Running out of tile halfway through a job is one of the most frustrating things that can happen in a remodel. The store may not have more. If it does, the new boxes might come from a different dye lot, and the color will not match. On the other side, buying far too much wastes money, since many stores will not take back opened boxes or special-order tile.

Getting the number right is not hard once you know the steps. This guide covers how to measure floors and walls, how much extra to add for waste, how tile size and pattern change your order, and how to estimate grout, thinset, and other supplies.

Step 1: Measure the Floor

For a simple rectangular floor, multiply length by width.

Example: A bathroom that is 8 feet long and 5 feet wide has 40 square feet of floor.

Most bathrooms are not perfect rectangles. You might have a closet nook, an angled wall, or a bump-out. Break the room into smaller rectangles, measure each one, and add them together.

Should you subtract the space under the vanity and toilet? For the toilet, no. Tile goes under it. For the vanity, it depends. A freestanding or wall-hung vanity needs tile beneath it. A built-in cabinet with a toe kick usually does not, though some installers tile under it anyway so you can change vanities later without patching the floor. When in doubt, tile it all.

Step 2: Measure the Walls

Wall tile is measured the same way, one wall at a time. Multiply the width of each wall by the height you plan to tile.

Common wall tile heights:

Tub surround: about 60 to 72 inches above the tub, or up to the ceiling
Walk-in shower: usually floor to ceiling, often 96 inches
Wainscot around the room: often 36 to 48 inches
Backsplash behind a vanity: 4 to 18 inches, or up to the mirror

Subtract large openings like windows and the shower entry. Do not bother subtracting small things like a shower valve or niche. The niche actually adds tile, since you need to cover its back and sides.

Example: A standard 60 inch alcove tub has a back wall about 60 inches wide and two side walls about 30 inches deep. Tiling to 84 inches high:

Back wall: 5 ft x 7 ft = 35 sq ft
Two side walls: 2.5 ft x 7 ft x 2 = 35 sq ft
Total: 70 sq ft

Step 3: Add Extra for Waste and Cuts

You will never use every tile at full size. Tiles get cut at walls, around the toilet flange, and around pipes. Some will chip or crack. And you want a few spares for future repairs.

Here is a general guide for overage:

Layout	Add This Much
Straight lay, simple room	10%
Straight lay, many corners or cutouts	12% to 15%
Offset or brick pattern	10% to 15%
Diagonal layout	15%
Herringbone or chevron	15% to 20%
Large format tile (24 inch and up)	15% to 20%
Natural stone with color variation	15%

Large tiles need more coverage than you might think. When a cut piece is too small to use elsewhere, a big chunk of an expensive tile goes in the trash.

Example: 40 sq ft floor with a straight lay at 10% waste: 40 x 1.10 = 44 sq ft.

Step 4: Convert to Boxes

Tile is sold by the box, and each box lists how many square feet it covers. Divide your total by the coverage per box and round up.

Example: You need 44 sq ft. Each box covers 10.76 sq ft. 44 / 10.76 = 4.09, so you buy 5 boxes.

Always round up. Never round down on tile.

If you would rather not do the math by hand, a tile calculator can handle the room dimensions, tile size, pattern, and waste percentage for you, then tell you how many boxes to buy. It is a good way to double check your numbers before you order.

How Tile Size Changes the Job

Tile size affects more than the count. It changes the labor, the setting material, and how flat the surface has to be.

Small mosaics (1 to 2 inch): Usually come on mesh sheets about 12 by 12 inches. Great for shower floors because the many grout lines give grip and let the tile follow the slope to the drain. They use more grout.

Standard sizes (3×6 subway, 12×12, 12×24): Easy to work with and widely available. The 3×6 subway is still one of the most common shower wall tiles.

Large format (24×24, 24×48, and up): Fewer grout lines and a clean look. They need a very flat substrate, a large-notch trowel, and often a leveling system. Not ideal for shower floors because they cannot follow the slope well.

Estimating Grout

Grout depends on tile size, joint width, and tile thickness. Smaller tiles and wider joints use more grout. Most grout bags print a coverage chart on the back.

Rough numbers for a 25 lb bag of sanded grout with 1/8 inch joints:

12×12 tile: about 150 to 200 sq ft
3×6 subway: about 60 to 80 sq ft
2×2 mosaic: about 35 to 50 sq ft

For a typical small bathroom floor and tub surround, one or two bags is usually enough. Buy an extra small bag of the same color for touch-ups.

Estimating Thinset Mortar

A 50 lb bag of thinset covers roughly:

1/4 x 1/4 inch notch trowel: 80 to 95 sq ft
1/2 x 1/2 inch notch trowel: 40 to 50 sq ft

Larger tiles need bigger notches. Back-buttering large tiles, which most installers do, also uses more mortar. Plan for an extra bag.

Other Supplies to Add to Your List

Cement board or foam board for walls and floors in wet areas
Waterproofing membrane (liquid or sheet) for showers and tub surrounds
Uncoupling membrane for floors over wood subfloors, if your installer uses one
Tile edge trim (metal or PVC) for exposed edges
Spacers or a leveling clip system
Silicone caulk for corners and where tile meets the tub
Grout sealer if you use a cement-based grout

Common Mistakes to Avoid

Measuring once. Measure twice, and write everything down on a simple sketch.
Ignoring dye lots. Check that every box has the same lot number before you leave the store.
Forgetting the niche and curb. A shower niche and curb can add 5 to 10 sq ft.
Using the same waste factor for every pattern. Herringbone eats tile.
Throwing out leftovers. Keep a box of extras in the attic or garage. If a tile cracks years from now, you will be glad you have a match.

A Quick Worked Example

Let’s put it together for a 5×8 bathroom with a tiled floor and a tub surround.

Floor: 40 sq ft, straight lay 12×24 porcelain, 12% waste = 44.8 sq ft. Boxes cover 15.5 sq ft each. 44.8 / 15.5 = 2.9, so 3 boxes.
Tub walls: 70 sq ft of 3×6 subway, 10% waste = 77 sq ft. Boxes cover 12.5 sq ft. 77 / 12.5 = 6.2, so 7 boxes.
Niche: add 1 extra box of subway.
Grout: 2 bags.
Thinset: 3 bags (one for floor, two for walls).

That is a clear shopping list with a small buffer built in.

Final Thoughts

Tile math comes down to three things: careful measurements, the right waste factor for your pattern, and rounding up to full boxes. Take the time to sketch the room, check your numbers with a calculator, and buy everything from the same lot. Your installer will thank you, and you will not be stuck hunting for one more box halfway through grouting.