Tile Calculator

What the Tile Calculator actually computes

The Tile Calculator turns three measurements — floor area, tile size, and waste factor — into one number: how many tiles to buy. The math is small but the consequences of getting it wrong are bigger than they look. Order short, run out mid-job, and your second batch likely comes from a different production run with a slightly different shade. Floor tile doesn't lie about dye-lot drift; the difference shows up under the kitchen light and it shows up forever.

Buy the right amount the first time and you also leave the project with a small reserve. Years from now, when a dropped cast iron pan cracks one tile, you reach into the closet and pull out a perfect match. That's the real reason waste factor exists — half of it is for the cuts during the job, and half of it is for the chips and cracks during the next decade.

The formula is direct: floor area divided by tile area gives the base count, multiplied by one-plus-waste gives the purchase quantity. The calculator handles unit conversion (inches to feet, centimeters to meters) and rounds up so you never end up with 132.4 tiles on a shopping list.

How to use the Tile Calculator

The calculator works in imperial (feet for the room, inches for the tile) or metric (meters and centimeters). Pick the unit set that matches your tape measure.

1. Pick units. US tile is almost always specified in inches; rooms are in feet. Most European tile is centimeters; rooms are in meters.
2. Enter floor dimensions. Length × width. For L-shaped rooms, break into rectangles, calculate each, sum the area, and enter the total as one number.
3. Enter tile size. Read it off the box. Common sizes: 12 × 12 in (the workhorse), 18 × 18 in, 24 × 24 in, 6 × 24 in (plank), 3 × 6 in (subway).
4. Set the waste factor. 10% for straight grid, 15% for diagonal, 20% for herringbone or basketweave.
5. Read the result. Base count (no waste), recommended purchase (with waste), and the rounded-up total.

When you go to the tile store, round up again to the next full box. Tile is sold by the carton (typically 6 to 15 tiles per box depending on size), and the per-tile pricing doesn't change whether you buy 13 boxes or 14.

The formula, with a worked example

Take a 12 × 15 ft room — 180 sq ft of floor. You're laying 12 × 12 in tiles, which is exactly 1 sq ft each. You want 10 percent waste because the layout is a simple straight grid.

1. Floor area: 12 × 15 = 180 sq ft.
2. Tile area: 12 × 12 in = 144 sq in = 1 sq ft.
3. Base tile count: 180 ÷ 1 = 180 tiles.
4. With 10% waste: 180 × 1.10 = 198 tiles.
5. Boxes: if the carton holds 10 tiles, that's 20 boxes (200 tiles total).

Now redo the same room with a herringbone pattern at 20 percent waste. Base 180 tiles, × 1.20 = 216, round up to 220 (22 boxes). The pattern alone cost you 22 extra tiles — about $40-80 in material depending on tile price. The pattern also doubled the install labor. Neither makes herringbone wrong; it just means the budget is bigger than the straight-grid version by a meaningful chunk.

Common tile sizes and their math

Tile sizes don't follow a clean pattern. A few are inherited from old imperial standards, others came from European production lines, others from product designers. Here's the cheat sheet for the sizes you'll meet most often:

Bigger tiles look more modern and have fewer grout lines, but they also reveal floor unevenness — anything more than a 1/8" hump under a 24" tile shows as a rock or a lippage. If the subfloor isn't dead flat, downsize the tile or self-level the slab first.

The waste factor, ranked by layout difficulty

Waste isn't a fudge. It's the predictable percentage of tile that becomes scrap because of cuts at walls, mistakes during install, and the spare bundle you stash for repairs.

The pattern math is straightforward when you watch a tile crew work. In a straight grid, the only cuts happen at the wall — one row across each side. In a diagonal layout, every tile along every wall gets a diagonal cut, which produces a triangular scrap smaller than half a tile (almost always unusable elsewhere). In herringbone, every tile is cut at both ends to fit the pattern, then half the cuts are wrong on the first try.

Small bathrooms break the pattern in the other direction. A 5 × 8 ft bathroom has 40 sq ft of floor but a 26 ft perimeter — that's 0.65 linear ft of perimeter per sq ft of floor, three times worse than a 12 × 15 room. More perimeter means more cuts per area, which means more waste. Bump to 15% for a small bathroom even on a straight grid, and 20% if there's a vanity and toilet creating cutouts.

Walls vs. floors: calculate them separately

A shower wall isn't a floor laid sideways. The tile is usually different (thinner wall tile that won't sag in mastic), the layout often uses smaller tiles for shower walls (3 × 6, 4 × 12, 6 × 6), and the waste profile differs because walls have more obstacles per square foot than floors do.

For a tiled shower, calculate each surface in isolation:

• Floor pan: typically small mosaic on the slope toward the drain. 15% waste because the slopes mean lots of small cuts.
• Three walls: sum the wall area (height × width for each), subtract the door opening, subtract any windows. 10-15% waste.
• Niche / shelves: small but high-cut-percentage surfaces. 20% waste, often using accent tile.
• Ceiling (if tiled): rare but increasing in modern showers. 15% waste; the cuts are awkward overhead.

Sum boxes at the order stage. Most stores won't accept returns on partial boxes, so dial each surface in before placing the order.

Grout: a different calculation entirely

Grout coverage depends on two variables this calculator doesn't ask about: grout line width and tile thickness. A 1 × 1" mosaic with 1/8" grout lines uses more grout per square foot than a 24 × 24" floor tile with 1/16" lines, even though the total floor area is the same. Some quick benchmarks:

The grout manufacturer prints a coverage chart on the bag for the specific product. Match your tile size and grout-line width to their chart, divide your floor area by their coverage, round up by one bag for cleanup losses. Bags are cheap and a half-set batch of grout can't be saved for tomorrow — buy one extra.

When the calculator underestimates

The formula assumes a rectangular room laid out in a rectangular grid with the tile size on the box. Real rooms diverge from that picture in three predictable ways.

• Irregular shapes — L-shapes and U-shapes work if you decompose them into rectangles. Curves and angled walls don't decompose cleanly; add 5% waste for every meaningful diagonal.
• Obstacles — a kitchen with an island, columns, or a peninsula adds cuts around every obstacle. Each one is 4-6 cuts; bump waste by 2-3% per major obstacle.
• Pattern repeats — patterned tile that has to align across the room (think large-format with a printed graphic) requires the layout to start from a chosen anchor, which means more cut-and-discard at the opposite wall. Add 5% beyond the standard layout waste.

For complicated jobs, take a sketch of the floor plan to the tile store. They'll spec the order based on the exact tile you picked and the layout you described. Free service, takes 10 minutes, and the spec usually beats DIY estimates by a few percent.

Buy by the box, always

Tile is sold in cartons. A 12 × 12" floor tile typically comes 10 tiles per box. A 24 × 24" tile is often 3 per box. Subway tile is 30-40 pieces per box. The box yardage is printed on the carton. Three rules for the order:

1. Always round up to the next full box. Partial-box returns get refused at most stores.
2. Buy all boxes from the same shipment. Same shipment usually means same production run, which means same dye lot. Different dye lots show subtle but real color drift.
3. Stash 2-5 spare tiles after the install in their original packaging. They cost almost nothing, and matching tile years later is hard to impossible.

Related calculations

• Square Footage Calculator — for irregular rooms, additions, and combined floor areas.
• Roofing Calculator — same family of "area divided by piece, plus waste" math.
• Concrete Calculator — for the slab work underneath, or a mortar bed in a shower pan.
• Gravel Calculator — for the base layer under an exterior tiled patio.

Frequently asked questions

How do I figure tile count for an L-shaped room?

Break the L into two rectangles, calculate each one's area, add them together, then plug the total into the calculator. The calculator's assumption is rectangular geometry. Curved or angled walls add 3-5% to the waste factor for the extra cuts.

What's the right waste factor for a small bathroom?

15% minimum, even for a straight grid. Small rooms have a high perimeter-to-area ratio, which means more cuts per square foot of finished floor. If the bathroom has a vanity, toilet flange, and shower threshold creating cutouts, go to 20%.

Why round up to a full box instead of buying the exact tile count?

Tile is priced and shipped by the carton. Most stores won't sell partial boxes and won't accept partial-box returns. Buying 132 tiles when the calculator says 132 means walking out with 14 boxes of 10 tiles anyway. Round up at the calculation stage so the spreadsheet matches the order.

Can I mix dye lots if I'm short?

You can; you'll see it. Same tile, same SKU, different production run produces noticeable color drift — usually subtle in the box and obvious on the floor under raking light. The fix is to lay the new dye lot in a separate area (a closet, under a vanity) rather than mixing into the main room. Better to order more upfront.

How much extra do I keep for repairs?

2-5 percent of the original order, in original packaging, stored somewhere flat and dry. Most repairs years later need 1-3 tiles total. Stashing a half-box is enough for any normal household.

What about diagonal vs. straight layout for resale?

Resale doesn't care which layout you picked. Buyers care about clean grout lines, no lippage, and consistent color. A bad straight-grid install looks worse than a good diagonal install. Pick the layout that fits the room — diagonal makes narrow rooms feel wider; straight is the safe default for everything else.

Do I need to plan around the tile size in my room dimensions?

Ideally yes. Pros plan the layout so the cut tiles at opposite walls are roughly equal (a 6-inch cut on one side and a 6-inch cut on the other looks intentional; a full tile on one side and a 2-inch sliver on the other looks like a mistake). Move the starting line around until both edges land at decent widths. The base tile count doesn't change; the symmetry does.

Can the calculator handle wall tile and floor tile in the same project?

One surface at a time. Run the calculator for the floor; run it again for each wall; sum the boxes at the order. Walls and floors usually use different tile (different thickness, different finish), so combining them in one calculation would mislead anyway.