Island size, slab size and seams
Seams on an island are the most visible seams in a kitchen, so most owners want the top in one piece. Whether that is possible depends on the slab:
| Slab | Approximate size | Notes |
|---|---|---|
| Standard quartz | 120 × 56 in | Most colors stocked in this size |
| Jumbo quartz | 130 × 65 in | Fewer colors; helps avoid an island seam |
| Granite and quartzite | Varies by quarry block | Measure the actual slabs before you tag them |
If an island is longer or deeper than the slab, a seam is unavoidable. A good fabricator places it where it is best supported and away from the sink and cooktop cutouts, and on veined stone lays out the template so the vein runs across the seam.
Seating overhang and supports
Industry guidance (the Natural Stone Institute's design manual) limits an unsupported overhang to about 10 inches for 3 cm stone and 6 inches for 2 cm, and never more than a third of the top's width. A seating overhang of about 12 inches is common at standard 36-inch counter height, which is past the 3 cm limit, so it needs support:
- Corbels: visible brackets under the overhang. Simple and inexpensive.
- Hidden steel brackets or flat bar: set into the cabinet top so the overhang looks unsupported.
- Legs or a panel end: for very deep overhangs or a table-style extension.
Supports go in before templating, so decide on seating before the measure.
Waterfall island ends
A waterfall runs the slab down one or both sides of the island to the floor, joined at a mitered 45-degree edge. Done well, the vein continues around the corner. A waterfall end panel typically costs $500 to $2,000 per end, depending on the material and the vein matching. Quartz, quartzite and porcelain are common choices; see countertop edge profiles for how mitered edges are built.
Sink and cooktop islands
Cutouts weaken a slab, so islands with a sink or cooktop need more planning:
- Sink cutout: $0 to $300; the first is often included. Undermount sinks suit stone.
- Cooktop cutout: $100 to $200.
- Keep seams away from cutouts where possible, and have the sink and cooktop specs ready at templating.
- Moving a sink or cooktop into an island means new plumbing, gas or electrical, which can need a permit; a countertop swap alone generally does not.
Island countertop cost
Islands are priced per square foot installed like the rest of the kitchen, plus edges, cutouts and any waterfall:
| Material | Typical installed cost |
|---|---|
| Quartz | $50 to $150 per sq ft (premium to $200) |
| Granite | $50 to $150 per sq ft (exotic to $250) |
| Quartzite | $65 to $200 per sq ft |
| Porcelain | $50 to $120 per sq ft |
These are typical national ranges; a fabricator's written quote for your island is what counts. Some owners use a contrasting material on the island, for example quartzite on the island and quartz on the perimeter. See countertop cost in Sacramento, or tell us about your island and we pass it to a licensed fabricator who serves your city. Regional overview: quartz and granite countertops in Sacramento.
Main guide: quartz and granite countertops in Sacramento.