How Many Tiles Do I Need?

Order too few tiles and the job stalls; order too many and money sits in the garage. A short calculation gets it right. Here is how to work out the tiles for a floor or wall by hand, with a worked example and the traps to dodge.

The short version: find the area, work out how much one tile covers, divide to get the count, then add a waste factor and round up to whole boxes. The waste allowance is the part most people skip.

Find the area to cover

Tiles cover area, so start with the square footage. For a floor, multiply the length by the width in feet. A kitchen that is 12 feet by 9 feet is 12 × 9 = 108 square feet.

A wall works the same way: use its height and width in place of the floor’s length and width. If the room is an odd shape, split it into rectangles, find each area, and add them together.

Work out one tile’s coverage

Tiles are sized in inches, but the area is in feet, so convert. Multiply the tile’s width and height in inches, then divide by 144, since 144 square inches make one square foot.

For an 18 by 18 inch tile: 18 × 18 = 324 square inches, and 324 / 144 = 2.25 square feet per tile. Now both the area and the tile are in the same unit, ready to divide.

Divide, then add the waste factor

Divide the area by the tile coverage: 108 / 2.25 = 48 tiles to cover the floor exactly. But a clean count never survives contact with the room, so add a waste factor for cuts and breakages.

1. Bare count: 48 tiles.
2. Add 10 percent: 48 × 1.10 = 52.8.
3. Round up: 53 tiles.

Ten percent is the standard allowance for a straight grid. The edges need trimming to fit, tiles crack under the cutter, and you want a few spares from the same batch for repairs.

Round up to whole boxes

Tiles sell by the box, not the piece, so turn the tile count into boxes. Check the label for the tiles per box, then divide and round up. At 6 tiles per box, 53 / 6 = 8.8, which rounds to 9 boxes.

Buying whole boxes usually adds a few more spares on top of your waste allowance, which is fine. Those extras live in the closet as your future repair stock, matched to the exact shade you laid.

When to raise the waste factor

Ten percent fits a plain grid where tiles run parallel to the walls. A diagonal layout cuts every edge tile at an angle, which wastes more, so bump the allowance to 15 percent.

Herringbone and other angled patterns are hungrier still, since the repeating angle leaves many partial tiles around the perimeter. For those, plan on 15 to 20 percent so a tricky cut near the end does not send you back to the store.

Match the batch, or dye lot

Tiles are made in batches, and the color can shift slightly between them. That shift is called the dye lot, and it is why buying enough in one go matters more than with most materials.

Run short and a second order may arrive a shade off, visible across a finished floor. The waste factor and the round-up to whole boxes both guard against that, which is the real reason to over-order a little.

Common mistakes to avoid

• Skipping the unit conversion. Tile sizes are in inches, so divide by 144 before comparing to an area in square feet.
• Leaving out the waste factor. A bare count gives no room for cuts, breakages, or spares.
• Buying loose tiles instead of boxes. Round the count up to whole boxes, since that is how tiles are sold.
• Ordering in two trips. A later batch can be a different dye lot, so buy the full amount at once.

Frequently asked questions

How do I convert tile size to square feet? Multiply the tile’s width and height in inches, then divide by 144. An 18 by 18 inch tile covers 2.25 square feet.

What waste factor should I use? Ten percent for a straight grid. Raise it to 15 or 20 percent for diagonal or herringbone layouts, which produce more offcuts.

Why round up to whole boxes? Tiles are sold by the box, not the piece. Rounding up covers the count and leaves spares from the same batch for repairs.

What is a dye lot? The production batch a tile came from. Color can vary slightly between lots, so buy enough at once to avoid a visible mismatch.

Do I need to do this by hand? No. The method is useful to understand, but a tool is faster. Use the one below to enter the area and tile size and see the tiles and boxes in a second.