. GIA separates shape (the outline you see from above, like round or oval) from cut, which describes "the arrangement and proportions of the diamond's facets" and how the stone interacts with light. GIA's cut assessment looks at three things for a standard round brilliant:

  • Face-up appearance: brightness (white light reflected back to you), fire (light dispersed into spectral colors) and scintillation (the pattern of light and dark areas and the sparkle as the stone moves).
  • Design: weight ratio (how much weight sits in the stone relative to its diameter) and durability (the risk of damage built into the proportions, such as a very thin girdle).
  • Craftsmanship: polish (the condition of the facet surfaces) and symmetry (how exactly the facets are shaped and placed).

The scales. GIA grades round brilliant cut from Excellent to Poor. IGI's scale for round brilliants runs Ideal, Excellent, Very Good, Good and Fair, and IGI describes Ideal and Excellent together as the top of that scale. IGI's own descriptions: Very Good "reflects... most of the light to the viewer's eyes," while at Good "some light might escape through the bottom as leakage."

Fancy shapes have no overall cut grade. GIA notes that cut grades "are only given to round brilliant cut diamonds because they are the only cut that have standardized facets." Ovals, emeralds, pears, radiants, cushions and other fancy shapes usually show polish, symmetry and proportions on the report, but no single cut grade. For those shapes you judge cut from the length-to-width ratio, the depth and table percentages, and how the stone looks as it turns in the video. Our shape guide covers what to look for in each outline.

How to use it. For a round, the cut grade is the most direct single signal of how the stone will perform in light, which is why IGI's 4Cs page calls cut "often considered the most influential" of the four. Start your round collection search at Ideal or Excellent if sparkle is the priority, then look at polish and symmetry. Two stones with the same cut grade can still differ slightly in proportions, so compare them on video.

Color: how white a white diamond is

What color means. For colorless and near-colorless diamonds, "color" really means the absence of color. GIA explains that color is graded under controlled lighting by comparing the stone to masterstones with established grades, and documented on the D-to-Z scale, "from D for colorless to Z for light" yellow, brown or gray. GIA introduced that scale in 1953 and deliberately started at D to avoid confusion with older A, B and C systems.

The bands. IGI groups the scale this way:

Grades IGI category
D, E, F Colorless
G, H, I, J Near colorless
K, L, M Faint color
N to Z Very light to light color

IGI notes that D is completely colorless and that E and F differ from it in ways that are "barely detectable." Differences between neighboring grades are subtle, and a stone's shape, size and setting metal affect how much color you notice face-up. Brilliant cuts tend to mask a little color; step cuts such as emerald and Asscher show more, which is why GIA's shape guide suggests G or above for those cuts. Our emerald and Asscher guide goes into that in detail.

Fancy color is a different system. GIA describes "fancy color" as a diamond with color outside the normal D-to-Z range, either more saturated yellow or brown than a Z masterstone or a hue other than yellow, gray or brown. Pink, blue, green and orange laboratory-grown diamonds are graded on hue and intensity (for example Fancy, Fancy Intense or Fancy Vivid), not on a letter. Many lab-grown fancy colors involve post-growth treatment, which the report discloses. See our fancy color guide and the fancy color collection.

How to use it. Our white diamonds collection runs from D through H, so every stone there sits in IGI's colorless or near-colorless bands. If the stone will go in white metal and you want an icy look, filter toward D to F. If it will sit in yellow or rose gold, or you want more size for your budget, the G and H end of the range is worth comparing on video side by side with a colorless stone.

Clarity: inclusions, blemishes and what you can see

What clarity means. GIA defines clarity by "the size, location, visibility and number of inclusions or blemishes." Inclusions are internal or surface-reaching characteristics; blemishes are external. Laboratory-grown diamonds have their own characteristics from the growth process, and labs grade them the same way: under 10× magnification. GIA states that clarity, polish and symmetry grading "can only be finalized using a 10x loupe."

The 11 grades. GIA's clarity scale, which IGI also uses, has six categories and 11 grades:

Grade Name GIA description
FL Flawless No inclusions and no blemishes visible at 10×
IF Internally Flawless No inclusions visible, but has blemishes
VVS1, VVS2 Very, Very Slightly Included Inclusions so slight they are difficult for a skilled grader to see
VS1, VS2 Very Slightly Included Inclusions observed with effort, characterized as minor
SI1, SI2 Slightly Included Inclusions are noticeable at 10×
I1, I2, I3 Included Inclusions are obvious and may affect transparency, brilliance and durability

Graders weigh the number, size, relief, nature and location of each characteristic. GIA also notes that "most diamonds you see in jewelry stores fall between VS... and SI" on the scale.

Eye-clean is not a grade. Shoppers often ask for an "eye-clean" stone, meaning no inclusions visible without magnification. That phrase does not appear on GIA or IGI reports. IGI does publish a working definition used in the trade (viewed face-up, in daylight-equivalent light, from about 6 to 12 inches, with 20/20 vision), and notes that round brilliants at VS2 and higher are reliably eye-clean by that definition, while step cuts and rounds over 3 carats should be checked case by case. IGI's 4Cs page adds that many diamonds with minor inclusions look eye-clean, because visibility depends on size, location, number and viewing conditions.

How to use it. Clarity is where the 360° video does the most work. A VS2 with a small crystal near the girdle can look cleaner face-up than a VS1 with a mark under the table. Open the report, look at the clarity plot when there is one, and match it to what you see on video. Our walkthrough on how to read an IGI lab-grown diamond report shows where the plot and comments sit on the page.

Carat: weight, not size

What carat means. GIA: "Carat measures weight, not size. A metric carat is defined as 200 milligrams." Each carat divides into 100 points, so a 0.25 carat stone is a "twenty-five pointer," and reports usually state weight to the hundredth of a carat.

Why size and weight differ. Two stones of the same weight can face up differently. IGI notes that stones with the same carat weight "may appear different in size depending on their proportions and cut quality." A deep stone carries more weight below the girdle where you cannot see it; a shallow one spreads more of its weight across the top, though very shallow stones can lose brightness. Shape matters too: elongated shapes like oval, pear and marquise look larger from above than a round of the same weight.

That is why we measured real stones. Using the measurements printed on IGI and GIA reports in our catalog, the median 1 carat round measured 6.48 mm across and the median 2 carat round 8.15 mm when we built our carat-to-mm size chart on October 11, 2026. Doubling the weight added about a quarter to the diameter, not double.

Popular weights. GIA notes that 1.00, 1.50 and 2.00 carats are popular "magic sizes," even though "it is difficult to visually distinguish a 0.99 carat diamond from a 1.00 carat." If you are flexible, compare stones just under those marks with stones just over them, on millimeters.

How to use it. Shop by size band (under 1 carat, 1 to 1.99 carats, 2 to 2.99 carats, 3 to 4.99 carats or 5 carats and up), then compare length and width from the report. As stones get larger, color and inclusions are easier to see, so the other three Cs matter more.

What changed at GIA in 2025, and what it means for the 4Cs

On October 1, 2025, GIA launched updated laboratory-grown diamond services. For eligible D-to-Z laboratory-grown diamonds, GIA now issues a Quality Assessment that describes the stone as Premium or Standard based on an overall look at clarity, color and cut, rather than printing separate color and clarity letters. GIA said it would no longer use the nomenclature created for natural diamonds to describe a manufactured product.

What this means in practice:

  1. IGI lab-grown reports still show each C separately. If you want to filter on individual color, clarity and cut grades, IGI-graded stones make that straightforward.
  2. A newer GIA lab-grown document gives a category, not four grades. Premium is a narrow top band and Standard a wider one, each defined by GIA's published thresholds. There is no reliable chart that converts Premium or Standard into a single color and clarity letter, so don't invent one.
  3. Older GIA lab-grown reports with full letter grades remain valid. Some stones in our catalog carry them. Read those grades normally and verify the report number on GIA's site.

Our GIA vs IGI guide sets out GIA's Premium and Standard criteria in full and shows how to compare stones across the two formats.

What the 4Cs don't tell you

The 4Cs are the core of a grading report, not the whole picture. Also check the growth method (CVD or HPHT; see our CVD vs HPHT guide), any treatment comment (what "as grown" and "post-growth treatment" mean), the measurements and proportions, the report number and inscription on the lab's own site, and the actual stone on video. Two stones with identical grades are still different diamonds.

A 4Cs checklist for shopping loose lab-grown diamonds

  1. Pick the shape first. It decides whether there is a cut grade and how much color and clarity show.
  2. Set a carat band, then compare millimeters. Weight is what the report states; size is what you see.
  3. For rounds, start with cut. Ideal or Excellent on an IGI report, then check polish and symmetry.
  4. Choose a color range for your metal and taste. D to F for colorless, G and H for near colorless; compare both on video if you're unsure.
  5. Choose clarity by what you can see. Use VS2 as a starting filter for brilliant cuts, raise it for step cuts and large stones, and confirm on video and the clarity plot.
  6. Verify the report on IGI's or GIA's site and read the comments.
  7. Ask before you buy. All sales are final, so settle any questions first. Our online buying checklist puts the verification steps in order, and you can contact us about any specific stone.

Every stone in our full catalog links to its independent IGI or GIA report, and most have a 360° video. We sell loose stones only, so bring the report number and measurements to your jeweler when you plan the setting.

Frequently asked questions

Are lab-grown diamonds graded on the same 4Cs as mined diamonds? Yes, at labs that issue full laboratory-grown reports, such as IGI: color on D to Z, clarity on FL to I3 under 10×, cut on IGI's Ideal-to-Fair scale for rounds, and carat by weight. Since October 1, 2025, GIA's service for eligible D-to-Z lab-grown stones uses Premium or Standard instead of separate color and clarity letters.

Which of the 4Cs matters most for a lab-grown diamond? It depends on the stone and your priorities. IGI says cut is often considered the most influential C for appearance, because it controls brightness, fire and scintillation. For step cuts, color and clarity show more; for large stones, all three grades become easier to see.

What clarity is eye-clean in a lab-grown diamond? "Eye-clean" is not a grade. IGI's working definition says round brilliants at VS2 and higher are reliably eye-clean, while step cuts and rounds over 3 carats should be checked case by case. Confirm on the video and the clarity plot.

Why don't oval or emerald lab-grown diamonds have a cut grade? GIA gives overall cut grades only to round brilliants, because they are the only cut with standardized facets. For fancy shapes, use polish, symmetry, proportions and the video.

How big is a 1 carat lab-grown diamond? Carat is weight (200 mg), not size. In our catalog, the median 1 carat round measured 6.48 mm across. Elongated shapes look larger at the same weight.

Sources

Reviewed October 2026 against the sources above. Lab services and report layouts change, so verify the report number on the lab's site and watch the current video for any stone you consider.

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