What Are SI Diamonds?

SI stands for Slightly Included. It's the fifth clarity tier on the GIA's 11-grade clarity scale, sitting below VS2 and above the Included (I) grades. SI clarity diamonds contain inclusions — internal characteristics — that are clearly visible under 10x magnification, and in some cases faintly visible to the naked eye depending on their size, type, and position within the stone.

This is the single most important question for any SI diamond buyer, and the honest answer is: it depends on the specific stone, not just the grade.

SI1 diamonds usually pass the eye-clean test — meaning when viewed face-up at a normal 6 to 12 inch distance, the inclusions are not visible without magnification. The inclusions in SI1 stones tend to be smaller, fewer, and positioned in less central or less conspicuous locations than in SI2 diamonds.

SI2 diamonds are far less consistent. Some SI2 stones are genuinely eye-clean and indistinguishable from a higher grade once mounted. Others have inclusions visible to the naked eye, particularly in larger carat weights or in shapes that expose the diamond's interior more directly. SI2 is often described in the trade as the most "buyer beware" clarity grade — not because the stones are poor quality, but because the variation within the grade is wide enough that the label alone doesn't guarantee an eye-clean result.

There is no official, universally agreed clarity threshold for "eye-clean" — it's a practical term referring to how a diamond looks under normal viewing conditions to an average observer. SI1 diamonds clear that bar in the large majority of cases. SI2 diamonds clear it often, but not reliably enough to buy on the grade label alone.

The difference between SI1 and SI2 comes down to the size, number, and visibility of inclusions — not a different category of flaw, just more of it and more visible.

SI1 diamonds typically have inclusions that are only visible under magnification, and the placement tends to be less central, less severe, and less likely to interfere with the diamond's appearance or light performance. SI1 is generally the safer, more dependable choice for buyers who want a high likelihood of an eye-clean stone without paying the premium of VS2 or higher.

SI2 diamonds have more noticeable inclusions — generally larger and more numerous than in SI1 — that are more likely to be visible without magnification, particularly in larger stones or shapes that show the interior of the diamond more openly. SI2 inclusions are also more likely to sit in the periphery near the girdle rather than centrally under the table, which is one reason a seemingly lower-clarity stone can still look perfectly clean when viewed from above.

Common Inclusion Types in SI Diamonds

Both SI1 and SI2 diamonds typically contain some combination of:

• Crystals — small mineral deposits trapped within the diamond during formation
• Feathers — small internal fractures, usually with no impact on durability at this clarity level
• Clouds — clusters of tiny pinpoint inclusions that create a hazy area
• Needles — thin, elongated crystal inclusions

SI1 diamonds generally have fewer and smaller versions of these characteristics compared to SI2 stones of equivalent carat weight.

Price Difference Between SI1 and SI2

The price gap between SI1 and SI2 for comparable diamonds typically runs around 10–15%. For example, a 1.00 carat round, G color, Excellent cut diamond might run roughly $4,500–$5,200 in SI1 versus $3,800–$4,500 in SI2 — meaningful savings for a clarity difference that, in a well-chosen stone, may not be visible at all once the ring is on the hand.

This is the more useful comparison for most buyers, because it's where real money and real visual difference intersect.

VS2 — one grade above SI1 — has inclusions so small and difficult to detect that VS2 diamonds are almost always reliably eye-clean. That added consistency typically comes with a 10–20% price premium over SI1 diamonds of comparable carat, color, and cut.

In many cases, a well-selected SI1 diamond delivers a face-up appearance very similar to a VS2, especially in round, oval, and other brilliant-cut shapes, whose faceting pattern naturally helps mask minor inclusions through the sheer amount of light movement across the stone's surface. For buyers focused on getting the most visual value for their budget, this is precisely the trade-off SI clarity is built around.

The calculation changes for step-cut diamonds. Shapes like the emerald cut and Asscher cut have large, open table facets that act more like a window into the stone, making inclusions considerably easier to spot than they would be in an equivalent brilliant cut. VS clarity or higher is generally recommended for step-cut diamonds specifically — see our guide on Asscher cut vs emerald cut diamonds for more on how shape affects clarity requirements.

SI clarity diamonds cost less than VS stones of comparable carat weight, color, and cut — typically the largest single price drop on the clarity scale relative to the visual change involved. This is exactly why SI diamonds are popular with buyers who want to prioritize carat size or overall budget rather than chasing the highest possible certificate grade.

Carat weight magnifies the visibility of inclusions. A 0.50 carat SI2 diamond may appear completely eye-clean, while a 2.00 carat SI2 diamond of similar relative inclusion characteristics is considerably more likely to show visible flaws, simply because the inclusions themselves — and the facets around them — are larger and more visually significant at greater size.

Cut and shape change how forgiving the grade is. Round, oval, cushion, and other brilliant cuts use many small facets that scatter light and movement across the stone's surface, which naturally helps disguise minor inclusions. Step cuts like emerald and Asscher offer far less concealment.

Color and clarity interact with overall budget. Many buyers choosing SI clarity do so specifically to redirect savings toward a better color grade, a larger carat weight, or a higher-quality cut — all of which have a more consistently visible impact on a diamond's beauty than clarity does at this tier.

Round brilliant: The most forgiving shape for SI clarity. Its 57–58 facets scatter light extensively, and the resulting flashes of brilliance make minor inclusions far harder to spot. Round brilliant is consistently recommended as the best shape for SI clarity diamonds.

Oval, cushion, radiant, marquise, pear: All brilliant or mixed-cut shapes that, like the round, use faceting patterns that help conceal inclusions through light scatter and movement. These shapes remain strong choices at SI clarity.

Princess cut: A brilliant-style cut with good inclusion-masking properties, though slightly less forgiving than round due to its larger, flatter facets near the corners.

Emerald and Asscher cut: The least forgiving shapes for SI clarity. Their large, open step-cut facets expose the diamond's interior directly, making inclusions considerably more visible. If you're set on a step-cut shape, moving up to VS clarity or higher is a reasonable and often necessary investment.

Always start from "eye-clean," not from the grade label. Use SI1 or SI2 as a starting filter, then evaluate individual stones rather than buying on the grade alone.

Review high-resolution or 360-degree imagery before buying. Reputable online retailers provide magnified video or photography of the actual stone you're purchasing, not a stock representative image. This lets you see exactly how visible — or invisible — the inclusions actually are.

Request the clarity plot. Every GIA or IGI certificate includes a clarity plot diagram showing the type, size, and exact location of each inclusion. An inclusion near the girdle, hidden under a prong once set, behaves very differently from one centered directly under the table.

Favor inclusions near the edge over inclusions near the center. Inclusions positioned toward the girdle are easier to mask with a well-chosen setting and are generally less visually disruptive than those sitting centrally beneath the table.

Let the setting do some of the work. Certain settings — particularly bezel settings, which wrap a thin rim of metal around the stone's girdle — can help cover inclusions positioned near the edge of the diamond, while prong settings leave the entire stone fully exposed.

Always buy with GIA or IGI certification. Clarity grading consistency varies meaningfully between labs. An SI1 diamond graded by a less rigorous lab may, in practice, be closer to an SI2 or even an I1 under GIA's stricter standards. For a complete breakdown of certification reliability, read our guide on IGI vs. GIA certified diamonds.

SI clarity is available in both natural and lab-grown diamonds, and grading standards are applied consistently across both — there is no separate, more lenient clarity scale for lab-grown stones. A lab-grown SI1 diamond and a natural SI1 diamond of the same cut, color, and carat weight will look identical, since clarity grading evaluates the same physical characteristics regardless of origin.

Lab-grown SI diamonds typically cost 50–70% less than natural diamonds of equivalent specifications. Since SI clarity is already the budget-conscious choice on the natural diamond scale, combining SI clarity with a lab-grown stone represents one of the strongest value combinations available — particularly useful for buyers who want to put real budget weight behind carat size, color grade, or cut quality instead. Our lab grown vs. natural diamonds guide covers this comparison in full.

SI clarity is the right choice if:

• You're buying a round, oval, cushion, or other brilliant-cut shape
• Your priority is maximizing carat weight or overall value within a budget
• You're comfortable reviewing magnified imagery or a clarity plot before purchasing
• You're buying a diamond under roughly 1.5 carats, where inclusions are naturally less prominent

A higher clarity grade may be worth the premium if:

• You're buying an emerald, Asscher, or other step-cut diamond
• Your diamond is 2 carats or larger, where inclusions become more visually significant
• You want the reassurance of a grade that is reliably eye-clean across nearly every individual stone, without needing to inspect imagery closely
• Resale and long-term value retention are a significant priority

For most buyers purchasing a brilliant-cut diamond under 1.5 carats, a carefully selected SI1 — and often a well-chosen SI2 — delivers a genuinely beautiful, eye-clean diamond at meaningfully better value than the clarity grades above it.