Tile Calculator

How to Calculate How Many Tiles You Need

Start with the room's floor area — length times width, in square feet. Then find how much area a single tile covers, converting the tile's dimensions from inches to feet first. Dividing room area by tile coverage gives the raw number of tiles needed for a perfect, cut-free layout — which never happens in practice, so a waste percentage is added on top to cover trim cuts around edges, fixtures, and breakage.

$$\text{Tiles} = \left\lceil \frac{L \times W}{(t_w \div 12) \times (t_h \div 12)} \times \left(1 + \frac{\text{waste}}{100}\right) \right\rceil$$

Worked Example

A 12 ft × 10 ft room is 120 square feet. A 12-in × 12-in tile covers exactly 1 square foot (12 ÷ 12 = 1, squared). Without waste, that's 120 tiles. Adding the standard 10% waste allowance: 120 × 1.10 = 132 tiles. Note the room area used for ordering (132 sqft equivalent) is always somewhat more than the room's actual floor area — that gap is exactly the waste allowance, set aside for cuts around the room's edges and any fixtures like a toilet flange or cabinet toe-kick.

Metric Version of the Formula

Outside the US, room dimensions are measured in meters and tile dimensions in centimeters — switch the US/Metric dropdown above to convert both currently entered sub-scales at once. The tile count itself needs no conversion, since it's a plain count regardless of unit system.

$$\text{Tiles} = \left\lceil \frac{L \times W}{(t_w \div 100) \times (t_h \div 100)} \times \left(1 + \frac{\text{waste}}{100}\right) \right\rceil$$

A 4 m × 3.5 m room (14 m²) tiled with common 30 cm × 30 cm tiles (0.09 m² each, 900 cm²): without waste, 14 ÷ 0.09 ≈ 156 tiles. With 10% waste, 156 × 1.10 ≈ 172 tiles.

Choosing a Waste Percentage

10% covers a simple rectangular room laid in a straight grid pattern with minimal obstructions. A diagonal (45-degree) layout, a herringbone or basketweave pattern, or a room with lots of corners, alcoves, or fixtures commonly needs 15-20% instead — every one of those situations means more partial-tile cuts, and every cut piece wastes the unused remainder. Large-format tile also tends to waste more per cut in absolute terms than small tile, since a single mis-cut piece throws away a bigger chunk of material.

Common Tile Calculation Mistakes

Forgetting to convert tile dimensions from inches to feet before dividing is the most common error — it silently makes the coverage-per-tile number 144 times too large or too small depending on which way the mistake goes. Ordering with no waste allowance at all is the second most common, and the most expensive to fix mid-project: running short means placing a second order that may not perfectly match the first batch's dye lot, leaving a visible color mismatch. Measuring only the room's largest rectangle and forgetting an alcove, closet, or bump-out is the third — break an irregular room into rectangular sections and add them together rather than eyeballing one overall length and width.

Tile Terms You Should Know

Dye Lot — a manufacturing batch of tile; color and shading can vary slightly between lots, so buying enough in one order (including waste) avoids a visible mismatch later.

Grout Line — the gap between tiles filled with grout; wider grout lines slightly reduce the number of tiles needed to cover a given area, though most calculators (this one included) ignore that small effect.

Bullnose — a tile with one rounded, finished edge, used to cap an exposed edge (a shower curb, a step) where the raw tile edge would otherwise show.

Layout Pattern — how tiles are arranged (straight grid, diagonal, herringbone, brick/running bond); more complex patterns generally require a higher waste allowance.