Tile Calculator

How to estimate tile

Tile is one of the few materials where the arithmetic is trivial and the judgment is everything. Area divided by tile size gives you a number in about two seconds. Deciding how much more than that to buy is the actual question.

tiles = area (sq ft) ÷ [tile width (in) × tile length (in) ÷ 144]
tiles to buy = tiles × (1 + waste)
boxes = tiles to buy ÷ tiles per boxDividing by 144 converts the tile's square inches into square feet. The waste factor is an estimating convention, not a manufacturer figure.

Tile area first

A 12 by 24 inch tile is 288 square inches, which is 2 square feet. An 80 square foot floor therefore needs 40 tiles before any allowance. A 6 by 6 tile is 36 square inches, a quarter of a square foot, so the same floor takes 320 of them.

Measure the room, not the tile box's marketing. Nominal sizes and actual sizes can differ slightly, and on a large floor a sixteenth of an inch per tile adds up across a run.

The waste factor is the real decision

Ten percent is the default for a straight lay in a simple rectangular room. That covers the cuts at the perimeter, the occasional tile that breaks, and a few spares.

Fifteen percent for a diagonal or offset layout. Running tiles at 45 degrees means every perimeter tile is a cut, and the triangular offcuts are rarely reusable elsewhere.

Twenty percent for herringbone, chevron, or a room full of jogs, alcoves, and things to cut around. Every direction change costs material.

These are trade conventions rather than published specs, and this page will not pretend otherwise. What makes them defensible is that they describe a physical reality: the more cuts your layout forces, the more of each cut tile ends up in the bin.

Large tiles waste more

Worth thinking about before you commit to a format. When you cut a 6 inch tile to fill a 3 inch gap, you lose 3 inches of tile. When you cut a 24 inch tile to fill the same gap, you lose 21 inches.

Large-format tile in a small or irregular bathroom is exactly the situation where a flat 10 percent is most likely to leave you short. If you are running big tiles in a room with a lot of perimeter relative to its area, take the next waste factor up.

Why the answer is in boxes

Because that is the unit stores actually sell. Knowing you need 43 tiles does not help at the counter if they come 8 to a box, and the box count always rounds up.

That rounding usually leaves you with more spares than the waste factor alone would suggest, which is a feature rather than a bug. Which brings us to the part most calculators skip.

Keep the leftovers, and buy the lot together

Tile is manufactured in production runs, and color varies between them. Two boxes of nominally identical tile bought a year apart can be visibly different side by side. Tile lines also get discontinued regularly.

So two rules. Buy every box in one purchase and check they carry the same lot or batch number printed on the box. And keep the spares somewhere dry rather than returning them, because a cracked tile three years from now can only be matched from the original lot.

This is the strongest argument for erring toward the higher waste factor rather than the lower one. The marginal box is cheap now and impossible later.

A quick cost check

An 80 square foot floor in 12 by 24 tile is 40 tiles bare. At 10 percent that is 44, and at 8 to a box, 6 boxes or 48 tiles. At 15 percent it is 46 tiles, still 6 boxes. At 20 percent it is 48 tiles, exactly 6 boxes.

Notice all three land on the same purchase. Box rounding often swallows the difference between waste factors entirely, which means choosing the higher one frequently costs nothing at all. Check before you agonize.

Common estimating mistakes

• Forgetting to divide by 144. Tile is sold in inches and rooms are measured in feet.
• Using 10 percent on a diagonal layout. The pattern determines the waste, not the room.
• Buying boxes separately. Different lots, visible color difference, no way back.
• Returning the spares. The refund is small and the replacement tile is unobtainable.
• Estimating thinset from area alone. It depends on the trowel notch, which depends on the tile size. Read the bag.

When to call a pro

Not for the tiling itself, which is learnable. For what is underneath it.

Tile is rigid and unforgiving, and it fails when the substrate moves or stays wet. A bouncy floor will crack grout and then tile, and the fix is structural rather than cosmetic. Shower and wet-area waterproofing is the other one: a shower that leaks behind the tile causes damage you will not see until it is expensive. Both of those are worth getting right before a single tile goes down.