SI1 vs SI2 Diamond: Which Should You Actually Buy?

What Do SI1 and SI2 Actually Mean?

On the GIA clarity scale, “SI” stands for Slightly Included – the fifth tier down from Flawless, sitting between VS2 (Very Slightly Included) and I1 (Included). It’s split into two sub-grades, SI1 and SI2, based on how visible a diamond’s internal inclusions are under 10x magnification.

The difference between them comes down to the size, number, and placement of inclusions, not a completely different category of diamond. SI1 diamonds tend to have fewer, smaller, and lighter-colored inclusions that are tucked away from the center. SI2 diamonds usually have inclusions that are larger, more numerous, and more likely to sit directly under the table – the part of the diamond you actually look through.

E vs F vs G Color Diamonds

SI1 vs SI2: Side-by-Side Comparison

Real-World Price Difference

Across major retailers, the SI1-to-SI2 price gap on a comparable stone (same shape, color, and cut grade) typically runs 10–15%. For example, a 1.00 ct round, G color, excellent-cut diamond might run roughly $4,500–$5,200 in SI1 versus $3,800–$4,500 in SI2. That gap can widen as carat weight goes up, since larger stones expose more surface area and make inclusions easier to spot – which is exactly why clarity matters more as the diamond gets bigger.

Diamond prices have changed 2025-2026

Does Carat Size Change the Answer?

Yes – carat weight is the biggest variable in this decision. As a diamond gets larger, its table (the flat top facet) gets larger too, and inclusions that would be invisible in a small stone become much easier to spot in a big one.

• Under 1 carat: A well-chosen SI1 or even SI2 can look completely eye-clean. This is the sweet spot for stretching your budget.
• 1–1.5 carats: SI1 is the safer choice. SI2 still works, but only with careful, in-person (or video) inspection.
• Over 1.5–2 carats: Consider stepping up to VS2 or SI1 minimum, especially for step cuts. Inclusions are far more exposed at this size.

4CS Diamond Full Guide

Does Diamond Shape Matter?

Significantly. Brilliant cuts like round, cushion, and princess have many small facets that scatter light and naturally camouflage inclusions – these shapes are far more forgiving of SI1 or SI2 clarity. Step cuts like emerald and Asscher have large, open facets with fewer light-bending surfaces, which means any inclusion is much easier to spot. If you’ve fallen for an emerald or Asscher cut, it’s worth budgeting up to SI1 or even VS2.

So, Which Should You Buy?

Choose SI1 if: you want a diamond over 1 carat, you’re set on a step cut, or you simply want the peace of mind of a more consistently eye-clean stone. The 10–15% premium buys predictability.

Choose SI2 if: you’re buying a brilliant-cut diamond under 1 carat, you’re comfortable reviewing the clarity plot and video carefully, and you’d rather put the savings toward a larger stone, better color, or a nicer setting.

There’s no universally “better” grade here – only a better fit for your specific stone, shape, size, and budget. The biggest mistake buyers make isn’t choosing SI2 over SI1; it’s buying either grade sight-unseen without checking the clarity plot.

Diamond polish and symmetry

Get Expert Help from OM Jewels Inc

At OM Jewels Inc, every SI1 and SI2 diamond we offer is hand-reviewed by our in-house gemologists for eye-clean quality before it ever reaches our catalog – so you never have to guess. We’ll walk you through the clarity plot, show you a real video of the actual stone, and help you balance clarity, cut, and carat to get the most beautiful diamond for your budget.