How it works
Enter the area to tile, the tile size and the grout joint width. The calculator works out how many tiles fit (each tile plus one joint), adds waste and converts to boxes.
Ten percent waste is standard for square layouts in simple rooms. Use 15% for diagonal layouts, large-format tile or rooms with many cuts, and buy an extra box to keep for repairs.
The thinset estimate assumes a 50 lb bag covering roughly 90 sq ft with a 1/4 × 1/4 in square-notch trowel. A 1/4 × 3/8 in notch, common for 12 in and larger tile, covers only about 60 to 70 sq ft per bag, and a 1/2 in notch for large-format tile about 40 to 45.
Formula
Tiles = area (sq ft) ÷ [(tile length + joint) × (tile width + joint) ÷ 144] × (1 + waste), rounded up.
Questions people ask
How many 12 × 12 tiles do I need for 100 square feet?
About 100 tiles before waste (slightly fewer with grout joints), so buy around 110 with 10% waste.
Should I include the grout joint?
Yes for accuracy. Each tile effectively covers its size plus one joint. For small mosaic or subway tile the joint makes a noticeable difference.
How much extra tile should I buy?
Ten percent for straight layouts, 15% for diagonal or herringbone. Tile is often discontinued, so a spare box saves a mismatched repair later.