What If I Don't Know the Final Layout Yet?

Waste percentage isn't a property of the room, it's a property of the pattern. The same 120 sq ft bathroom floor can need as little as 7% extra tile in a straight-set grid or as much as 20% extra in a diagonal or herringbone layout, according to the National Tile Contractors Association Reference Manual. If you haven't picked the pattern yet, you don't actually know which number applies to your job — so the only safe move is to order for the higher end of the range you're realistically considering, not the lower end you're hoping to land on.

15% is the number to use as a default when the layout is genuinely open. It covers a standard running-bond or grid layout with room to spare, and it gets you close enough to a diagonal or basketweave pattern that you won't be stuck ordering a second, possibly mismatched batch. It is not a substitute for running the actual calculation once you commit — it's a placeholder that keeps you from under-buying while you're still deciding between options in the /tile-estimator or looking at options on the /patterns page.

A straight-set grid cuts tile only where it meets a wall or fixture, which is why the TCNA Handbook allows as little as 7% overage for that layout. Every other pattern adds cuts that a grid doesn't have. A 45-degree diagonal doubles the number of edge pieces because every border tile gets a mitered cut instead of a straight one. Herringbone and basketweave add cuts on both ends of every field tile, not just the perimeter, which is why those patterns sit at the 15-20% end of the NTCA's recommended range.

Tile format matters too, but less than pattern does. Large-format rectangular tile laid in a simple grid still lands near the 7-10% baseline. The same large-format tile laid on the diagonal or in a herringbone jumps toward 20% because the offcuts from each cut piece are too small to reuse anywhere else in the layout. If you're weighing a herringbone backsplash or floor, run it through the /guides/herringbone-tile-layout-calculator once you're seriously considering it — the jump in waste is large enough that it changes how many boxes you need to buy, not just how many tiles.

Ordering for a 10% straight-set layout and then switching to herringbone mid-project is the most common way installers run short mid-job. The shortfall doesn't show up until the crew is most of the way through the field tile, at which point the border and cut pieces are what's left — exactly the tiles the higher waste factor was supposed to cover.

The bigger problem isn't the shortage itself, it's what happens when you go back to order more. Tile is manufactured in dye lots, and a reorder placed weeks after the original purchase can come from a different lot with a visible shade or size variation, especially in natural stone or handmade-look ceramic. Manufacturers can also discontinue a run entirely between the original purchase and the reorder, which turns a small shortfall into a full re-tile. Ordering the extra 15% up front costs less than any of those outcomes, and unopened boxes are generally returnable if you end up not needing them — check the retailer's return window before you assume you're stuck with the overage.

The 15% placeholder exists to get you through the buying decision, not to replace the actual calculation. Once the pattern is set, re-run the numbers with the real layout selected in the /floor-tile-calculator or /wall-tile-calculator so the waste factor matches the pattern instead of a generic guess. If the final call is a straight grid, you may be able to trim the order back toward 10%; if it lands on diagonal or a mixed layout, you'll want to confirm you're not still short of the 20% mark.

Box rounding happens after the waste factor, not before it. Once you have the tile count for the actual pattern, round up to the next full box — partial boxes aren't sold, and the last few tiles of coverage almost always land inside a box you already need to buy. Run that final pass through the /tile-estimator so the box count reflects the pattern you actually installed, not the placeholder you started with.