Backsplash Calculator

Calculate how many tiles you need for a kitchen backsplash from the counter length and height, plus the square footage to buy, boxes, tile adhesive and cost.

By CalcBuilt Editorial TeamUpdated September 9, 2026Formulas checked against manufacturer specs, see how we calculate.

Quick answer: To find how much backsplash tile you need, multiply the counter length by the backsplash height for the area, divide by the size of one tile plus its grout joint, then add 10% for cuts. A 15 ft counter with an 18 in backsplash is 22.5 sq ft, which takes 175 subway tiles of 3 x 6 in with a 1/16 in joint, or 192 tiles with waste.

Results

Tiles to buy: 192 tiles; 175 tiles of 3 x 6 in plus 10% waste
Area to buy: 24.8 sq ft; 22.5 sq ft of wall plus 10% waste
Tile adhesive (mastic): 0.5 gal; At about 45 sq ft per gallon with a 3/16 in V-notch trowel

Backsplash formula

Area (sq ft) = Counter length (ft) x Backsplash height (in) / 12 + extra area
Tile footprint (sq in) = (Tile width + grout gap) x (Tile length + grout gap)
Tiles = Area x 144 / Tile footprint x (1 + waste %), rounded up
Mastic (gal) = Area / 45

Worked example

A 12 ft counter with an 18 in backsplash and 6 sq ft of extra tile up to the range hood, using 4 x 12 in tile with a 1/8 in joint: 12 x 18 / 12 = 18 sq ft, plus 6 = 24 sq ft, or 3,456 sq in. Each tile occupies 4.125 x 12.125 = 50.02 sq in. 3,456 / 50.02 = 69.1 tiles. Add 10% waste: 69.1 x 1.1 = 76.01, so buy 77 tiles, or 2 boxes of 40.

Buy 24 x 1.1 = 26.4 sq ft of tile. Mastic: 24 / 45 = 0.53 gallons, so one 1 gallon tub. At $8 per sq ft the tile costs 26.4 x 8 = $211.

Quick reference

Subway tile (3 x 6 in, 1/16 in joint) for an 18 in backsplash
Counter length	Area	Tiles	Tiles with 10% waste
8 ft	12 sq ft	94	103
10 ft	15 sq ft	117	128
12 ft	18 sq ft	140	154
15 ft	22.5 sq ft	175	192
20 ft	30 sq ft	233	256
25 ft	37.5 sq ft	291	320

How to measure a backsplash

Measure the length of every wall section that will get tile, including short returns beside a window or refrigerator, and add them up. Multiply by the height from the counter to the bottom of the upper cabinets, normally 18 in, to get the area in square feet. If the tile runs up to the range hood or continues on a wall with no cabinets, measure that rectangle separately and add it as extra area.

Do not subtract outlets and switches; the cuts around them are where most of the waste goes. A 10% allowance is enough for a straight running bond with a handful of outlets. Go to 15% for herringbone, diagonal or a wall with a window in the middle of the tile field, and keep a few spare tiles from the same dye lot for future repairs.

Adhesive, layout and finishing

Premixed tile mastic is the easiest adhesive for a dry backsplash: spread it with a 3/16 in V-notch trowel and it covers about 45 sq ft per gallon. Behind a range or around a window many installers switch to thinset mortar, which handles heat and moisture better; a 50 lb bag with a 1/4 in square notch covers roughly 95 sq ft. Glass tile and natural stone also call for a white thinset so the adhesive does not show through.

Snap a level line on the wall, since counters are rarely level, and start from the most visible point, usually the center of the sink wall or the range, so cuts land in the corners. Leave a 1/8 in gap at the counter and fill it with color-matched caulk rather than grout. Outlets need box extenders so the receptacle sits flush with the new tile face.

Key facts

A 3 x 6 in subway tile covers 18 sq in, so there are 8 tiles per square foot before grout joints and waste.
The standard backsplash height is 18 in, the gap between a 36 in counter and upper cabinets hung at 54 in.
Tile mastic covers about 45 sq ft per gallon with a 3/16 in V-notch trowel, the usual choice for tile under 8 in.
Mosaic sheets are 12 x 12 in, so one sheet covers 1 sq ft; a 4 x 12 in tile takes 3 per square foot.
Add 10% waste for a running bond layout and 15% for herringbone, diagonal or a wall with several outlets.

Frequently asked questions

How many square feet is a typical backsplash?

Most kitchens have 20 to 40 sq ft of backsplash. A 15 ft counter run with an 18 in backsplash is 22.5 sq ft; add whatever runs up behind the range hood.

How many 3 x 6 subway tiles do I need for 30 square feet?

About 233 tiles with a 1/16 in grout joint, or 256 with 10% waste. Without joints it works out to exactly 8 tiles per square foot.

Should I use mastic or thinset for a backsplash?

Mastic is fine for ceramic and porcelain tile on a dry kitchen wall and spreads about 45 sq ft per gallon. Use thinset for glass, stone, large tile, or directly behind a range where heat and steam are constant.

How high should a backsplash be?

The standard is 18 in, the space between a 36 in high counter and upper cabinets at 54 in. Behind the range it usually continues up to the hood, about 30 in above the cooktop.

Sources and references

AcrylPro Professional Tile Adhesive product page (Custom Building Products)
AcrylPro Professional Tile Adhesive technical data sheet TDS-127 (Custom Building Products)
Type 1 ceramic tile mastic product page (MAPEI)

Next steps for this project

The usual order for a flooring & tile project. See all flooring & tile calculators.

Results are estimates based on standard formulas and typical product specifications. Confirm quantities with your supplier and local code before ordering.