8x10 room, 18in tile

Tile quantity comes down to two areas divided into each other: the total floor area of the room, and the area of a single tile. Room area is simply length times width. Tile area starts from the tile's side length in inches, which this calculator converts to feet by dividing by 12, then squares to get the area of one square tile in square feet. Dividing room area by tile area gives the raw number of tiles needed to cover the floor with no waste at all.

Waste factor matters more for tile than for almost any other material, because a tile installation is full of cuts — full tiles rarely line up perfectly against every wall, doorway, or fixture, and once a tile is cut the leftover offcut is usually too small to reuse anywhere else in the room. The standard trade recommendation is about 10% extra for a simple square (grid) layout in a rectangular room, but that should climb to 15-20% for a diagonal or herringbone layout, a room with lots of jogs and corners, or when using large-format tile where a single miscut wastes a lot of material.

Tile size itself changes the waste-and-labor tradeoff. Larger format tiles, like 24-inch squares, mean fewer total tiles and fewer grout lines, but each cut wastes more material and the tile is less forgiving of an uneven subfloor, since a single high or low spot under a big tile is more visible than under a small one. Smaller tiles, like 6-inch squares, need far more pieces and more cutting operations overall, but each individual miscut costs much less material and the tile can flex slightly to accommodate small subfloor imperfections.

This calculator assumes a simple rectangular room and square tiles. Real rooms are often L-shaped or have alcoves, closets, or bump-outs — the standard approach is to split the space into two or more rectangular sections, run each one through this calculator separately, and add the tile counts together. Rectangular (non-square) tiles, like common 12x24 planks, need their own length-times-width area calculation rather than squaring a single side length.

In practice, tile is sold by the box, and each box covers a fixed square footage printed on the label — not by the individual tile. Once you have the tile count from this calculator, check the box coverage for the specific tile you're buying and round up to whole boxes, since a partial box still has to be purchased in full and having a couple of spare tiles on hand is useful for future repairs.