How much countertop do you need?

How do I measure for countertops?

Measure each straight run along the wall in inches, and the depth from the wall to the front edge. Most kitchen base cabinets are 24 inches deep and the counter overhangs them by about 1½ inches, so most counters are 25 to 25½ inches deep. For an L-shaped counter, let one run go all the way into the corner and start the other one after it, so the corner is not counted twice.

How do I calculate countertop square footage?

Multiply the length by the depth in inches and divide by 144. A 120 inch run that is 25½ inches deep is 120 × 25.5 = 3,060 square inches, or 21.25 square feet. A 4 inch backsplash along the same run adds 120 × 4 = 480 square inches, or 3.33 square feet.

How many slabs do I need?

Divide the total area, with some extra, by the area of one slab and round up. A 120 × 56 inch slab is 46.7 square feet. A kitchen with that 120 inch run, its backsplash and a 72 × 36 inch island comes to 42.6 square feet; with 10% extra it is 46.8, just over one slab, so plan on two. The fabricator lays the pieces out on the slabs, so this is the minimum.

What if a counter is longer than the slab?

Then it needs a seam. Slab sizes differ by brand and stone, so ask your supplier; the calculator flags any piece longer than the slab length you enter. Fabricators place seams where they are least visible, often at a sink or cooktop.

Is the sink cutout subtracted?

Usually not. The top is cut from the full slab, so fabricators price the whole area and often add a charge for each cutout. Enter your installed price per square foot to see the total for the area.

How do I avoid counting the corner twice?

On an L-shaped counter the two runs overlap in a square where they meet. Take the first run along its full wall length and start the second after the first one's depth. In the example below, a 72 inch second wall counts as 72 − 25.5 = 46.5 inches. Entering 72 instead would count the corner twice and add 5.22 square feet, including its backsplash.

How much extra material should I allow?

Fabricators nest the pieces on the slab and need room for cuts and for matching the pattern, so the area of the top is a minimum. The example needs 31.65 square feet; with 15% extra that is 36.40 square feet against 46.7 square feet in a 120 × 56 inch slab, so the count is 1 slab on paper; ask the fabricator for the layout before you order.

What the calculator measures

The area of each run is length × depth, and the backsplash is length × height. The result is the surface to be cut from stone, quartz, laminate or solid surface. It does not subtract the sink or cooktop cutouts, because the cutout piece comes out of the same slab and is usually wasted, and because fabricators quote the material by the full piece. The slab count divides the total area, with your waste allowance, by the area of one slab and rounds up.

Worked example: an L-shaped kitchen with a 4 inch backsplash

One wall is 108 inches long and the other 72 inches, so after the corner adjustment the second run is 46.5 inches. The tops are 108 × 25.5 = 2,754 and 46.5 × 25.5 = 1,186 square inches, 3,940 in all, or 27.36 square feet. A 4 inch backsplash along both runs adds 618 square inches, 4.29 square feet, for a total of 31.65 square feet. A 120 × 56 inch slab is 46.7 square feet, so the job needs 1 slab with no allowance and 1 with 15% extra.

Common mistakes

Measuring the cabinets instead of the walls and the finished depth is the first error; add the overhang at the front and any end overhang beside a dishwasher or range. The second is counting the corner twice. Third, a counter that is longer than the slab needs a seam, and where the seam goes affects the look and the strength around a sink. Fourth, estimating the number of slabs from area alone ignores veining or pattern matching, which can leave large offcuts. Treat the figure as a planning minimum and let the fabricator do the layout from a template.

Sources: the areas are standard rectangle arithmetic (length times depth, and length times backsplash height) in square inches, divided by 144 for square feet. Slab sizes, cabinet depths and overhangs vary by supplier and design, so confirm them with your fabricator. Related: square footage calculator, tile calculator, cabinet door calculator and flooring calculator.