Tile Calculator – How Many Tiles Do I Need?

Enter your room dimensions and tile size and I’ll tell you how many tiles to buy, including enough extra for cuts and breakage so you don’t come up short mid-job.

How I calculate this

The formula is straightforward: divide your room’s square footage by the area of one tile, then add a waste allowance. The waste part is where I see people get burned, so I want to be clear about the numbers I use.

First, I find your room area in square feet (length x width). If you enter the dimensions separately, I multiply them; if you already know the square footage, I use it directly.

Next, I figure out the area of one tile in square feet. A 12×12-inch tile is exactly 1 sq ft. An 18×18-inch tile is 2.25 sq ft (18 x 18 = 324 square inches, divided by 144 = 2.25 sq ft). A 12×24-inch tile is 2 sq ft. A 24×24-inch tile is 4 sq ft. If you enter a custom size, I do the same conversion: multiply the two dimensions in inches and divide by 144.

I divide the room area by the tile area to get the raw tile count, then add waste:

• Straight lay (tiles set in a standard grid): 10% waste. This is the industry standard for simple rectangular rooms with a straightforward grid pattern.
• Diagonal or herringbone lay: 15% waste. Angled cuts at every wall produce a lot of unusable triangular pieces. For complex patterns (chevron, mosaic with lots of cuts), I’d push this to 20%, which you can do by selecting “Complex pattern” from the pattern dropdown.

After adding waste I round up to whole tiles, because you can’t buy a fraction of a tile. If you enter a box coverage (how many square feet your chosen tile’s box covers), I divide the total into boxes and round up there too.

Grout joint width affects coverage slightly, but for planning purposes a 1/8-inch joint on a 12×12 tile adds less than 2% to area, so I don’t inflate the formula for it. The waste factor already covers the real-world shortfall.

Source for waste percentages: Inch Calculator tile guide; industry guidance confirmed by Bob Vila.

A worked example

Say you’re tiling a kitchen floor that’s 10 feet by 12 feet, using 12×24-inch tiles in a straight lay.

Room area: 10 x 12 = 120 sq ft. One 12×24 tile: 12 x 24 = 288 square inches, divided by 144 = 2 sq ft per tile. Raw tile count: 120 / 2 = 60 tiles. Add 10% waste: 60 x 1.10 = 66 tiles. Round up: 66 tiles.

If your tile comes in boxes that cover 16 sq ft each, you need 120 sq ft (with waste, call it 132 sq ft) divided by 16 = 8.25 boxes. Round up to 9 boxes.

That 9th box is not overkill. I’ve done enough tile jobs to know that one box of the same dye lot sitting in the garage is worth every dollar, either for repairs down the road or because the last row didn’t go as cleanly as expected.

Tips before you buy

The dye lot matters more than most people realize. Tiles from different production runs can vary slightly in shade, and you won’t notice until they’re side by side on the floor under bright light. Order everything you need from one lot. The lot number is printed on the box. If you have to order more later and the lot is gone, you may be stuck.

For diagonal lay, add 15% minimum and don’t argue with it. Diagonal cuts at both ends of every row eat material fast. On a small bathroom floor I once thought 10% would cover it at 45 degrees. It didn’t. I made two hardware store runs.

If the room has an L-shape, alcoves, or a lot of obstacles (toilet flanges, door casings, a freestanding tub), I’d add another 5% on top of whatever the pattern calls for. The calculator gives you a clean-room number; irregular rooms burn more.

Measure twice. Tile is not forgiving of math errors, and the return policy on cut tile is typically zero. If you’re unsure how to get an accurate room measurement, see how to measure a room before you fill in the calculator.

Tile size also affects perceived room size. Large-format tiles (24×24 or bigger) make a small room feel more open because fewer grout lines interrupt your eye. In a bathroom under 50 sq ft, a 12×12 can look busier than you expect. This doesn’t change the math, but it’s worth knowing before you commit.

For more on patterns and spacing, see the tile spacing and layout guide.

FAQ

How much extra tile should I buy? For a straight grid layout in a square or rectangular room, 10% overage is standard. For diagonal, herringbone, or any 45-degree pattern, use 15%. For irregular rooms or complex patterns like chevron, go to 20%. Always round up to full boxes, not individual tiles.

Does grout joint width change how many tiles I need? Slightly, but not enough to change your tile count in most cases. A 1/8-inch grout joint on 12×12 tiles adds roughly 1-2% to your effective coverage area, which the waste factor already absorbs. If you’re using wide grout joints (3/8 inch or more) with very small tiles, it’s worth noting, but for standard 12×12 and up the formula here is accurate for planning.

What are the most common tile sizes? The most popular floor tile sizes are 12×12, 12×24, 18×18, and 24×24 inches. Large-format tiles (24×24 and bigger) are increasingly common for open-plan floors. Smaller tiles (4×4, 6×6) show up on bathroom walls and backsplashes. The calculator handles any size you enter.

What if I don’t know the box coverage? Leave the box field blank and the calculator gives you the total tile count. Then check the box at the store: it will state the coverage in square feet per box. You can do the division in your head: total tiles divided by tiles per box, rounded up.

Can I use this for wall tile too? Yes. The math is identical: room area (wall height x width) divided by tile area, plus waste. For a shower surround with many obstacles (valve, niche, shampoo shelf), I’d use 20% rather than 10%, because the cuts are relentless.

Built and maintained by Sam Walsh. Last updated July 2026. Tile counts are planning estimates based on standard waste factors; actual usage depends on your room shape, layout, and installer technique.

Not sure how to get your room dimensions right? Read how to measure a room first. Laying hardwood or vinyl in the same space? The flooring calculator uses the same area math. Also painting? Try the paint calculator.