Countertops are priced by the square foot: multiply each run's length by its depth in inches and divide by 144. A 10 ft counter at the usual 25½ in depth is 21.25 sq ft; an L-shaped kitchen of 10 ft and 8 ft with a 6 × 3 ft island and a 4 in backsplash comes to 57.7 sq ft, which fits on two 128 × 64½ in quartz jumbo slabs with one seam. The calculator adds up the pieces, lays them out on your slab size and counts the seams, edge and cutouts a fabricator will quote.
How countertop square footage is calculated
Each piece is a rectangle, so the area is length × depth. The trap is the corner: in an L or U, the corner square belongs to only one run. The calculator takes the first wall's full length and shortens the other runs by the counter depth before multiplying.
sq ft = (wall 1 × depth + (wall 2 − depth) × depth + island length × island depth + backsplash run × height) ÷ 144
Measure each run along the wall, into the corner, in inches if you can. Cutouts for the sink and cooktop are not subtracted: the stone is bought and cut as a full piece, and fabricators price cutouts separately.
Worked example: an L-shaped kitchen with an island
The calculator opens on this kitchen, with a 25½ in depth and a 4 in backsplash:
- Wall 1: 10 ft × 25½ in = 21.25 sq ft.
- Wall 2: (8 ft − 25½ in) = 5 ft 10½ in × 25½ in = 12.48 sq ft.
- Island: 6 ft × 36 in = 18 sq ft.
- Backsplash: 10 ft + 8 ft = 18 ft along the walls × 4 in = 6 sq ft.
- Total: 21.25 + 12.48 + 18 + 6 = 57.7 sq ft, 51.7 of it countertop.
- Edge profile: the front of wall 1 (10 ft − 25½ in) plus the front of wall 2 (8 ft − 25½ in) plus the island's 18 ft perimeter = 31 ft 9 in.
- One seam where the two wall pieces meet, and two slabs: the island and wall 1 share the first, wall 2 goes on the second, and the backsplash is cut from the offcuts of both.
With a quote of $60 per sq ft installed, 57.7 × $60 comes to about $3,464. Put your own fabricator's price in the price field; this page does not guess one.
Quartz and granite slab sizes
Engineered quartz comes in fixed sizes. Caesarstone lists its Jumbo slab at 128 in × 64½ in (±1.5%), in 20 or 30 mm. MSI sells prefabricated quartz tops at 108 × 42 in and 112 × 26 in in 2 cm, sized for a single run or an island without a full slab.
| Slab | Size | Good for |
|---|---|---|
| Quartz jumbo (Caesarstone) | 128 × 64½ in | Two counter runs side by side, or an island and a run |
| Prefab quartz (MSI) | 108 × 42 in | An island up to 9 ft |
| Prefab quartz (MSI) | 112 × 26 in | One counter run up to 9 ft 4 in |
Granite and marble slabs are cut from quarry blocks, so their size changes from slab to slab. Pick Your slab size and enter the slabs you tag at the yard.
How many slabs and seams
The calculator splits any run longer than the slab into equal pieces (each split is a seam) and lays the pieces on the slabs deepest first, with a ½ in saw allowance between cuts; the backsplash is then cut in strips from the remnants, since joints in a backsplash are easy to hide. A straight 14 ft run is longer than a 128 in slab, so it becomes two 7 ft pieces with one seam. An L-shaped top has one seam at the corner, a U-shape two. The slab layout drawing shows what goes where. Real layouts follow the veining and skip flaws, so a fabricator sometimes needs one more slab than this estimate.
U-shaped and straight counters
A U-shaped kitchen with an 8 ft left leg, a 10 ft back wall and an 8 ft right leg, all 25½ in deep, is 21.25 + 12.48 + 12.48 = 46.2 sq ft of top, with two corner seams and 17 ft 6 in of front edge. A straight run is simply length × depth; set exposed ends if the counter stops in the open instead of at a wall or appliance, since each exposed end gets the edge profile too.
Counter depth, backsplash and overhang
Countertops typically run 25 to 26 in from front to back, so the edge overhangs the cabinet doors; the calculator starts at 25½ in. Islands with seating are deeper; enter the full island depth including the overhang. A 4 in backsplash strip is usually cut from the same slab; a full-height backsplash up to the wall cabinets is often tile instead, which the backsplash tile calculator works out.
Edge profile and cutouts
Fabricators charge edge profiles by the linear foot on every exposed edge: the front of each wall run, exposed ends and the whole perimeter of an island. Sink and cooktop cutouts are counted separately because each is priced per cutout.
What to work out next
- Seal the joint between the counter and the backsplash or wall: the caulk calculator.
- A tiled backsplash or tiled counters: the tile calculator.
- The whole kitchen budget, cabinets to counters: the kitchen remodel cost calculator.
- All floor, tile and countertop tools: floors, tile and countertop calculators.