Tile Calculator – How Many Tiles and Boxes to Buy
This tile calculator works out how many tiles you need for a floor, wall or backsplash, and how many boxes that means at the store. It takes into account the grout joint and a waste allowance that suits your laying pattern. It also draws the actual layout at scale, with the cut tiles shaded, so you can see where the slivers will fall before you buy a single tile.
Measuring Floors and Walls
Measure wall to wall at floor level and enter each area as a rectangle, triangle, circle or known area. An L-shaped room is simply two rectangles. For a wall or backsplash, enter the length times the tiled height. Anything that sits where no tile goes, such as a bath, kitchen island or fitted cabinets, can be added as a Subtract area. The net area is everything added minus everything subtracted.
Nominal vs Actual Tile Size
Tile names are nominal. A "12 × 12" tile often really measures about 11.8 in (300 mm), and a "24 × 24" might be 23.6 in. On a large floor that difference adds up, so enter the actual size from the box label or a tape measure. The calculator then divides the net area by the tile's cell, which is the tile plus its share of grout: (w + g) × (l + g) for rectangles. For a hexagon it uses √3 ÷ 2 × (F + g)², where F is the flat-to-flat size.
Choosing a Waste Percentage
Every row and column that meets a wall ends in a cut tile, and some tiles break. Typical allowances are 10% for straight and offset layouts, 15% for diagonal and hexagon tile, and 20% for herringbone, where both ends of many planks are cut. Small rooms, lots of corners and fragile or large-format tile push the figure up. For a straight grid in a simple rectangular room, the calculator also counts the actual tile positions and warns you if your estimate would leave you short.
Patterns and Lippage
A running-bond (brick) pattern with a ½ offset looks classic, but long tiles are rarely perfectly flat. Offsetting them by half puts the high middle of one tile next to the low ends of its neighbours, which creates lippage, a ridge you can feel underfoot. Industry guidance (ANSI A108.02 / TCNA, as commonly cited) recommends an offset of no more than ⅓ for tiles longer than 18 in (457 mm). Herringbone needs planks at least twice as long as they are wide.
Avoiding Slivers by Centring
If you start at one wall, the last tile at the opposite wall is whatever is left over, and that can be a thin sliver that is hard to cut and looks wrong. Centring the layout splits the leftover into two equal cuts, one at each wall. For example, a 122½ in side with 12 in tiles leaves a 1¼ in sliver from the wall, but centred it gives two 6⅝ in cuts. The layout check shows both options.
Grout and Thinset
Grout depends on the joint width, the joint depth (usually the tile thickness) and the amount of joint per square foot, which is much higher for small tiles. The calculator uses the manufacturer formula (A + B) ÷ (A × B) × joint × depth × density and adds 10%. Thinset (tile adhesive) coverage depends on the trowel notch, and larger tiles need a larger notch. The coverage chart printed on your bag is the best guide.
Keep Spare Tiles From the Same Batch
Tiles are made in batches, or lots, that can differ slightly in shade and size. Make sure every box shows the same lot number, and keep a few unopened spares. If a tile cracks years later, you will have a perfect match. Trim pieces such as bullnose, edge trim and stair nosing are sold by length, not area, so count those separately.