Tile Calculator

How to measure the surface

For floors, measure the room’s length and width in feet at the widest points and multiply. A 5 × 8 ft bathroom floor is 40 sq ft. Split irregular rooms into rectangles and add them up, and remember to include the floor of a walk-in shower or a closet if it’s getting the same tile.

For walls, measure the width and height of each section you’re tiling and multiply, then add the sections together. A kitchen backsplash is typically the strip between the counter and the upper cabinets, about 18 inches tall, so measure its length in feet and multiply by 1.5. For a tub surround, measure each of the three walls separately from the tub deck up to your planned stopping height.

Subtract large openings like a window inside a shower wall, but don’t bother subtracting outlets or faucet penetrations. The cuts around them waste more tile than the holes save.

Last, note your tile’s size in inches off the box or the product page: 12 × 12, 12 × 24, 3 × 6 subway, and 24 × 48 are the common US formats.

The formula and what it assumes

Two steps. First the calculator converts your tile’s dimensions to square feet:

Tile area = (width in inches × length in inches) ÷ 144.

A 12 × 24 tile is 288 ÷ 144 = 2 sq ft. A 3 × 6 subway tile is 18 ÷ 144 = 0.125 sq ft.

Then it figures the count:

Tiles = surface area × (1 + waste %) ÷ tile area, rounded up to a whole tile.

For that 40 sq ft bathroom with 10% waste and 12 × 12 tile: 40 × 1.10 ÷ 1 = 44 tiles.

The default waste factor is 10%, which absorbs perimeter cuts, the occasional cracked tile, and a few keepers for future repairs. Use 15% for diagonal or herringbone layouts, since angled cuts produce unusable triangles at every edge, and for rooms with lots of jogs and corners.

One assumption worth spelling out: the formula ignores grout lines, and that’s intentional. At standard 1/8 to 3/16 inch spacing, grout joints reduce the tile count by only one or two tiles on a typical floor, far less than the waste allowance already covers. Treating grout as a buying-decision factor only makes sense with very wide joints on small tile, which is rare in residential work.

The formula also assumes a flat surface. Niches, benches, and curbs in a shower add area; measure each face and add it to your total.

Buying tips

Tile in the US sells by the box, and every box states its coverage in square feet, usually somewhere between 8 and 16 sq ft depending on tile size. Shopping by square footage is simpler than counting individual tiles: take your area-plus-waste number and divide by the box coverage, rounding up. Loose single tiles are sometimes available at tile specialty stores but rarely at big-box retailers.

Match the tile grade to the job. Porcelain is denser and less absorbent than ceramic, which matters in showers and entryways; for floors, check the PEI wear rating (PEI 3 or higher for residential floors) and pick a finish with some texture for wet areas, since polished tile is slick underfoot. Wall-rated tile is often thinner and softer and should never go on a floor, though floor tile can usually go on walls.

Buy everything in one order and check the dye lot and caliber codes printed on the boxes. Tile color and even exact size shift between production runs, and a mismatched box in the middle of a floor is obvious forever. If a store has to pull stock from two lots, ask them to keep looking.

Round up generously. Unopened boxes return without drama at the major retailers, generally within 90 days with a receipt, so the extra box costs you nothing but a trip. Before you return it, though, pull out four or five tiles and keep them. A cracked tile under a dropped pan is a ten-minute fix when the match is sitting in the garage, and a renovation when it isn’t.

Frequently asked questions

How much extra tile should I buy for waste?

10% extra covers a standard straight-lay job: edge cuts, breakage, and a few spares. Move to 15% for diagonal or herringbone layouts, rooms with many corners, or large-format tile where one bad cut wastes a lot of material.

Do grout lines change how many tiles I need?

Not meaningfully at standard spacing. A 1/8 to 3/16 inch grout joint shifts the count by only a tile or two on a typical floor, well inside the 10% waste allowance. Only very wide joints (1/2 inch or more) with small tile are worth recalculating for.

How many tiles come in a box?

It depends on tile size. Boxes of 12 × 12 inch tile often hold 10-15 tiles, while 12 × 24 inch tile commonly comes 6-8 per box. Every carton lists its square-foot coverage, which is the easier number to shop by.

Can I return leftover tile?

Unopened boxes generally return fine at Home Depot, Lowe's, and Floor & Decor with a receipt, usually within 90 days. Opened boxes and special orders often don't. Keep a handful of spare tiles anyway, since matching a discontinued tile years later is nearly impossible.