Rectangular Room
Use this form for any plain rectangular floor or wall — most kitchens, bathrooms, and backsplashes. Length × width gives square feet; divide by tile area (in sq ft) and round up after applying the waste factor.
tiles = ⌈ (L × W) / tile_area × (1 + waste%) ⌉
L-Shape Room
Use this form for an L-shaped floor — model the room as two rectangles, enter each pair, and the calculator sums the areas before computing tile count. Same waste-factor math, just a two-rectangle starting area.
tiles = ⌈ ((L₁ × W₁) + (L₂ × W₂)) / tile_area × (1 + waste%) ⌉
How It Works
This tile calculator computes how many tiles you need to cover a floor or wall, plus optional box count and grout-bag estimate. Enter the room dimensions (rectangle or L-shape — the calculator sums the two rectangles for L-shapes), pick a standard tile size (12 × 12 is most common) or enter a custom size in inches, and choose a waste factor: 10% is standard for a straight grid layout, 15% for diagonal layouts, and 20% for mosaic or herringbone patterns where cut-tile waste runs higher. The hero number is the total tile count (always rounded up); supply tiles_per_box and grout-bag coverage to also get the box count and grout estimate.
Example Problem
How many 12-inch × 12-inch tiles are needed for a 12 ft × 15 ft kitchen floor with a 10% waste factor, sold in boxes of 12 tiles, plus grout for the 1/4-inch joints?
- Knowns: room shape = rectangle, L = 12 ft, W = 15 ft, tile = 12 in × 12 in, waste factor = 10%, tiles per box = 12.
- Room area: A = L × W = 12 × 15 = 180 sq ft.
- Tile area in sq ft: A_tile = (12 × 12) / 144 = 1.0 sq ft per tile.
- Raw tile count: ⌈ 180 / 1.0 ⌉ = 180 tiles.
- With 10% waste: ⌈ 180 × 1.10 ⌉ = ⌈ 198 ⌉ = 198 tiles.
- Boxes needed: ⌈ 198 / 12 ⌉ = 17 boxes (you'll have 4 spare tiles for future repairs).
- Grout: a 25 lb premix bag covers ~75 sq ft at a 1/4-inch joint, so ⌈ 180 / 75 ⌉ = 3 bags.
Save the spare tiles after the install — dye lots vary between production runs, and a chipped tile two years later is much easier to replace from your own attic than to match at the store.
When to Use Each Variable
- Rectangular Floor or Wall — for any plain rectangular surface — kitchen floors, bathroom floors, shower walls, backsplashes, fireplace surrounds. The most common case; pick this whenever the room is one rectangle.
- L-Shaped Room — for an L-shaped floor — model the room as two rectangles (decompose along the inside corner). Enter each pair of dimensions; the calculator sums the areas before applying the tile size and waste factor.
Key Concepts
Tile area is calculated in square feet (tile_in_w × tile_in_h / 144 = sq ft per tile). Raw tile count is the room area divided by tile area, rounded UP — you cannot buy a partial tile. The waste factor is then multiplied in BEFORE the final ceil, so cut-tile waste is properly absorbed: 10% for straight grid layouts (the manufacturer default), 15% for diagonal layouts (more triangular cuts at the walls), and 20% for mosaic or herringbone where cuts at every course compound. Box count uses the same ceil rule — ordering 17 boxes when you need 16.5 is correct; you can't return half a box, and the extras are your future repair stock (dye lots vary between production runs). Pre-mixed grout in 25 lb bags covers about 75 sq ft at a 1/4-inch joint with standard 12-inch tiles; wider joints, larger tiles, or deeper bond beds reduce coverage. For most residential tile jobs, 1 to 3 bags of grout is enough.
Applications
- Kitchen and bathroom floors (12 × 12 or 12 × 24 tile, straight grid)
- Shower walls and tub surrounds (4 × 4, 6 × 6, or subway 3 × 6 tile)
- Backsplashes and accent walls (mosaic sheets or 4 × 4 tile, sometimes diagonal)
- Fireplace surrounds and hearths (large-format 12 × 24 or 24 × 24 tile)
- Entryway and mudroom floors (porcelain 12 × 12 or 18 × 18 for durability)
- Outdoor patios and pool decks (slip-rated 12 × 12 or 16 × 16 porcelain)
- Commercial restrooms and lobbies (high-traffic 12 × 12 or 18 × 18 porcelain)
- Herringbone and chevron pattern feature walls (rectangular 4 × 12 or 6 × 24 tile)
Common Mistakes
- Skipping the waste factor — 0% waste leaves no cushion for cut-tile waste, breakage during install, or future repair tiles. 10% is the absolute minimum for a straight grid.
- Using 10% waste on a diagonal or herringbone layout — diagonal cuts at walls and the multi-direction cuts in herringbone routinely produce 15-20% waste. Pick the right waste factor for the pattern.
- Forgetting that tile size is in INCHES while room dimensions are in FEET — the calculator handles the unit math (divides by 144 internally), but verify the tile dimensions are entered correctly.
- Rounding box count down to save money — a single short box means stopping the job to drive to the store, and the new box may be from a different dye lot that doesn't match.
- Not buying spare tiles for future repairs — keep at least 5-10% extra after the install. Replacement tile from a future store visit will be a different dye lot and will be visibly different from the surrounding floor.
- Confusing nominal tile size with actual tile size — a '12 inch' tile is actually 11-7/8 inch or 11-15/16 inch (the grout joint fills the difference). For a count estimate the nominal size is correct; for a wall layout, work from the actual size plus the joint width.
Frequently Asked Questions
How many tiles do I need?
Compute tiles = ⌈ room_area / tile_area × (1 + waste%) ⌉. For a 12 × 15 ft room (180 sq ft) with 12 × 12 in tiles (1 sq ft each) and 10% waste, that's ⌈ 180 × 1.10 ⌉ = 198 tiles. Always round up — partial tiles can't be bought, and the waste factor covers cuts, breakage, and future repairs.
What waste % should I use for tile?
Use 10% for a straight grid layout (the manufacturer default and the safe choice for most kitchens and bathrooms). Use 15% for diagonal layouts because the angled wall cuts produce more triangular waste. Use 20% for mosaic or herringbone patterns where every course has cuts at multiple angles. For very complex layouts (chevron, pinwheel, mixed sizes), some installers go as high as 25%.
How many tiles in a box?
It depends on the tile size. Common box counts: 12 × 12 in tile → ~12 per box (12 sq ft), 6 × 6 in tile → ~33 per box (~8 sq ft), 12 × 24 in tile → ~8 per box (16 sq ft), 24 × 24 in tile → ~3 per box (12 sq ft). The exact count is printed on the box; enter it in the 'tiles per box' field and the calculator returns ⌈ tiles_needed / tiles_per_box ⌉ boxes.
How much grout do I need for X tiles?
The simple rule of thumb is one 25 lb bag of pre-mixed grout per 75 sq ft of floor at a 1/4-inch joint with 12-inch tiles. A 12 × 15 ft (180 sq ft) floor needs ⌈ 180 / 75 ⌉ = 3 bags. Coverage drops with larger tiles (less linear feet of joint per sq ft), wider joints, or deeper bond beds. For small backsplashes (< 30 sq ft) one bag is almost always enough.
Diagonal vs straight tile layout — which uses more tile?
Diagonal layouts use about 5% more tile than straight grid because the wall cuts produce more triangular waste pieces that can't be reused elsewhere. Use a 15% waste factor for diagonal versus the standard 10% for straight grid. Visually a diagonal layout makes a small room feel larger because the long sight-lines run corner-to-corner; the extra tile is usually worth it.
How do I calculate subway tile count?
Subway tile is just a rectangular tile in a brick-pattern offset — the math is identical to a straight grid. For a 3 × 6 in tile, A_tile = (3 × 6) / 144 = 0.125 sq ft. A 30 sq ft backsplash needs ⌈ 30 / 0.125 ⌉ = 240 tiles raw, or ⌈ 240 × 1.10 ⌉ = 264 tiles with 10% waste. The brick offset doesn't add waste — every cut tile from one course can be used to start the next.
How do I tile an L-shaped room?
Decompose the L into two rectangles by drawing a line at the inside corner. Enter each rectangle's length and width in the L-shape form — the calculator computes (L₁ × W₁) + (L₂ × W₂) for the total area, then divides by the tile area and applies the waste factor. Same math as a single rectangle, just with a two-piece starting area.
Should I buy extra tile beyond the waste factor?
Yes — keep at least 5-10 tiles in the attic after the install as your future repair stock. Tile dye lots vary between production runs, and a chipped or cracked tile two years later is far easier to replace from your own spares than to color-match at the store. The 10% waste factor already absorbs cut waste; the spare stock is on top of that.
Reference: Tile Council of North America (TCNA) Handbook for Ceramic, Glass, and Stone Tile Installation — waste-factor and grout-coverage standards. Manufacturer technical data for Quikrete and Mapei pre-mixed grout (75 sq ft per 25 lb bag at 1/4-inch joint with 12-inch field tile).
Worked Examples
Kitchen Floor
How many 12 × 12 in tiles for a 12 × 15 ft kitchen at 10% waste?
A 12 ft × 15 ft kitchen tiled with 12-inch porcelain on a straight grid. Standard residential job — apply 10% waste, report tile count, box count (12 tiles per box), and grout-bag estimate.
- Room area: 12 × 15 = 180 sq ft
- Tile area: (12 × 12) / 144 = 1.0 sq ft per tile
- Raw count: ⌈ 180 / 1.0 ⌉ = 180 tiles
- With 10% waste: ⌈ 180 × 1.10 ⌉ = 198 tiles
- Boxes: ⌈ 198 / 12 ⌉ = 17 boxes
- Grout: ⌈ 180 / 75 ⌉ = 3 bags (25 lb premix at 1/4 in joint)
198 tiles (17 boxes), plus 3 bags of grout
Save the spare tiles after the install — dye lots vary, so future repair tiles from the store won't perfectly match.
Bathroom Floor (diagonal)
How many 6 × 6 in tiles for an 8 × 10 ft bathroom on a 45° diagonal?
An 8 ft × 10 ft bathroom tiled with 6-inch ceramic on a 45° diagonal. Diagonal layouts produce more wall cuts — bump waste to 15%.
- Room area: 8 × 10 = 80 sq ft
- Tile area: (6 × 6) / 144 = 0.25 sq ft per tile
- Raw count: ⌈ 80 / 0.25 ⌉ = 320 tiles
- With 15% waste (diagonal): ⌈ 80 / 0.25 × 1.15 ⌉ = ⌈ 368 ⌉ = 368 tiles
- Boxes (33 per box): ⌈ 368 / 33 ⌉ = 12 boxes
- Grout: ⌈ 80 / 75 ⌉ = 2 bags
368 tiles (12 boxes), plus 2 bags of grout
The diagonal eats more tile but visually elongates the room — a worthwhile trade-off for small bathrooms where straight grid can feel cramped.
Subway Tile Backsplash
How many 3 × 6 in subway tiles for a 30 sq ft kitchen backsplash?
A 30 sq ft kitchen backsplash done in classic 3 × 6 in subway tile, brick offset. Subway is technically a custom size — enter 3 in × 6 in tile dimensions.
- Treat the backsplash as one rectangle (e.g., 10 ft × 3 ft = 30 sq ft)
- Tile area: (3 × 6) / 144 = 0.125 sq ft per tile
- Raw count: ⌈ 30 / 0.125 ⌉ = 240 tiles
- With 10% waste: ⌈ 240 × 1.10 ⌉ = 264 tiles
- Brick offset doesn't add waste — cuts from one course start the next
- Grout: 1 bag (< 75 sq ft) is plenty for a backsplash
264 tiles, 1 bag of grout
Standard subway is 3 × 6 in, but 4 × 8 in 'modern subway' and 4 × 12 in 'tall subway' are also common — switch the tile size and the same formula applies.
Tile Calculator Formulas
Tile count starts from the room area (in square feet) and the tile area (also in square feet). The waste factor is multiplied in BEFORE the final ceiling, so cut-tile waste is properly absorbed. Box count and grout estimate use the same ceil rule — partial boxes and partial bags don't exist.
Room area (rectangle): A = L × W
Room area (L-shape): A = (L₁ × W₁) + (L₂ × W₂)
Tile area: A_tile = (w_in × h_in) / 144
Tiles = ⌈ A / A_tile × (1 + waste% / 100) ⌉
Boxes = ⌈ Tiles / tiles_per_box ⌉
Grout bags = ⌈ A / coverage_per_bag ⌉
Where:
- A — room area (sq ft)
- L, W — room length and width (any matching unit; ft is the canonical)
- w_in, h_in — tile width and height in INCHES (divide by 144 to convert to sq ft)
- waste% — buffer percentage: 10 (straight grid), 15 (diagonal), 20 (mosaic / herringbone)
- tiles_per_box — printed on the carton (e.g., 12 per box for 12 × 12 tile)
- coverage_per_bag — ~75 sq ft per 25 lb premix bag at 1/4-inch joint with 12-inch tile
Standard Tile Sizes Reference
| Nominal Size | Sq ft / tile | Tiles / 100 sq ft | Typical Use |
|---|---|---|---|
| 4 × 4 in | 0.111 | 900 | Backsplash, accent walls |
| 6 × 6 in | 0.25 | 400 | Shower walls, small bathrooms |
| 8 × 8 in | 0.444 | 225 | Mudroom, laundry |
| 12 × 12 in | 1.0 | 100 | Kitchen, bathroom (most common) |
| 12 × 24 in | 2.0 | 50 | Modern floors, plank look |
| 16 × 16 in | 1.778 | 57 | Entryway, mid-size floors |
| 18 × 18 in | 2.25 | 45 | Living room, foyer |
| 24 × 24 in | 4.0 | 25 | Large-format modern floors |
| 24 × 48 in | 8.0 | 13 | Slab look, commercial lobbies |
Tiles per 100 sq ft is the raw count (no waste). Multiply by 1.10, 1.15, or 1.20 and round UP for the actual order quantity at 10%, 15%, or 20% waste.
Related Calculators
- Square Footage Calculator — compute room area in sq ft for rectangle, L-shape, or multi-room layouts
- Concrete Volume Calculator — the same waste-factor + bag-count pattern, applied to concrete pours
- Rectangle Calculator — solve length, width, area, perimeter, or diagonal of a rectangle
- Area Converter — switch between sq ft, sq m, sq yd, and other area units
- Length Converter — convert inches, feet, meters, and yards before entering dimensions
Related Sites
- Dollars Per Hour — Weekly paycheck calculator with overtime
- Percent Off Calculator — Discount and sale price calculator
- BOGO Discount — Buy-one-get-one discount calculator
- Compare 2 Loans — Side-by-side loan comparison calculator
- Temperature Tool — Temperature unit converter
- Z-Score Calculator — Z-score, percentile, and probability calculator