Countertop square footage calculator

Add each run of countertop, get total square footage plus a slab estimate. Measurements are in inches, the way you take them in the field.

How countertop square footage is actually measured

Square footage is length × depth for each run, converted from inches. A standard kitchen run is 25.5″ deep once you account for the 1½″ overhang past a 24″ base cabinet. Islands are measured on their own because they are usually deeper and often have overhang on more than one side.

Backsplash is billed separately in most shops, but it comes off the same slab, so it belongs in your material math even when it sits on its own line of the quote. A 4″ splash running the full length of your countertop runs adds roughly a third of a square foot per linear foot.

Why the waste allowance matters more than the square footage

The number that decides whether a job is profitable is not finished square footage, it is how much slab you consume to produce it. Sink cutouts, cooktop cutouts, seam alignment on a directional pattern, and the simple geometry of fitting L-shaped runs onto a rectangle all mean you buy more stone than you install.

Fifteen percent is a reasonable default for a straightforward kitchen in a forgiving material. A heavily veined quartzite where the customer expects the pattern to flow across the seam can push past thirty percent, because you are cutting for appearance rather than yield. Set this number from your own history, not from a rule of thumb.

From square footage to slab count

Divide total square footage including waste by usable slab size. Usable is the key word: a slab sold as 55 square feet is rarely 55 usable square feet once you lose the edges. Most shops work from a usable figure they have measured themselves, which is why it is an input here instead of a fixed number.

Always round slab count up. A job that calculates to 1.2 slabs is a two-slab job, and the leftover is a remnant you should be tracking rather than losing in the back of the shop.