About the tile calculator
Most quick tile estimates divide the room area by the tile area and stop there. That ignores two things: the grout joint, which slightly reduces the number of tiles needed, and cutting waste, which increases it. This calculator includes both, and then rounds up to whole tiles and whole boxes.
Enter tile sizes in inches or millimetres. Fractions such as 1/8 or 3/16 are accepted for joint widths.
How to use it
- Measure the area to tile, or enter the total if you have split the room into sections.
- Enter the actual tile size (not the nominal size) and your joint width.
- Choose a waste allowance: around 10 % for straight layouts, more for diagonal or herringbone patterns, large-format tile or rooms with many corners.
- Enter tiles per box and price per box from the packaging to see box count and cost.
Formula
Effective tile area
a = (tile length + joint) × (tile width + joint)Tiles (exact)
n = area ÷ aTiles to buy
N = ⌈ n × (1 + waste % ÷ 100) ⌉Boxes
boxes = ⌈ N ÷ tiles per box ⌉- Each tile occupies its own area plus half a joint on every side, which is the same as adding one full joint width to each dimension.
Worked example: A 12 ft × 10 ft floor with 12 × 12 in tiles and 1/8 in joints
- Area = 120 ft² = 17,280 in²
- Effective tile = 12.125 × 12.125 = 147.0 in²
- 17,280 ÷ 147.0 = 117.5 tiles
- +10 % waste = 129.3 → 130 tiles
Result: Buy 130 tiles (for example 13 boxes of 10).
Assumptions and limitations
- The waste allowance covers cuts and breakage; patterned layouts and tiles with directional veining may need more.
- Buying all tiles from the same batch (shade/lot number) is strongly recommended, so it is safer to buy a little extra now than to top up later.
Frequently asked questions
How much extra tile should I buy?
About 10 % for a straight layout in a simple room, 15 % for diagonal layouts or many cuts, and up to 20 % for herringbone. Keep a few spare tiles for future repairs.
Do grout lines change how many tiles I need?
Slightly. With small tiles and wide joints the difference can be several percent; with large tiles and narrow joints it is small. The calculator includes it automatically.
Should I use nominal or actual tile size?
Use the actual size printed on the box. Nominal sizes are sometimes rounded.
How do I tile an L-shaped room?
Split it into rectangles, add the areas together and use the "I know the total area" option.
Sources and further reading
Results are estimates for planning purposes. See our disclaimer for details.