Tile calculator

How to measure it on site

Tile is bought by the box and cut on site, so the measurement has two jobs: find the true square footage, and decide how much cutting waste the layout will produce. Measure the room and open one box before you order.

1. 01

   Measure the room at its widest points. Walls are rarely square. Measure length and width at both ends and use the larger figures, or split an L-shaped room into rectangles and add them.

2. 02

   Choose the waste factor by layout. A straight grid layout needs about 10 percent for edge cuts and breakage. A diagonal or herringbone pattern needs about 15 percent, because every edge cut wastes more of the tile.

3. 03

   Confirm the actual tile size. A nominal 12 × 12 tile often measures slightly under 12 inches so grout joints fit. Check the box or measure a tile; actual dimensions change the tiles-per-square-foot figure.

4. 04

   Read the box coverage, not the tile count. Boxes are labeled in square feet, and the count per box varies by tile size. Divide the area with waste by the box coverage, then round up — you cannot buy a partial box.

Common mistakes

Tile orders go wrong in predictable ways. Five of them account for most of the second trip to the store.

• Using a single waste factor for every layout. Ten percent is enough for a straight grid; diagonal and herringbone layouts need about 15 percent. A 100 sq ft floor is 110 sq ft straight but 115 sq ft on the diagonal, which can be a whole extra box.
• Counting tiles instead of boxes. A 10 sq ft box of 12 × 12 tile holds 10 tiles, but larger tiles come fewer per box. Always convert to boxes and round up; loose tiles are not sold as a top-up.
• Mixing dye lots. Tile color shifts slightly between production runs. Buy the entire job from one lot, and keep a spare box from that lot for future repairs — a later batch may not match.
• Trusting the nominal size. A tile sold as 12 × 12 may be 11.8 inches square. The difference is small per tile but changes the count across a whole floor, and it changes the grout joint width you can use.
• Underestimating grout. Standard 12 × 12 tile takes roughly 8 lb of grout per 100 sq ft; smaller tiles with more joints take up to about 12 lb. Buy a full bag rather than guessing from the tile count.

Worked example

What this calculator doesn't cover

This calculator sizes tile and grout from room dimensions. It does not cover these cases:

• —Pattern layout and cut plans — the calculator does not place tiles, plan the first course, or optimize where the cut edges land.
• —Subfloor and substrate preparation — deflection, backer board, and waterproofing are separate scope and decide whether the tile stays put.
• —Large-format and mosaic rates — very large tiles and small mosaics use different thinset and grout quantities than the standard rule.
• —Natural stone — stone varies in thickness and needs sealing and a different installation sequence.

Reviewed November 2026. Sources: Grout coverage and installation guidance (Tile Council of North America); Tile dimension and unit reference (ASTM International). Full methodology.

How the math works

Frequently asked questions

How much extra tile should I buy for waste and cuts?

Standard straight-lay tile installations require a 10% overage factor for cuts, edge trim, and accidental breakage. For diagonal installations, herringbone patterns, or rooms with lots of corners and obstacles, plan on 15% to 20% waste.

How do I calculate how many boxes of tile I need?

Multiply your room length by width to get total square footage, multiply by 1.10 (for 10% waste), and divide by the square footage printed on your specific tile box (typically 10 to 15 sq ft per box). Always round UP to the nearest whole box so you don't run short or mix dye lots later.

How many tiles are in a square foot?

For standard 12" × 12" tiles, exactly 1 tile equals 1 square foot. For 12" × 24" tiles, each tile covers 2 square feet (so 0.5 tiles per sq ft). For 6" × 24" plank tiles, each tile covers 1 square foot. For 4" × 12" subway tiles, you need 3 tiles per square foot.

How much grout do I need?

For standard 12" × 12" floor tiles with a standard 1/8" grout joint, plan on approximately 8 to 10 lbs of dry grout powder per 100 square feet. Smaller tiles like mosaic or subway tile have significantly more joints and can require 12 to 15 lbs per 100 sq ft.