Blog · 5 min read
How Many Tiles Do I Need? A Worked Example, Start to Finish
A real 10×12 room taken from tape measure to order quantity: net area, waste factor, per-tile coverage, box math, and the attic stock rule.
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Step 1: Net area
Our example room: 10 ft × 12 ft with a 3 × 4 ft closet. Main rectangle is 120 sq ft; the closet adds 12. Nothing permanent sits on the floor, so net area is 132 sq ft.
Step 2: Waste factor
We're laying 12 × 24 porcelain in a straight third-offset pattern — 10% waste is right for straight layouts (diagonal or herringbone would be 15–20%). Order quantity: 132 × 1.10 = 145.2 sq ft. Round to 146.
Waste isn't pessimism — every perimeter row has cuts, you'll break one or two learning the snap cutter, and you want attic stock. Which brings us to the rule pros follow: keep 1–2 boxes after the job. Tile lines get discontinued; a cracked tile in 2029 is only fixable from your own stash.
What else goes in the cart
DGSL Tile Leveling System with Plier, 300 Tile Spacers 1/8" and 100 Wedges
$25.99
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DGSL Tile Leveling System Tile Spacers 1/16 Inch, 300 pieces Horseshoe Shim U Shape Plastic Tile Leveling Clips for Various Types of Tile Leveling
$12.87
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DGSL Tile Spacers 2400 Pcs Tile Clips, Tile Leveling System Clips 1/8 Inch
$35.99
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Prices as of Oct 10, 2026, 6:33 AM UTC. Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product.
Step 3: Tiles and boxes
A 12 × 24 tile covers exactly 2 sq ft. 146 ÷ 2 = 73 tiles. They come 8 per box (16 sq ft per box), so 146 ÷ 16 = 9.1 boxes — order 10 boxes, which is 160 sq ft, giving a comfortable cushion plus attic stock.
That round-up is the step people resist and regret. Being one box short mid-job risks a different dye lot — the same tile from a different production run can be visibly different shade.
Check the dye lot
When the boxes arrive, confirm every box shows the same shade/caliber code before you open them. Mixed lots go back to the store now, not after row four is mortared down.
Do this math on the job site — in the free app
Smart Tile Calculator for Android: offline, in your pocket, free.
FAQ
How many extra tiles should I keep after the job?
One to two boxes, stored flat somewhere dry. They're for future repairs — matching a discontinued tile years later ranges from hard to impossible.
Does grout joint width change tile count?
Negligibly. A 1/8-inch joint on 12-inch tile changes coverage by about 1% — far inside your waste allowance. Ignore it for ordering.
What if boxes cover odd amounts like 10.76 sq ft?
Trust the box coverage number, not your per-tile math — manufacturers pack to nominal coverage. Divide order area by box coverage and round up.
Keep reading
- How to Measure a Room for Tile (Step by Step)
Measure any room for floor or wall tile: handle closets and alcoves, convert inches to decimals, subtract fixtures, and add the right waste percentage.
- Choosing the Right Tile Size for Your Room
How tile size changes a room: when 12×24 beats 4×4, why small rooms can take large tile, grout line math, and the flatness rule for big formats.