How Much Tile Do I Need? Herringbone vs Straight Lay

The short answer

Measure the floor, add a waste allowance for the layout, then divide by the area one tile covers including its grout joint. A straight lay usually starts at 10% extra and herringbone at 20%. Those are installer and retailer conventions, not a published standard, so treat them as a starting point and go higher for small rooms, long planks or lots of corners.

In practice, herringbone often costs one extra box in a small bathroom and several in a big room. The rest of this guide shows why herringbone wastes more, works through a bathroom in two plank sizes, and covers the rounding and spares that catch people out.

Why herringbone wastes more tile

In a straight or offset lay, tiles only get cut where the floor meets a wall. Most offcuts from one end of a row can start the next row, so little is thrown away.

Herringbone is different:

• Every edge tile is cut at an angle. The zigzag meets each wall at 45 degrees, so the last tile in every row needs an angled cut.
• Offcuts rarely fit elsewhere. An angled offcut from one wall is usually the wrong shape, length or direction for the next gap.
• Long planks lose more per cut. A 24 inch plank cut at 45 degrees near a wall can lose most of its length.
• Small rooms are worst. A bathroom has a lot of wall edge for its floor area, plus a toilet flange and a vanity to cut around, so the share of cut tiles is high.

That is why the waste allowance climbs from about 10% for a straight lay to 15% for a diagonal lay and 20% for herringbone. No tile maker or the tile industry handbook publishes one waste figure, because it depends on the room, the tile size and the installer. Your installer’s number beats any table.

Layout	Starting waste allowance	Where the waste comes from
Straight (grid or offset)	10%	Cuts along the walls only
Diagonal (45°)	15%	Angled cuts at every wall
Herringbone	20%	Angled cuts at every wall, short offcuts that rarely reuse

The formula

1. Area: length × width of each part of the floor, added up.
2. Add waste: area × (1 + waste %). For herringbone, area × 1.20.
3. Area per tile, with joint: (tile length + joint) × (tile width + joint) ÷ 144, in square feet, with sizes in inches.
4. Tiles: step 2 ÷ step 3, rounded up.
5. Boxes: tiles ÷ tiles per box, rounded up.

Including the grout joint in step 3 matters more for small tiles. A 3 × 12 inch tile with a ⅛ inch joint covers 3.125 × 12.125 = 37.9 square inches, about 5% more than the tile’s own 36 square inches.

Worked example: an 8 × 10 ft bathroom floor

The floor is 80 square feet. The grout joint is ⅛ inch. Two plank sizes are on the shortlist. The box counts below are example carton sizes chosen to make the arithmetic easy to follow: 40 pieces of 3 × 12 or 15 pieces of 4 × 24 (both 10 square feet a box). Read the actual count on the carton you are buying.

3 × 12 inch plank. Each tile with its joint covers 3.125 × 12.125 ÷ 144 = 0.2631 square feet.

• With no waste: 80 ÷ 0.2631 = 304.1, so 305 tiles.
• Straight lay, 10%: 88 ÷ 0.2631 = 334.5, so 335 tiles, 9 boxes (360 tiles, 25 spare).
• Herringbone, 20%: 96 ÷ 0.2631 = 364.9, so 365 tiles, 10 boxes (400 tiles, 35 spare).

4 × 24 inch plank. Each tile with its joint covers 4.125 × 24.125 ÷ 144 = 0.6911 square feet.

• With no waste: 80 ÷ 0.6911 = 115.8, so 116 tiles.
• Straight lay, 10%: 88 ÷ 0.6911 = 127.3, so 128 tiles, 9 boxes (135 tiles, 7 spare).
• Herringbone, 20%: 96 ÷ 0.6911 = 138.9, so 139 tiles, 10 boxes (150 tiles, 11 spare).

Tile	Layout	Tiles needed	Boxes	Spare tiles
3 × 12 in	Straight, 10%	335	9	25
3 × 12 in	Herringbone, 20%	365	10	35
4 × 24 in	Straight, 10%	128	9	7
4 × 24 in	Herringbone, 20%	139	10	11

In this bathroom, herringbone costs one more box in either size. Notice how thin the spare count is for the 4 × 24 straight lay: 7 tiles. With long planks, two bad cuts or one cracked tile can use that up. If you are laying long planks in herringbone in a small room, many installers would push the allowance past 20%, and the tile calculator lets you type in any percentage.

Plank tile has its own rules

Long rectangular tiles are rarely perfectly flat along their length. The Ceramic Tile Education Foundation notes that wood-look planks are large format and subject to inherent warpage, and that this bow causes lippage (one tile edge sitting higher than the next) when planks are offset by half their length.

For that reason, ANSI A108.02 limits running-bond offsets on long tiles to a maximum of 33% unless the tile maker specifies otherwise. CTEF articles quote the size threshold as a side longer than 18 inches in one place and 15 inches in another, so check the edition your installer works to. Either way, a 24 inch plank is covered. An offset larger than 33% needs the owner to approve a mock-up and the lippage that comes with it.

Two knock-on effects for buying:

• Offset and waste are linked. A ⅓ offset pattern produces different offcuts from a ½ offset. Ask your installer which pattern they will use before you settle on the waste figure.
• Joint width changes the count. In running bond with long tiles (a side over 15 or 18 inches, depending on the source), the minimum average grout joint is ⅛ inch for rectified tile and 3/16 inch for calibrated tile, increased by the amount of edge warpage. A wider joint means slightly fewer tiles per square foot, so enter the joint your installer plans to use.

The International Masonry Institute reports that the ANSI A108 committee found the running-bond wording too narrow and formed an ad hoc subcommittee on offset bonding to write broader language. IMI points out that herringbone and basketweave can line a tile’s corner up with the middle of its neighbor, the same setup that causes lippage in running bond. Until new wording is approved, follow the tile maker’s installation sheet for herringbone with long planks.

Buy enough from one batch

Fired tile varies from batch to batch. Daltile rates its products for shade variation from V0 (uniform) to V4 (considerable variation from tile to tile). Two practical habits follow:

• Buy the whole job, plus spares, at once. A box bought months later may not match.
• Blend as you go. On higher-variation tile, pull from several boxes as you set so no patch of floor looks different from the rest.

Keep the spare tiles. A cracked tile in five years is a one-tile repair if you still have matching stock, and a whole-floor problem if you do not.

Common mistakes

• Using the herringbone allowance on the whole house. If only the entry is herringbone and the rest is straight, work them out as separate areas with their own waste.
• Leaving out the grout joint. Dividing by the bare tile size overestimates the tiles you need, slightly for large tiles and more for small ones.
• Forgetting the box rounding. You cannot buy 0.4 of a box. The real overage is your waste allowance plus whatever is left in the last box.
• Comparing square feet per box between tile sizes. Two products with the same square feet per box can need different box counts once joints and waste are included.
• Not counting trim and transitions. Bullnose, edge trim, thresholds and transition strips are separate items.
• Planning herringbone without a layout. Herringbone is usually centered on the room or the doorway. A layout dry-fit tells you where the worst cuts land before you buy.

When to call a pro

• Long planks or large format tile on an uneven floor. Flatness requirements for large tiles are tight, and lippage is hard to fix after the grout cures. An installer can check the subfloor and plan the offset.
• Herringbone in a room with several doorways. Keeping the pattern centered and continuous through openings takes careful layout.
• Heated floors, showers and wet areas. Waterproofing, slopes and heating mats are where most failed bathroom floors start.
• Anything over a wood subfloor that flexes. Deflection limits for tile are strict. If the floor bounces, ask a contractor before you buy tile.

To run the numbers for your own rooms, including several areas, the waste for each layout, boxes and grout, use the tile calculator.