How to Calculate How Many Tiles You Need for a Room

To calculate how many tiles you need, divide the floor area by the area of one tile, then add 10% for waste: a 100 square foot floor with 12 by 12 inch tiles needs 100 tiles plus 10 spare, or 110 tiles. Get the count with our free Tile Calculator, and read on for the grout-joint adjustment and waste rates.

Try it now: Tile Calculator →

Measure the Floor and the Tile

Measuring the floor correctly is the first step, and it matters more than the arithmetic, because every later number inherits a measuring error. Measure the length and width of the room in feet at floor level, wall to wall, and multiply them for the area: a room 10 feet by 12 feet is 120 square feet. For L-shaped rooms, split the floor into rectangles on paper, measure each rectangle, and add the areas, because a single length-times-width figure for an irregular room is always wrong. Subtract nothing for small fixtures: a toilet or vanity footprint is small, and the tiles cut around it come from the waste allowance, not from a deduction. Next, find the area of one tile: a 12 by 12 inch tile covers 1 square foot, a 6 by 6 inch tile covers 0.25 square feet, and a 24 by 24 inch tile covers 4 square feet, because tile area in square feet is length in inches times width in inches divided by 144. The tile count before waste is floor area divided by tile area, so the 120-square-foot room needs 120 twelve-inch tiles, 480 six-inch tiles, or 30 twenty-four-inch tiles. For the metric side of the same measurement, our square feet to square meters converter translates the floor area, and the square meters to square feet converter runs it back when a tile box is labeled in metric.

The Grout Joint Changes the Count

The grout joint changes the tile count by a small but real amount, and most thin calculators ignore it, which is why their counts run short. A tile plus its grout joint occupies more area than the tile alone: a 12-inch tile with a 1/8-inch joint on each side effectively covers 12.125 inches per side, so its effective area is about 1.02 square feet instead of 1.00, and a 120-square-foot floor needs about 118 tiles instead of 120, which is a small saving, not a cost. The effect reverses for small tiles: a 2-inch mosaic tile with a 1/8-inch joint effectively covers 2.125 inches per side, which is 6 percent more area per tile, so the count drops by about 6 percent, and ignoring the joint over-orders by that margin. The practical rule is to compute the count with the joint included when the tile is small or the joint is wide, and to treat the joint as negligible for large-format tiles with narrow joints, because the difference there is under 2 percent and sits inside the waste allowance anyway. Joint width also affects grout quantity: wider joints need more grout per square foot, and a floor with 1/4-inch joints uses roughly twice the grout of the same floor with 1/8-inch joints, which is a separate purchase to size from the joint, not from the tile count. Our 20 by 20 room guide shows the same area-first method on a larger floor, and its flooring section covers the box math that follows here.

Waste by Layout: Straight, Diagonal, and Herringbone

Waste by layout is where tile orders most often go wrong, because the layout decides how many tiles get cut and how many cuts are unusable. A straight layout, where tiles run parallel to the walls, wastes about 10 percent: cuts happen only at the walls, and most offcuts are too small to reuse. A diagonal layout, where tiles run at 45 degrees to the walls, wastes about 15 percent, because every wall edge produces triangular offcuts that cannot be reused elsewhere. A herringbone layout wastes about 20 percent, because the zigzag pattern produces angled cuts at every edge and the pattern itself consumes extra tiles at the borders. Brick or running-bond layouts sit near the straight rate at about 10 percent, while basketweave and complex patterns should be budgeted at 15 to 20 percent depending on the room shape. Room shape multiplies the layout effect: a square room wastes less than an L-shaped room with the same area, because more edges mean more cuts, and a room with many corners, niches, or angled walls should add 5 percent to whichever layout rate applies. The formula with waste is tiles to buy equals tiles needed times one plus the waste rate, so 120 tiles at 10 percent is 132 tiles, at 15 percent is 138 tiles, and at 20 percent is 144 tiles, and rounding up to whole boxes happens after the waste, never before, because rounding twice inflates the order.

Boxes, Spares, and the Final Order Check

Boxes, spares, and the final order check turn a tile count into a purchase that survives the job. Tiles are sold by the box, and boxes are labeled with their coverage in square feet, so divide the total area to buy by the box coverage and round up: 132 tiles at 1 square foot each is 132 square feet, and at 10 square feet per box that is 13.2 boxes, rounded up to 14 boxes. Always buy one extra box beyond the rounded figure for future repairs, because dye lots change between production runs, and a tile bought six months later can differ visibly in shade even with the same product code. The spare box is cheap insurance against a cracked tile, a plumbing repair, or a future extension, and it costs far less than retiling a floor because one tile cannot be matched. The final order check has four items: the floor area was measured twice, the tile size and joint width match the box label, the waste rate matches the layout, and the box count was rounded up after waste, not before. If any item fails, remeasure before ordering, because returning opened tile boxes is difficult and reordering risks a shade mismatch. For the full calculation with grout joints, layout waste, boxes, and cost in one place, our Tile Calculator runs all four checks automatically, and the room-area math behind it is the same method as our square feet to square meters formula guide.