Backsplash Calculator — Tile, Mastic, Grout and Trim
A backsplash is not a floor. You measure it in linear feet along the counter, not length by width — and the wall behind the range is usually taller than the rest. This handles both.
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How to work it out
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Measure along the wall in linear feet
A backsplash is a band, so it is measured the way trim is: total linear feet of counter that is getting tile. Run the tape along the wall at counter height and add up every stretch — the sink wall, the return by the fridge, the bit beside the range.
Do not measure around the front edge of the counter. The tile goes on the wall behind it, which is shorter than the counter is.
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Measure the height to the cabinets
Standard is 18 inches from the countertop to the underside of the upper cabinets, but it is worth checking rather than assuming — older kitchens and custom cabinets vary, and a two inch difference over a 12 foot run is two square feet.
If there are no upper cabinets on part of the run, decide now where the tile stops. A common choice is to carry it to the same height as the rest and finish the top edge with trim.
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Handle the range wall separately
The wall behind a range or under a hood is almost always taller than the rest — often 30 inches, sometimes all the way to the ceiling. It is also where a feature pattern usually goes.
Enter its width and height in the second pair of boxes. The calculator removes that section from the main run first, so nothing gets counted twice.
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Do not deduct the outlets
A kitchen backsplash has a lot of outlets, and every one means cutting a tile. The cut-off is usually unusable, so subtracting the outlet area leaves you short rather than saving you money.
Leave them in and let the 15% waste allowance do its job. Buy the deeper electrical box extenders at the same time — the tile pushes the outlet face forward and standard screws will not reach.
Backsplash area by counter run
Area in square feet, before waste, at three common heights.
| Counter run | 15 in. high | 18 in. high | 24 in. high |
|---|---|---|---|
| 6 ft | 7.5 | 9.0 | 12.0 |
| 8 ft | 10.0 | 12.0 | 16.0 |
| 10 ft | 12.5 | 15.0 | 20.0 |
| 12 ft | 15.0 | 18.0 | 24.0 |
| 15 ft | 18.8 | 22.5 | 30.0 |
| 20 ft | 25.0 | 30.0 | 40.0 |
| 25 ft | 31.3 | 37.5 | 50.0 |
Add the taller section behind the range on top of this, and then add waste.
Tiles per square foot
Face area in square inches divided by 144.
| Tile | Square inches | Square feet each | Per sq ft |
|---|---|---|---|
| 3 × 6 in. subway | 18 | 0.125 | 8.0 |
| 4 × 4 in. | 16 | 0.111 | 9.0 |
| 2 × 8 in. | 16 | 0.111 | 9.0 |
| 2 × 12 in. | 24 | 0.167 | 6.0 |
| 4 × 12 in. | 48 | 0.333 | 3.0 |
| 6 × 6 in. | 36 | 0.250 | 4.0 |
| 12 × 12 in. mosaic sheet | 144 | 1.000 | 1.0 |
Mosaic is sold by the sheet. One 12 × 12 in. sheet covers a square foot however many little tiles are on it.
How much tile for a 12 foot backsplash?
Twelve linear feet at the standard 18 inch height is 18 square feet. Add a 3 ft wide section behind the range going up to 30 inches and you replace 4.5 sq ft of the main run with 7.5 sq ft, so the total is 21 square feet.
With a 15% allowance that is 24.2 sq ft to buy. In 3 × 6 in. subway tile — eight to the square foot — that is 194 tiles. At 40 per box, five boxes. You will also want one gallon of mastic, one 10 lb bag of grout, and a length of trim for any exposed edge.
Why a backsplash wastes more tile than a floor
A floor is a big open rectangle. Most tiles go down whole and the cuts happen only around the edges, which is why 10% is enough.
A backsplash is the opposite. It is a narrow band, so almost every course meets a boundary. There are outlets to cut around, a window over the sink, the edge of a cabinet, and an end wall. On an 18 inch height with 3 × 6 in. subway you get three courses, and the top course nearly always needs ripping down to fit under the cabinets.
Fifteen per cent is the honest default. Go to 20% for herringbone or a diagonal set, where every tile at every boundary is cut on an angle, and 25% if the tile has a pattern that has to line up across sheets.
Mastic or thinset?
For a dry kitchen wall, premixed mastic in a tub is the easier choice. It grabs quickly, holds tile on a vertical surface without sliding, and there is no mixing. One gallon covers roughly 40 square feet with a 3/16 in. V-notch trowel, which means most backsplashes need a single tub.
Thinset mortar is the right choice in two cases: behind a range or sink where the wall may get genuinely wet, and with any glass, stone or large-format tile. Mastic can stay soft behind non-porous tile and it is not rated for wet areas. White thinset also matters under glass tile, because gray shows through.
Read the tile manufacturer's own instruction sheet before you buy either. Glass and natural stone frequently specify a particular adhesive, and using the wrong one voids everything.
Grout: how much, and which kind
Backsplashes use very little grout. The tile is thin and the joints are narrow, so a single 10 lb bag covers around 50 square feet of standard subway tile at 1/16 in. joints. Most kitchens need one bag.
Joint width decides the type. Under 1/8 in. use unsanded grout — sanded grout will not pack into a narrow joint and the sand can scratch glass and polished stone. At 1/8 in. and over, sanded grout is stronger and shrinks less.
Mosaic sheets are the exception on quantity: all those little joints add up, and a mosaic backsplash can use nearly twice the grout of the same area in subway tile. If you are running mosaic, buy two bags.
The edges nobody plans for
Where the tile runs into a cabinet or turns a corner into a wall, the edge is hidden and you can ignore it. Every other edge is visible, and a raw cut tile edge looks exactly like what it is.
Three ways to finish it. Bullnose tile from the same range has a rounded factory edge — the traditional answer, but many modern tile lines no longer make it. Metal trim, usually an L or square profile in anodized aluminum, goes on before the tile and gives a crisp line. Mitered edges, where the tile itself is cut at 45 degrees, look best and are the hardest to do well.
Measure the exposed edges in linear feet before you order, because bullnose is often a separate item with its own lead time. Running out of it halfway is a two week delay.
Peel-and-stick, and when it makes sense
Peel-and-stick backsplash panels are sold by the sheet in a similar range of looks, and the square footage arithmetic here works for them unchanged — measure the run, multiply by the height, add waste, divide by the sheet size.
Two differences matter. Waste is lower, around 10%, because the sheets cut with scissors or a utility knife and cut-offs are more usable. And they need a genuinely smooth, clean, dry wall — any texture telegraphs through, and grease on a kitchen wall stops the adhesive working. Degrease and sand before you start.
They are a reasonable choice in a rental or a kitchen you plan to redo properly later. They are not a substitute for tile behind a range with a gas burner, where the heat will lift them.
How this is worked out
No black box — here is the arithmetic the calculator runs, so you can check it against your own numbers.
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main area = counter run × height ÷ 12Linear feet times inches gives square feet when divided by 12. -
− taller section width × standard height ÷ 12Removes the strip the range wall replaces, so nothing is double counted. -
+ taller section width × its height ÷ 12Adds the range wall back at its real height. -
× (1 + waste ÷ 100)15% standard; 20% for diagonal or herringbone. -
pieces = area ÷ area per tile, rounded upA 3 × 6 in. subway tile is 18 sq in. ÷ 144 = 0.125 sq ft. -
mastic = area ÷ 40One gallon covers about 40 sq ft with a 3/16 in. V-notch trowel. -
grout = area ÷ 50A 10 lb bag does roughly 50 sq ft of subway tile at 1/16 in. joints.
Common questions
How many square feet is a typical kitchen backsplash?
Most kitchens land between 16 and 30 square feet. A 12 ft run at the standard 18 in. height is 18 sq ft, and a taller section behind the range usually adds three to five more.
How high should a backsplash be?
Eighteen inches is the standard gap between a countertop and the upper cabinets, and tiling the full gap is the usual choice. Behind a range it commonly goes to 30 in. or all the way to the hood. A 4 in. strip is the old builder-grade minimum and looks dated now.
Do I subtract the outlets and the window?
Not the outlets — each one means a cut tile and a wasted cut-off, so the deduction and the waste cancel out. A window over the sink is worth deducting if it is over about 20 inches wide; just shorten the counter run you enter by the window width.
How many subway tiles are in a square foot?
Eight. A 3 × 6 in. tile is 18 square inches, and 144 divided by 18 is 8. So an 18 sq ft backsplash needs 144 tiles before waste, and about 166 with a 15% allowance.
Mastic or thinset for a backsplash?
Mastic for a normal dry kitchen wall — it is premixed and it grips vertical tile without sliding. Thinset for glass, natural stone, large-format tile, or anywhere behind a sink that may get properly wet. Check the tile maker's instructions; many specify one or the other.
How much grout do I need for a backsplash?
Usually one 10 lb bag, which covers around 50 sq ft of subway tile at 1/16 in. joints. Mosaic sheets have far more joint length and can use nearly double, so buy two bags if you are running mosaic.
Can I tile over an existing backsplash?
Sometimes, but it is rarely the right call. The new tile pushes everything forward — outlets, the gap under the cabinets, the counter edge — and any failure in the old tile takes the new one with it. Removing the old tile and skim-coating the drywall is a day's work and gives a much better result.
What do I do about the outlets sticking out?
Buy box extenders. Tile plus adhesive pushes the wall surface forward by about half an inch, and the outlet has to come with it or the cover plate will not sit flat. Extenders cost very little and fitting them after the tile is set is miserable.
Where these figures come from
Every figure below is traceable. How we check the numbers explains how they are verified, and the coverage reference collects them all in one place.
- Tile Council of North America handbook — adhesive selection and grout joint width guidance
- ANSI A108 / A118 — the standards mastic and thinset are rated against
- Manufacturer coverage charts — mastic spread rate by trowel notch and grout coverage by joint width
Think a number here is wrong? Tell us — we check every report, correct the page, and date the change. Last checked September 12, 2026.