Field Guide
How Much Tile Do I Need? Tiles, Thinset & Grout
Tile is sold by the box, and setting it takes thinset mortar and grout. Measure each floor or wall, add waste for your layout, and the tile size, trowel and joint width do the rest.
1. How to Calculate Tile (The Math Explained)
Here's the exact process this calculator uses, with a 12 × 14 ft kitchen floor in 12 × 24 in tile and 1/8 in joints as the example.
-
1
Find the area
Multiply the length by the width. For L-shaped rooms, split the floor into rectangles.
Area = 14 ft × 12 ft = 168 sq ft -
2
Add waste and divide by the tile size
A straight layout needs about 10% extra for cuts. A 12 × 24 in tile is 2 sq ft.
With 10% waste = 168 × 1.10 = 184.8 sq ft Tiles = 184.8 ÷ 2 = 92.4 → 93 tiles -
3
Thinset and grout
Tile this size goes down with a 1/2 × 1/2 in notch trowel, about 40 sq ft per 50 lb bag. Grout fills the joints between tiles.
Thinset = 168 ÷ 40 = 4.2 → 5 bags Grout ≈ 10.3 lb → 1 bag (25 lb)
2. Layouts & Waste
The more angled cuts a layout has, the more tile ends up as offcuts. This calculator sets the waste from the layout you pick.
| Layout | Waste | Notes |
|---|---|---|
| Straight (grid or offset) | 10% | Cuts only at the walls. For plank tile, keep the offset to a third of the length or less. |
| Diagonal | 15% | Tiles turned 45°; every edge piece is a triangle. |
| Herringbone | 20% | Planks in a zigzag; lots of angled cuts at every wall. |
3. Choosing the Trowel and Grout
Bigger tiles need a bigger notch so the mortar covers the whole back of the tile. Thinner joints use unsanded grout; joints 1/8 in and wider use sanded grout.
| Tile size | Trowel notch | Per 50 lb bag |
|---|---|---|
| Under 8 in (mosaic, subway) | 1/4 × 1/4 in square | ~90 sq ft |
| 8 to 15 in (12 × 12) | 1/4 × 3/8 in square | ~60 sq ft |
| 15 in and up (large format, planks) | 1/2 × 1/2 in square | ~40 sq ft |
Pro tip: buy from one lot
Tile color (shade) and size (caliber) vary between production runs. Check that every box has the same lot number, and buy a spare box for future repairs.
4. Frequently Asked Questions
How many tiles do I need for a 5×8 bathroom floor?
A 5 × 8 ft floor is 40 sq ft. Add 10% for cuts and you need 44 sq ft. With 12 × 12 in tiles (1 sq ft each) that's 44 tiles. With 12 × 24 in tiles (2 sq ft each) it's 22.
How much extra tile should I buy?
Buy about 10% extra for a straight layout, 15% for a diagonal layout and 20% for herringbone, since angled cuts create more offcuts. Small or oddly shaped rooms waste more. Keep a spare box from the same lot for future repairs.
How many tiles do I need for a backsplash?
Multiply the length of the counter by the backsplash height. A 15 ft run at 18 in tall is 22.5 sq ft; with 10% waste that's 24.75 sq ft. A 3 × 6 in subway tile is 0.125 sq ft, so you need 198 tiles.
How much thinset do I need?
It depends on the trowel, and the trowel depends on the tile. A 50 lb bag covers about 90 sq ft with a 1/4 × 1/4 in notch (tiles under 8 in), about 60 sq ft with 1/4 × 3/8 in (8 to 15 in tiles) and about 40 sq ft with 1/2 × 1/2 in (large format). 70 sq ft of 12 × 24 in wall tile needs 2 bags. Back-buttering large tiles uses more.
How much grout do I need?
Grout fills the joints, so it depends on the joint width, the tile thickness and how many joints there are. Small tiles have more joints and use far more grout than large ones. 168 sq ft of 12 × 24 in tile with 1/8 in joints takes about 10 lb; the same area of 3 × 6 in subway tile with 1/16 in joints takes about 17 lb.
Should I use sanded or unsanded grout?
Use sanded grout for joints 1/8 in and wider; the sand keeps wide joints from shrinking and cracking. Use unsanded grout for joints narrower than 1/8 in, such as 1/16 in subway tile joints, and on polished stone or glass tile that sand could scratch.
How many square feet are in a box of tile?
It varies by product and size, so check the box or the product page: it lists the square feet per box and the tiles per box. Enter that coverage in the calculator to get the number of boxes.