Tile Calculator guide
Work out how many tiles and boxes to buy for a floor, shower wall, or backsplash. Enter the area and tile size, set the grout joint and layout, and the calculator adds the right waste factor and rounds up to full boxes.
How to measure for tile
For a floor, measure the length and width of the room in feet and multiply. For a wall or a backsplash, measure the width and the height you plan to tile. Then subtract anything that will not get tile: a bathtub, a kitchen island, built-in cabinets. The calculator has a deduct box for exactly that.
Write down the actual tile size too, not just the name on the shelf tag. A tile sold as 12 × 24 may really be 11.8 × 23.6 inches, and a 4 × 4 wall tile is usually 4.25 inches square. On a big floor that difference adds up to several tiles.
The formula, including grout
Each tile covers its own face plus half the grout joint on each side, which works out to (tile width + joint) × (tile length + joint). Divide that by 144 to get square feet per tile. Divide the area by that number, add waste, and round up. Then divide by tiles per box and round up again.
Most calculators ignore the grout joint. On large tiles with a 1/8-inch joint it barely matters, but on small tiles with wide joints it does: a 4 × 4 tile with a 1/4-inch joint covers 13% more area than the tile alone. Joint width is set by the tile, not by taste. Rectified porcelain can go down to 1/16 or 1/8 inch; handmade or pillowed tile often needs 3/16 to 1/4 inch. Check the box.
Worked example: a 12 × 10 bathroom floor
Say the floor is 12 × 10 ft, or 120 sq ft, and you want 12 × 24 inch porcelain with a 1/8-inch joint. Each tile covers 12.125 × 24.125 ÷ 144 = 2.03 sq ft. So 120 ÷ 2.03 = 59.1 tiles for a perfect, no-cut job.
Add 10% for a straight or brick-offset layout and it becomes 65 tiles. At 8 tiles per box, that is 8.1 boxes, so you buy 9 boxes, or 72 tiles. The seven spares are not waste; they are the replacements you will be grateful for when a dropped pan cracks a tile in five years and the style is discontinued.
Lay the same floor on a 45° diagonal and waste goes to 15%, which is 68 tiles and still 9 boxes. Herringbone at 20% needs 71 tiles, which is still 9 boxes, but only just.
Choosing the waste percentage
10% is the standard for straight and offset patterns in a normal room. Go 15% for diagonal layouts, because every edge piece is a triangle cut. Go 20% for herringbone, chevron, or rooms with lots of corners, pipes, and doorways. Large-format tiles (15 inches and up) can need more than their pattern suggests because one bad cut wastes a big, expensive piece. A plain rectangle with a layout that happens to land on full tiles can get away with 5%, but it is rare.
Common mistakes
Buying boxes from different lots. Tile color and even size vary between production runs. Check the lot or shade number on every box before you leave the store.
Forgetting setting materials. Tile is only part of the bill. You also need thinset (large tiles need a bigger trowel notch, which roughly halves the coverage per bag), grout, spacers, and leveling clips for anything over about 15 inches.
Skipping the dry layout. Lay a row of tiles out before you mix thinset. Centering the pattern so you do not end with a 1-inch sliver along a visible wall is worth 15 minutes of planning.
Tiling over flexible floors. Tile cracks on subfloors that bounce. Large-format tile in particular needs a stiff, flat substrate.
When to hire a pro
A backsplash or a small floor is a good first tile project. Hire a tile setter for showers (waterproofing mistakes cause rot you will not see for years), large-format tiles over 24 inches, natural stone, heated floors, and any floor that needs leveling first. The Tile Council of North America publishes the installation methods pros follow, and a good installer will know which one fits your substrate.
How we calculate: sources
Frequently asked questions
How do I calculate how many tiles I need?
Divide the area by the coverage of one tile including its grout joint, then add waste and round up. For 120 sq ft of 12 × 24 in tile with a 1/8 in joint, each tile covers 2.03 sq ft, so you need 59 tiles plus 10%, or 65.
How much extra tile should I buy?
About 10% for straight or brick-offset layouts, 15% for diagonal layouts, and 20% for herringbone or chevron. Keep the spare tiles; matching a discontinued tile years later is often impossible.
How many 12x24 tiles are in a box?
Commonly 8 tiles, or 16 sq ft per box, but it varies by brand and thickness; some boxes hold 6 or 7. Enter the count printed on the box you are buying.
Does grout width change how many tiles I need?
Slightly. Each tile covers its face plus the joint, so wider joints mean fewer tiles. It matters most with small tiles: a 1/4 in joint on 4 × 4 in tile adds about 13% coverage per tile.
What size grout joint should I use?
Follow the tile maker's recommendation. Rectified porcelain can use 1/16 to 1/8 in joints; most floor tile uses 1/8 to 3/16 in; handmade or uneven tile often needs 1/4 in. Joints 1/8 in and wider usually take sanded grout.
How much thinset do I need?
A 50 lb bag covers roughly 80 to 95 sq ft with a 1/4 in square-notch trowel and about 40 to 50 sq ft with the 1/2 in notch large tiles need. Check the coverage chart on the bag for your trowel size.
Is my tile project data private?
Everything runs in your browser. Nothing you enter is uploaded to a server or stored by us.