Tile Calculator

How to Use This Tile Calculator

Enter your floor or wall dimensions in feet, select your tile size (preset or custom), and choose the grout joint width. The calculator instantly shows the number of tiles needed, how many boxes to buy, and an optional cost estimate — all with your chosen waste factor built in.

The formula is: Area (sq ft) = Length × Width. Number of tiles = Total Area ÷ (single tile area + grout allowance), then multiplied by (1 + waste%). Boxes = ceiling(tiles ÷ tiles_per_box).

How Much Tile Do I Need? The Step-by-Step Formula

Here's the exact math behind tile estimation, broken down so you can verify by hand or understand what our calculator does under the hood:

Step 1: Calculate Total Area

Measure the length and width of your floor (or height and width of each wall section) in feet. Multiply to get square feet. For irregular rooms, divide into rectangles, calculate each separately, and sum them. Pro tip: For wall tile, measure each wall section individually — don't just multiply perimeter by height, because doorways, windows, and alcoves change the count.

Example: A 10′ × 10′ bathroom floor = 100 sq ft. A shower wall that's 5′ wide × 8′ tall = 40 sq ft. A kitchen backsplash 2′ high × 20′ long = 40 sq ft.

Step 2: Calculate Single Tile Coverage (Including Grout)

This is where most DIY tile calculators get it wrong — they ignore grout joint width. Even a 1/8″ grout line adds up across a room. The effective size of each tile is:

Effective length = tile length + grout width
Effective width = tile width + grout width

Then convert to square feet: Single tile coverage = (effective_length × effective_width) ÷ 144 (since tile dimensions are in inches).

Example: 12″×12″ tile with 1/8″ grout → effective size is 12.125″ × 12.125″ = 147.02 sq in ÷ 144 = 1.021 sq ft per tile. That extra 0.021 sq ft per tile adds up to about 2 more tiles per 100 sq ft — our calculator factors this in automatically.

Step 3: Account for Waste

The waste factor covers cuts, breakage, and pattern matching. The industry standard is:

Common Tile Sizes and Their Coverage

Tile Buying Tips: How to Avoid Running Short

1. Always buy from the same dye lot. Tile manufacturers print a lot number on every box. Different dye lots — even of the "same" color — can look noticeably different on your floor. Buy everything at once and check that all boxes share the same lot number. Return unopened boxes after the job if your store allows it.
2. Keep at least one full box for repairs. Tile styles get discontinued. If you crack a tile five years from now, you'll be glad you saved that box in the garage. Write the dye lot number on it so you can try to match if you ever need more.
3. Box labels can be misleading. A box that says "covers 10 sq ft" usually assumes zero grout width and perfect layout. Our calculator gives you a more realistic number that includes grout spacing.
4. For large-format tiles (12×24″ or bigger), buy 15% extra. These tiles are heavier, harder to cut cleanly, and more likely to crack during installation. The extra 5% over the standard waste factor can save you a mid-project trip to the store (where your dye lot might already be sold out).
5. Subway tile math is tricky. At 3″ × 6″ (0.125 sq ft each), a 40 sq ft backsplash needs 320 tiles without waste. With 10% waste and a running bond pattern's end cuts, you'll need about 360-370. Always round up to the next full box.

Floor Tile vs Wall Tile: What's the Difference?

Floor tiles are thicker (typically 8-12mm) with a higher PEI (Porcelain Enamel Institute) wear rating — PEI 3-5 for floors. Wall tiles are thinner (6-8mm), lighter, and rated PEI 0-2. Never use wall tiles on floors — they'll crack under foot traffic. You can, however, use floor tiles on walls (they're just heavier and need a stronger mortar).

Grout Joint Width: The Overlooked Variable

Grout width affects both your tile count and the final look:

• 1/16″ (rectified tile): Only works with precisely cut, rectified tiles that have perfectly square edges. Gives a seamless, modern look. Popular with large-format porcelain.
• 1/8″ (standard): The go-to for most floor and wall tile installations. Wide enough to absorb slight tile size variations, narrow enough to not dominate the look.
• 3/16″–1/4″ (wide): Used for rustic or hand-made tiles where edges aren't perfectly straight. Also common in outdoor installations where thermal expansion is a factor.

Most DIYers can safely use 1/8″ spacing with modern, machine-made tile from any big-box store.

6 Common Tile Installation Mistakes

1. Not checking the subfloor for flatness. Large-format tiles (12×24″+) need a nearly perfectly flat substrate. Any dip or hump over 1/8″ in 10 feet will cause lippage (tile edges that stick up). Use a self-leveling underlayment if needed.
2. Starting from the wall instead of the center. Always snap chalk lines to find the room center and dry-lay a row in each direction. The cut tiles should be at the walls, not in the middle of the room. Adjust your starting point so cut tiles at opposite walls are equal in width.
3. Forgetting to back-butter large tiles. Tiles larger than 12″×12″ should be back-buttered (spreading a thin layer of thinset on the tile back) in addition to notched troweling the floor. This ensures proper coverage and prevents hollow spots.
4. Mixing thinset too dry or too wet. Thinset should hold a notch but still be workable — like peanut butter. Too dry and it won't bond. Too wet and tiles will sink and shift. Follow the bag's water ratio exactly.
5. Walking on tiles too soon. Wait at least 24 hours before walking on newly laid floor tile (48 hours for large format). Grouting can happen after 24 hours, but heavy traffic (appliances, furniture) should wait 72 hours.
6. Skipping the expansion gap. Leave 1/4″ gap around the room perimeter and fill it with caulk (not grout). Tile expands and contracts with temperature changes. Without this gap, tiles can tent and pop off the floor.

You Might Also Need

• Flooring Calculator — Compare tile vs hardwood, laminate, or carpet costs
• Paint Calculator — If you're tiling the walls, you'll probably paint the ceiling
• Concrete Slab Calculator — Make sure your subfloor is solid before tiling
• Drywall Calculator — Prepping a bathroom? You'll need drywall too