Tile Calculator

Enter the size of one tile, the area to cover and the width of the grout joints. The calculator adds the gap to each tile's length and width, divides the area by that footprint and rounds up. With 12 × 12-inch tiles, ¼-inch joints and a 20 × 15 ft floor (300 square feet), each tile and its share of grout covers 12.25 × 12.25 inches, so the floor takes 288 tiles. Add a box size to see how many boxes to buy, and a price to estimate cost.

Always buy extra. Tiles along walls and around doorways, cabinets and pipes have to be cut, and some break. About 10% extra is the usual allowance for a straight layout in a simple room, 15% or more for diagonal or herringbone patterns, large-format tiles and rooms with many corners. Keep a few spare tiles from the same lot: dye lots vary, and a matching replacement can be impossible to find years later.

Gap Size

The gap is the grout joint between tiles. Joints absorb small differences in tile size, allow for slight movement and give the floor or wall its finished pattern. Narrow joints, about 1/16 to 1/8 inch, suit rectified tiles, which are machined to precise dimensions, and many wall tiles. Most floor tiles use 1/8 to 1/4 inch, while handmade, rustic or irregular tiles such as saltillo may need 3/8 inch or more. Tile manufacturers usually recommend a minimum joint width for each product, and industry standards discourage joints narrower than the tile's size variation allows.

Joint width also decides which grout to use: unsanded grout for joints under about 1/8 inch and sanded grout for wider joints, since the sand keeps the grout from shrinking and cracking. Plastic spacers set between the tiles keep the joints even during installation. For overlapping materials, such as some roofing or wall shingles, enter a negative gap.

Tile Installation Options

The layout pattern affects both appearance and how much tile you need. Straight lay, with joints in a simple grid, is the easiest and wastes the least. Offset or running-bond patterns, common with rectangular plank tiles, stagger each row; with long planks, many manufacturers recommend an offset of no more than a third of the tile length to avoid problems with any slight bow in the tiles. Diagonal layouts at 45 degrees make a small room look larger but need many triangular cuts along the walls. Herringbone and chevron patterns are striking but the slowest to lay and produce the most waste.

Good preparation matters more than pattern. Floors need a flat, stiff, clean substrate; cement backer board or an uncoupling membrane over a suitable subfloor is common, and wet areas such as showers need a waterproofing layer. Dry-lay a row of tiles first to plan the layout so that cut pieces at the edges are not too narrow, and start from the center of the room or the most visible wall.

Frequently asked questions