Calculator — Kitchen & Bath
Countertop Slab Estimator
Whole slabs to order for stone or quartz counters — area-based count checked against the longest run, plus the seam count.
Inputs
Results
Adjust the inputs to see your result.
About this calculator
Stone counters are bought by the slab, and the count is the larger of two constraints: total area divided by usable slab area, or the longest run divided by slab length. This estimator applies both, so a long run that needs a seam is never hidden by a tidy area figure.
What this number means
Stone and quartz counters are bought by the slab, and slab count is not just area divided by slab size. A 46.75 sq ft kitchen fits in two 45 sq ft slabs by area — but if one run is 12 ft long and slabs are 10 ft long, that run alone needs two slabs joined by a seam. The order quantity is whichever constraint is larger: area or longest run.
Usable area is deliberately smaller than the slab\'s gross size. A nominal 120 × 55 in slab is 45.8 sq ft on paper, but edge trimming, fissures and the fabricator\'s cutting margins eat a little of it, so 45 sq ft is the planning figure. Vein-matched or book-matched layouts can need an extra slab beyond this estimate — tell the fabricator before ordering, not after.
The formula
- Counter area = Total length × Depth ÷ 12 (sq ft)
- Area slabs = Counter area ÷ usable slab area, rounded up
- Run slabs = Longest single run ÷ slab length, rounded up
- Slabs to order = the larger of area slabs and run slabs
- Seams = Run slabs − 1 (seams in the longest run)
Worked example
An L-shaped kitchen: 22 ft of counter in total at 25.5 in deep, longest run 12 ft, 45 sq ft usable per slab, 10 ft slab length.
- Counter area: 22 × 25.5 ÷ 12 = 46.75 sq ft
- Area slabs: 46.75 ÷ 45 = 1.04 → 2 slabs
- Run slabs: 12 ÷ 10 = 1.2 → 2 slabs
- Slabs to order: larger of 2 and 2 = 2 slabs
- Seams: 2 − 1 = 1 seam in the 12 ft run
Assumptions and limitations
- Usable slab area (45 sq ft) is a planning figure for a typical 120 × 55 in slab after trimming. Exact slabs vary — confirm the usable area with your fabricator for exotic stone.
- Seam count covers the longest run only. Corner joints in an L-shape and joins between separate runs are fabricator decisions, not extra slab seams, but they are still visible joints to agree on placement for.
- Sink and cooktop cutouts are not deducted: they rarely save a slab, and the cutout pieces are often reused for windowsills or thresholds.
- Backsplash material is not included — a 4 in backsplash strip comes from slab offcuts or a separate allowance.
- Vein matching, book matching or a waterfall edge can add a slab beyond this estimate; discuss the layout with the fabricator before ordering.
Frequently asked questions
Divide the counter area by about 45 sq ft per usable slab, then check the longest run against the 10 ft slab length and take the larger figure. A 22 ft L-shaped kitchen at 25.5 in deep (46.75 sq ft, longest run 12 ft) needs 2 slabs with 1 seam.
Most slabs run about 120 × 55 in — roughly 45.8 sq ft gross, about 45 sq ft usable after trimming. Jumbo slabs (up to 130 × 65 in) exist for long runs but cost more and not every fabricator stocks them.
One seam per run longer than a slab length: a 12 ft run on 10 ft slabs has 1 seam, a 21 ft run has 2. Short runs and islands usually have none. Agree seam placement with the fabricator — ideally away from the sink and the main sightline.
Not necessarily — it depends on area and run length, which is why islands are included in the total length here. A 10 ft island run at 25.5 in deep is 21.25 sq ft, so on its own it fits in 1 slab with 0 seams.
The Countertop Calculator gives the square footage for pricing. This estimator converts that footage into whole slabs to order plus the seam count — the number the fabricator actually asks for.
Almost never. A cutout does not make a slab go further in a useful way, and fabricators usually keep the cutout piece for small jobs. Count full slabs here and treat any cutout reuse as a bonus.