How to use the tile calculator
Enter the floor or wall area (as length × width, or the square footage directly), pick a tile size from the presets or type your own, choose the grout gap and waste allowance, and the calculator returns the number of tiles to buy. Add tiles-per-box to get whole boxes, and a price per square foot for the cost.
The maths
tile footprint (sq ft) = (tile width + gap) × (tile length + gap) ÷ 144
tiles needed = area ÷ footprint × (1 + waste %)Each tile “owns” half the grout line on every side, so the footprint uses tile size plus gap. Dimensions are in inches, area in square feet — the 144 converts square inches to square feet.
Tiles per square foot (quick reference, 1/8” grout)
| Tile size | Tiles per sq ft |
|---|---|
| 4 × 4 in | 8.5 |
| 3 × 6 in (subway) | 7.5 |
| 6 × 6 in | 3.8 |
| 8 × 8 in | 2.2 |
| 12 × 12 in | 1.0 |
| 12 × 24 in | 0.49 |
| 18 × 18 in | 0.44 |
| 24 × 24 in | 0.25 |
| 6 × 36 in (plank) | 0.65 |
Choosing the waste allowance
Waste comes from cutting tiles at walls and around obstacles, breakage in transit and installation, and mistakes. Guidelines:
- 5% — a small, simple rectangle, tiles laid parallel to the walls, experienced installer.
- 10% — the usual figure for most rooms.
- 15% — diagonal or herringbone layouts, which need angled cuts on every edge tile; rooms with alcoves, islands or many corners.
- 20%+ — large-format tile (where one broken piece is a lot of area), natural stone with variation you’ll want to select from, or a first-time DIY job.
Other materials for the job
- Thin-set mortar: roughly one 50 lb bag per 40–50 sq ft for 12-inch tile with a 1/4-inch notched trowel; larger tiles need a bigger trowel and more mortar.
- Grout: a 10 lb bag covers about 40–60 sq ft of 12-inch tile with 1/8-inch joints; narrow joints and large tiles use less.
- Backer board for floors and wet areas: sold in 3 × 5 ft sheets (15 sq ft each).
- Spacers, a levelling system for large tiles, and sealer for natural stone or cement-based grout.
Measure irregular rooms with the square footage calculator first, then bring the total here.
Frequently asked questions
How many 12×12 tiles do I need for 100 square feet?
100 tiles cover 100 sq ft exactly (with a 1/8-inch grout line, slightly fewer). Add 10% for cuts and breakage and buy 110 — 11 boxes of 10.
How much extra tile should I buy?
10% for a straightforward rectangular room laid straight; 15% for diagonal or herringbone patterns, or rooms with many corners; 20% for large-format tile or complex layouts. Always keep a few spares from the same batch for repairs.
Does the grout gap matter?
A little. A 1/8-inch gap on 12-inch tiles reduces the count by about 2%; on small mosaic or subway tile the effect is bigger. The calculator includes the gap in each tile's footprint.
Are tiles sold by the box or by the tile?
Usually by the box, priced per square foot, with the box coverage printed on the label. Enter the tiles per box to get the box count; you'll round up to whole boxes.
Last updated August 27, 2026.