To measure countertops, multiply each section's length by its depth in inches and divide by 144 to get square feet. A standard counter is 25.5 in deep, so a 10 ft run is 21.3 sq ft. Add up every section, count L-shaped corners only once, add the backsplash if it's the same material, then add 10 to 15% waste for stone.
Countertops are priced by the square foot, and the math for a rectangle is simple: length in inches × depth in inches ÷ 144. A 10 ft run is 120 in long. At the standard 25.5 in depth, that's 120 × 25.5 ÷ 144 = 21.3 sq ft.
If you're working in feet, it's length in feet × (depth in inches ÷ 12). Same answer. Our countertop calculator takes the length in feet and the depth in inches, so you can measure the way most people do.
Do this for every separate piece: each wall run, the island, a peninsula, a bar top. Then add them up.
Base cabinets are 24 in deep, and the countertop overhangs the front by about 1 to 1.5 in. That's where the 25 to 25.5 in figure comes from. The overhang keeps drips off the cabinet doors and gives your fingers something to grab.
For an island with stools, the National Kitchen and Bath Association's planning guidelines call for 24 in of width per seat and 15 in of knee space at a standard 36 in counter height (12 in at a 42 in bar height). So a 7 ft island seats three comfortably, and you'd plan roughly 15 in of overhang on the seating side.
This is where most homemade estimates go wrong. If you measure both legs of an L along the wall, from each end into the corner, you count the corner square twice.
Instead, measure the first leg along the wall into the corner. Then measure the second leg from the front edge of the first leg to its end. At 25.5 in deep, the double-counted corner is 25.5 × 25.5 ÷ 144 = 4.5 sq ft. That's not a disaster, but on stone at $60 or more per square foot it adds a few hundred dollars to a quote that isn't real.
Same rule for U-shapes: measure the back wall fully, then both side legs from its front edge. Or add up all the wall lengths and subtract the depth once for each inside corner.
Here's the calculator's formula run for common layouts, using its defaults: 25.5 in depth, a 4 in backsplash, 15% waste and 50 sq ft slabs. Lengths for L and U shapes are measured the non-overlapping way described above.
| Layout | Counter area | 4 in backsplash | Total | With 15% waste | 50 sq ft slabs | Edge (lin ft) |
|---|---|---|---|---|---|---|
| Straight run, 10 ft | 21.3 sq ft | 3.3 sq ft | 24.6 sq ft | 28.3 sq ft | 1 | 12.1 |
| L-shape, 18 ft total | 38.3 sq ft | 6.0 sq ft | 44.3 sq ft | 50.9 sq ft | 2 | 20.1 |
| Galley, two 12 ft runs | 51.0 sq ft | 8.0 sq ft | 59.0 sq ft | 67.8 sq ft | 2 | 28.3 |
| U-shape, 26 ft total | 55.3 sq ft | 8.7 sq ft | 63.9 sq ft | 73.5 sq ft | 2 | 28.1 |
| Island, 7 × 4 ft | 28.0 sq ft | none | 28.0 sq ft | 32.2 sq ft | 1 | 11.0 |
| Island, 8 × 3.5 ft | 28.0 sq ft | none | 28.0 sq ft | 32.2 sq ft | 1 | 11.5 |
Most kitchens fall somewhere between 30 and 70 sq ft of countertop once the island is included. Look at the L-shape row: 50.9 sq ft with waste is just over one slab, so it needs two. That's common. A small change in layout or waste can push you across a slab line, and slabs are bought whole.
A full-height backsplash changes things too. Take the same 18 ft L-shape with an 18 in stone backsplash instead of 4 in. The splash jumps from 6.0 to 27.0 sq ft and the total with waste goes to 75.0 sq ft. Many people tile the wall above a 4 in splash instead; our tile calculator handles that part.
More than you'd think for natural stone, less for everything else.
| Material | Typical waste | Why |
|---|---|---|
| Granite, marble, quartzite | 10 to 15% | Veining has to line up at seams, and stone can crack during cutting |
| Quartz (engineered) | About 10% | Uniform pattern, but cutouts and seams still eat material |
| Butcher block | About 10% | Sold in fixed lengths, so short runs leave offcuts |
| Laminate | 5 to 10% | Cut from sheets, and pattern matching rarely matters |
For our U-shape example, waste changes the order like this: 63.9 sq ft at 0%, 70.3 at 10%, 73.5 at 15% and 76.7 at 20%. It's two slabs in every case, which is the point. For stone, the slab count matters more than the square footage.
There's no single standard, and it varies by quarry and brand. Typical ranges:
Jumbo slabs can save a seam on a long island. A 10 ft island that's 42 in deep won't fit on a standard 120 × 55 in slab with room to spare, but it fits on a jumbo in one piece. Ask your fabricator which sizes they stock and enter that in the slab size field.
Square footage gets you in the ballpark, but a real quote has more lines on it:
If countertops are part of a bigger job, the kitchen remodel cost calculator puts them in context with cabinets, flooring and labor. Our guide to what a kitchen remodel costs breaks down where the money usually goes.
One last tip: your measurements are for budgeting. Once you've picked a fabricator, they'll template the job on site, usually after the cabinets are installed, and that template is what they cut from.
Multiply length by depth in inches and divide by 144. A 10 ft run is 120 in, so at 25.5 in deep it's 120 × 25.5 ÷ 144 = 21.3 sq ft. Measure each section separately, don't double-count corners on L and U shapes, and add the backsplash if it's the same material.
Most kitchens have between 30 and 70 sq ft of countertop, including the island. An 18 ft L-shaped run at 25.5 in deep is 38.3 sq ft before backsplash, and a 7 × 4 ft island adds another 28 sq ft.
Add 10 to 15% waste to your total square footage and divide by the slab size, then round up. With 50 sq ft slabs, 44.3 sq ft plus 15% waste is 50.9 sq ft, so you need two slabs. Seam placement and veining can change this, so confirm with your fabricator.
Kitchen countertops are usually 25 to 25.5 in deep, which covers a 24 in base cabinet plus a 1 to 1.5 in front overhang. Bathroom vanity tops are usually 21 to 22 in deep. Islands vary, often 36 to 48 in.
Only if it's cut from the same material. A 4 in stone backsplash along 18 ft adds 6 sq ft; a full-height 18 in splash adds 27 sq ft. If you're tiling above the counter instead, leave it out and estimate the tile separately.