How Much Tile Do I Need? Formula, Waste and Examples (2027)

How much tile do you need? The short answer

Tile needed = (length × width) × (1 + waste %) ÷ coverage per carton, always rounded up to whole cartons. Use 10% waste for a straight lay, 15% for diagonal, and 15-20% for herringbone or small rooms with many cuts. A 12 × 14 ft room with 10% waste and 20 sq ft cartons needs 10 cartons.

That is the whole method. The rest of this guide shows the arithmetic, the rounding, and the places where people end up a carton short.

The formula in one line

1. Area = length × width (subtract large areas you will not tile).
2. Area with waste = area × (1 + waste %). For 10% waste, multiply by 1.10.
3. Cartons = area with waste ÷ coverage per carton, rounded up.

The coverage per carton is printed on the box or the product page (for example "20 sq ft per carton" or "1.44 m² per carton"). Always buy against that number, not against a tile count you worked out yourself. Step 3 explains why.

Quick reference table: room size to cartons

These examples assume a straight lay, 10% waste and 20 sq ft cartons. Replace the carton size with your own.

Room	Area	Area + 10%	Cartons (÷ 20)	Rounded up	Tile bought
5 × 8 ft bath	40 sq ft	44 sq ft	2.2	3	60 sq ft
10 × 12 ft	120 sq ft	132 sq ft	6.6	7	140 sq ft
12 × 14 ft	168 sq ft	184.8 sq ft	9.24	10	200 sq ft
15 × 20 ft	300 sq ft	330 sq ft	16.5	17	340 sq ft

Notice the 5 × 8 ft bath: 2.2 cartons becomes 3, so you buy 20 sq ft more than the raw area. Small rooms round up the most, in proportion.

Step 1: Measure the area (sq ft and m²)

Measure the surface you will actually tile, not the room as drawn on a floor plan. Measure each dimension twice, at more than one point, because walls are rarely perfectly parallel.

Rectangular rooms

Area = length × width. A 12 × 14 ft room is 12 × 14 = 168 sq ft. Convert inches to decimal feet before multiplying: 11 ft 8 in is 11 + (8 ÷ 12) = 11.67 ft. Do not type 11.8 for 11 ft 8 in.

L-shaped rooms and alcoves

Split the shape into rectangles, calculate each, and add them. Take a 14 × 12 ft space with a 6 × 5 ft corner missing:

• Strip A: 14 ft × 7 ft = 98 sq ft
• Strip B: 8 ft × 5 ft = 40 sq ft
• Total: 98 + 40 = 138 sq ft

Check it the other way: the full 14 × 12 rectangle is 168 sq ft, minus the 6 × 5 notch (30 sq ft) is also 138. If both routes agree, your measurements are consistent. With 10% waste that is 151.8 sq ft, and with 20 sq ft cartons, 7.59, so 8 cartons.

Subtracting doors, tubs and built-ins

• Floors: subtract areas that will not be tiled, such as a tub footprint or a built-in cabinet base. A 9 × 10 ft bathroom (90 sq ft) with a 5 × 2.5 ft tub (12.5 sq ft) is 77.5 sq ft. Tile usually runs through a doorway, so do not subtract door openings.
• Walls: subtract windows and doors that are clearly larger than a few square feet.
• Small cut-outs: do not subtract outlets, vents or a niche-sized gap. Cutting around them creates waste, so subtracting them usually leaves you short.

How to calculate the square metre of a room

Multiply the two sides in metres. A room 3.6 m × 4.2 m is 3.6 × 4.2 = 15.12 m². Measuring in millimetres? Divide by 1,000 first (3,600 mm = 3.6 m). To convert, 1 sq ft is about 0.0929 m², so the 168 sq ft room above is roughly 15.6 m².

Step 2: Add the right waste percentage

Waste covers cuts at edges, tiles broken in handling, and tiles you reject for chips or shade. It is added to the area, not to the number of cartons.

Waste by layout pattern

These are common rules of thumb, not guarantees. If your installer or the manufacturer gives a different figure, use theirs.

Layout	Typical waste
Straight (grid) lay	10%
Running bond / brick, offset	10-12%
Diagonal	15%
Herringbone	15-20%
Very small room or many cuts	Add more than the base rate

Diagonal and herringbone patterns waste more because nearly every edge tile is cut at an angle, and the offcut often cannot be reused.

When to go higher

Add more than the base rate when:

• The room has many corners, columns, curves or angled walls.
• The tile is large format (24 × 24 in or bigger) and the room is small, so few offcuts are reusable.
• The tile is natural stone or handmade, where you will cull pieces for shade or chips.
• The room is out of square, which makes edge cuts uneven (more on this below).
• It is your first tiling job.

Keep a spare carton for repairs and dye lots

Tile is made in production lots, and shade can differ between them. Buy everything for a room in one order so the cartons share a lot number, and check the numbers when they arrive. Keeping one spare carton (or at least a few loose tiles) lets you repair a cracked tile years later, when the same lot may be discontinued. Our dye lot tracking guide covers lot matching in more depth.

Step 3: Convert to tiles or cartons (and round up)

There are two ways to get from area to a purchase quantity. Both should land on about the same answer if you use the same carton.

Method A: by carton coverage

Worked example: 12 × 14 ft room, 10% waste, 20 sq ft cartons.

1. Area: 12 × 14 = 168 sq ft
2. With waste: 168 × 1.10 = 184.8 sq ft
3. Cartons: 184.8 ÷ 20 = 9.24
4. Round up: 10 cartons = 200 sq ft

You end up with 200 - 184.8 = 15.2 sq ft more than your waste-adjusted estimate, and 32 sq ft more than the bare room area. That surplus is your cushion for repairs.

If you are buying flooring-style boxes, our flooring box calculator gives a quick box count (it is built for flooring, so check the numbers against tile cartons).

Method B: by tile size and count per sq ft

Tiles per sq ft = 1 ÷ area of one tile in sq ft.

Tile size	Area per tile	Tiles per sq ft
12 × 12 in	1 sq ft	1
12 × 24 in	2 sq ft	0.5
24 × 24 in	4 sq ft	0.25
6 × 6 in	0.25 sq ft	4
3 × 6 in	0.125 sq ft	8
4 × 4 in	0.111 sq ft	9

Worked example with 12 × 24 in tile in the same 168 sq ft room:

1. Tiles for the area: 168 ÷ 2 = 84 tiles
2. With 10% waste: 84 × 1.10 = 92.4, rounded up to 93 tiles
3. If a box holds 8 tiles: 93 ÷ 8 = 11.6, rounded up to 12 boxes

Why you can't buy 8.4 cartons

Cartons are sold whole, and tile is rarely sold loose from an opened box. So any fractional answer rounds up, even 9.01. Rounding down leaves you short, and a reorder may come from a different lot.

Why do the two methods give 10 and 12? Because the cartons are different. In Method A the carton covers 20 sq ft. In Method B, 8 tiles × 2 sq ft is only 16 sq ft per box. Run Method A with a 16 sq ft carton and you get 184.8 ÷ 16 = 11.55, which rounds up to 12. Same answer.

In practice, nominal tile sizes are often not the real sizes. A "12 × 24" porcelain tile may measure 11.81 × 23.62 in (about 1.94 sq ft), and manufacturers print carton coverage after accounting for that. Carton coverage is the number to trust, because it is what the box actually contains.

Grout joints and the 3/4/5 rule explained

Grout joints. Each tile effectively covers its own size plus half a joint on each side. With 12 × 24 in tiles and 3/16 in joints, each tile covers 12.1875 × 24.1875 in, about 2.05 sq ft instead of 2. That is roughly 2% less tile. On large tiles with narrow joints the effect is small and the waste allowance absorbs it. On small tiles and mosaics with wide joints it matters more. Check whether the stated carton coverage already assumes a joint.

The 3/4/5 rule. This is not a quantity formula. It is a way to check that a corner is square, or to snap a square starting line before you lay tile. Measure 3 ft along one wall and 4 ft along the other from the corner. If the diagonal between those two marks is exactly 5 ft, the corner is 90 degrees. Multiples work too (6-8-10, 9-12-15), and larger multiples are more accurate.

It matters for quantity because an out-of-square room produces tapered edge cuts, and those waste more tile than a square one. If your check is off by more than a small amount, move to the higher end of your waste range.

Worked examples for common rooms

All values below are examples. Replace them with your own measurements and carton coverage.

Bathroom floor (5 × 8 ft)

• Area: 5 × 8 = 40 sq ft
• 15% waste (small room, many cuts): 40 × 1.15 = 46 sq ft
• Cartons at 15.5 sq ft each: 46 ÷ 15.5 = 2.97, rounded up to 3 cartons (46.5 sq ft)

Three cartons leaves only 0.5 sq ft above the estimate. If the layout is diagonal or the tile is hard to match later, a fourth carton is a sensible call.

Kitchen backsplash and wall tile (height × width minus openings)

Wall tile uses the same formula, but measure height × width for each wall section.

• Backsplash: 30 in high = 2.5 ft, 10 ft wide, 2.5 × 10 = 25 sq ft
• Minus a 2 × 2 ft window: 25 - 4 = 21 sq ft
• With 10% waste: 23.1 sq ft. With 15%: 24.15 sq ft
• Cartons at 10 sq ft: 2.31 or 2.42, either way 3 cartons

Wall tile is cut around outlets, switches and corners, and small formats like subway tile are easier to cut, so 10% is often enough for a straight stack. Diagonal or herringbone patterns push it to 15-20%.

Shower walls

Add each wall you will tile. For a 3 × 3 ft shower with three tiled walls up to 7 ft:

• Back wall: 3 × 7 = 21 sq ft; two side walls: 21 sq ft each
• Total: 63 sq ft
• With 15% waste: 72.45 sq ft
• Cartons at 12 sq ft: 72.45 ÷ 12 = 6.04, which is 7 cartons

Six cartons would cover 72 sq ft, a hair short. With niches, a bench or diagonal cuts, going to 7 is the safer order. Add the shower floor separately, since it often uses a different, smaller tile.

Metric example: 4.5 × 3.2 m with 12% waste and 1.44 m² cartons

1. Area: 4.5 × 3.2 = 14.4 m²
2. With 12% waste: 14.4 × 1.12 = 16.128 m²
3. Cartons: 16.128 ÷ 1.44 = 11.2
4. Round up: 12 cartons = 17.28 m²

Eleven cartons would give 15.84 m², which is below the 16.128 m² you need.

How many tiles per m²? Tiles per m² = 1 ÷ tile area in m². For a 300 × 600 mm tile, the area is 0.3 × 0.6 = 0.18 m², so 1 ÷ 0.18 = 5.56 tiles per m².

Tile size	Area	Tiles per m²
600 × 600 mm	0.36 m²	2.78
300 × 600 mm	0.18 m²	5.56
200 × 200 mm	0.04 m²	25
100 × 100 mm	0.01 m²	100

For a wall tile calculator in m², the steps are the same: wall area in m², plus waste, divided by carton coverage in m², rounded up.

Tile estimate mistakes that cause short orders

Using tile count instead of carton coverage

Counting tiles from nominal size and then guessing boxes often misses by a carton, as the 10 versus 12 example showed. Start from the carton coverage on the product page.

Forgetting the waste or applying it to the wrong number

Apply waste to the area, then divide. Adding 10% to the carton count (9.24 cartons + 10% = 10.2) is a different calculation and double-counts the rounding.

Mixing production lots

Ordering a few cartons now and a few later risks a visible shade change. Order the whole job at once and compare lot numbers on arrival.

Ignoring pattern, grout and layout

Herringbone, diagonal, large tiles in small rooms and out-of-square walls all raise waste. Check the room with the 3/4/5 method before ordering.

Pre-order checklist

1. Measured each dimension twice, in decimal feet or metres
2. Split L-shapes into rectangles and checked the total
3. Subtracted only large untiled areas
4. Chose waste for the layout (and checked with your installer)
5. Divided by the carton coverage printed on the product, not a tile count
6. Rounded up to whole cartons
7. Confirmed all cartons share one production lot
8. Decided whether to keep a spare carton for repairs

What about tile installation cost?

It varies by region, tile type and size, layout, and how much substrate prep the job needs, so any single figure would be a guess. Get two or three local quotes and ask what each includes: demolition and removal, underlayment or leveling, thinset, grout, trim and sealing. Comparing quotes line by line is more useful than comparing the totals.

For tile merchants: sell exact cartons instead of making shoppers do this math

Everything above is math your customer has to do before they can check out. If your store sells tile by the carton, every step is a chance for a wrong order.

Why per-variant pricing and quote forms fail

• A variant per room size: the catalog grows quickly, still misses the sizes people actually have, and the shopper still has to know how many cartons the room needs.
• "Enter square feet as the quantity": the product is sold in cartons, so a shopper who types 168 may buy 168 cartons or misread what the field means.
• Quote forms: a form delays the sale, and someone on your team has to do the math by hand. Manual fixes lead to wrong orders, returns and support tickets.

We walk through these in how to sell by square foot on Shopify.

How package rounding and cart quantity enforcement work

The fix is to put the calculation between the shopper's measurements and the Add to cart button. The shopper enters dimensions or an area. The tool converts units, applies your waste percentage, rounds up to whole cartons, and shows coverage and an estimated total. The measurements stay with the cart line, and the coverage updates if the shopper changes the quantity.

The Shoperize Price Calculator does this on Shopify. You configure unit conversion, waste, package coverage, rounding, limits and which products the rule applies to. You can build rules manually, start from a template, or generate an editable AI draft (plan limits apply). The Free plan supports one published area calculator on up to three products; advanced capabilities depend on the plan. Charges come from your Shopify catalog prices.

Example setup: 12 × 14 ft room, 10% waste, 20 sq ft carton

1. Rule inputs: area calculator in feet, 10% waste, 20 sq ft per carton, rounding up to whole cartons.
2. Shopper enters: 12 ft by 14 ft.
3. The app shows: 168 sq ft, 184.8 sq ft with waste, 10 cartons covering 200 sq ft.
4. Estimated total: 10 × your catalog price per carton. At a hypothetical $48 per carton, that is $480.
5. Cart: the quantity is 10, and the measurements travel with the line. If the shopper changes it to 11, the coverage shown becomes 220 sq ft.

What to configure and what to check

• Enter the carton coverage from your supplier's spec sheet, not a nominal tile size.
• Set the waste percentage per product or pattern, and decide whether shoppers can change it.
• Set minimum and maximum limits so a typo does not produce an absurd quantity.
• Test one product end to end: calculator, cart, checkout, and the order record your warehouse sees.

For deeper setup steps, see our guide to boxes, waste and cart setup for a square footage calculator, or try the Shopify tile calculator: area to cartons, with waste.

If you sell tile on Shopify, you can install Shoperize Price Calculator from the Shopify App Store (details at calculator.shoperize.com), and setup help is at help.shoperize.com.

Frequently Asked Questions

How do I figure out how much tile I need?

Multiply length by width to get the area, add waste (10% for a straight lay, 15% for diagonal), then divide by the coverage per carton. Round the result up to whole cartons. A 12 × 14 ft room at 10% waste with 20 sq ft cartons needs 10 cartons.

How much tile do I need per square foot?

It depends on tile size. Divide 1 by the area of one tile in square feet: 12 × 12 in tile is 1 per sq ft, 12 × 24 in is 0.5, and 6 × 6 in is 4. Then add your waste percentage on top.

How much extra tile should I buy?

Common rules of thumb are 10% for straight layouts, 10-12% for running bond, 15% for diagonal and 15-20% for herringbone or small, cut-heavy rooms. Your installer or the manufacturer may recommend a different figure, and a spare carton for future repairs is worth considering.

How do I do a tile estimate?

Measure the tiled surface twice, split L-shapes into rectangles, and subtract only large untiled areas. Add waste for your layout, divide by the carton coverage printed on the product, and round up. Check that all cartons come from one production lot.

How many tiles per m²?

Divide 1 by the area of one tile in square metres. A 300 × 600 mm tile is 0.18 m², so you need 1 ÷ 0.18 = 5.56 tiles per m², before waste. A 600 × 600 mm tile gives 2.78 per m².