Understanding your result
The headline is the number of boxes, with the area to tile, the pieces to order and the edge trim pieces beside it. The breakdown shows the gross backsplash area, the area removed by the window and the outlet boxes, the area to tile, and then the chain from pieces to boxes, with the trim at the end.
For individual tiles, the count uses the tile with its grout joint, exactly as on the wall tile calculator. For mosaic sheets the joint is already built into the sheet, so the sheet size is used directly; a 12 × 12 in sheet is one square foot. The waste allowance is 10% for a straight or brick layout and 20% for herringbone, and the reusable offcuts on a long straight run are the reason 10% is enough here when it might not be on a floor.
The edge trim rows are the piece of the shopping list most often forgotten. The top edge runs the full length of the counter unless cabinets hide it; each exposed end adds the backsplash height. Trim is counted in pieces of the length you entered, with 10% for the mitres at the corners. If you are using a metal profile sold by the 8 ft length, set the piece length to 96 in. The grout for a backsplash is small in quantity but matters for the look; the grout calculator takes the same tile size and joint.
How we calculate this
The outlet deduction uses the size of a single-gang electrical box, 2 × 4 in. A two-gang box is 4 × 4 in; enter it as two. The deduction is tiny in area and exists so that the figure is honest, not because it changes the order. What outlets really cost is cuts, and the note under the result reflects that when there are many. Waste comes from the layout table on the waste factors page. The guide to tile size and grout joints explains why small tiles and mosaics behave differently from large ones when you count them.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| Backsplash height | 18 in (45 cm) | The standard distance from counter to upper cabinets in US kitchens (KCMA and NKBA planning guidelines put it at 18 in; 15 to 20 in is the usual range) |
| Tile | 3 × 6 in subway, 1/16 in joint | The most common backsplash tile; manufacturers recommend 1/16 in for pressed subway tile |
| Mosaic sheet | 12 × 12 in, 10 sheets per box | Typical mesh-mounted mosaic packaging (manufacturer product pages, 2025) |
| Outlet box | 2 × 4 in (8 sq in) | NEMA single-gang device box dimensions |
| Edge trim pieces | 12 in | Pencil and bullnose trims are usually 12 in long; metal profiles come in 8 ft lengths |
| Waste | 10% straight, 20% herringbone | Tile manufacturer guidance; see the waste factors page |
Assumptions last reviewed October 7, 2026.
The calculator does not lay out the tile, so it cannot tell you whether a full tile fits under the cabinets or whether the end of the run finishes on a cut; for a 3 × 6 brick pattern it almost never matters, for a 12 × 24 it does. It does not count the thinset or the mastic, which for a backsplash is usually a small tub or one bag. And it treats the height as the same along the whole run; a tall section behind a range is a second run of the calculator. The large-format tile guide is the one to read if your backsplash uses 12 × 24 or longer tiles, where lippage shows under cabinet lighting.
Two worked examples
A 14 ft run of subway tile with five outlets
Height 18 in, no window, 3 × 6 in tile with a 1/16 in joint, straight brick pattern, 10 sq ft boxes at $25, one exposed end, 12 in pencil trim.
- Area: 14 × 18 ÷ 12 = 21 sq ft; less 5 boxes (0.3 sq ft) = 20.7 sq ft
- Pitch per tile: 6.0625 × 3.0625 ÷ 144 = 0.129 sq ft
- Tiles before waste: 20.7 ÷ 0.129 = 160.7; with 10%: 177 tiles
- Boxes: 80 tiles per box, 177 ÷ 80 = 2.2, rounded up to 3 boxes, $75
- Trim: 14 ft top edge + 1 end × 1.5 ft = 15.5 ft; 186 in ÷ 12 × 1.1 = 17.05, rounded up to 18 pieces
Three boxes is 240 tiles for a job that needs 177, which is the price of whole boxes on a small area. The 63 spare tiles are not a problem: subway tile is cheap, and a few kept back will repair a cracked one years later. The trim, at 18 pieces, often costs more than the third box.
A 9 ft run of mosaic sheets with a window
Height 20 in, a 4 sq ft window, three outlets, 12 × 12 in mesh sheets, 10 sheets per box at $42, two exposed ends, 12 in trim.
- Area: 9 × 20 ÷ 12 = 15 sq ft; less 4 sq ft window and 3 boxes (0.2 sq ft) = 10.8 sq ft
- Sheets before waste: 10.8 ÷ 1 = 10.8; with 10%: 11.9, rounded up to 12 sheets
- Boxes: 12 ÷ 10 = 1.2, rounded up to 2 boxes, $84
- Trim: 9 ft + 2 ends × 1.67 ft = 12.3 ft; 148 in ÷ 12 × 1.1 = 13.6, rounded up to 14 pieces
Two boxes leaves 8 spare sheets, which is a lot of mosaic. If the supplier sells single sheets, buy 12 or 13 and save half a box. The window takes more than a quarter of the area here, so the cuts around it are where the 10% is spent.
Where to find your inputs
Counter length. Measure along the back edge of the counter, every run that gets tile, and add them. Do not subtract the range or the sink; the tile runs behind both.
Height. From the counter surface to the underside of the upper cabinets, or to wherever the tile stops where there are no cabinets. Standard is 18 in; measure, because 17 and 19 are common.
Window. Width times height of the opening within the tiled band, including the casing. If the window sill is above the band, there is nothing to subtract.
Coverage per box. On the box and the product page. Subway tile is sold by piece count and square feet; mosaics by sheets per box, each sheet usually 1 sq ft.
Common mistakes
- Subtracting the range or the sink. The tile runs behind them. Only the window and the outlets come out.
- Forgetting the exposed end. Where the counter ends at a doorway, the tile edge shows and needs trim.
- Buying mosaic by the piece count. Mosaics come on sheets; count sheets and read the sheets-per-box figure.
- Using floor waste on a backsplash. A straight run of small tile reuses its offcuts; 10% is enough. Herringbone still needs 20%.
- Choosing the joint after buying the grout. Subway tile with 1/16 in joints takes unsanded grout; at 1/8 in it takes sanded. The joint decides the grout, not the other way round.
- Ignoring the outlet depth. Thick tile pushes the outlet face back; box extenders are a few dollars and avoid a loose outlet.
Questions people ask
- How many square feet is a typical kitchen backsplash?
- Multiply the counter length by the height to the upper cabinets. A 10 ft run at 18 inches is 15 sq ft; a kitchen with 20 ft of counter is 30 sq ft, less a window. Most kitchen backsplashes land between 15 and 40 sq ft, which is two to four boxes of tile.
- How much subway tile do I need for 15 square feet?
- A 3 × 6 inch tile with a 1/16 inch joint covers 0.129 sq ft, so 15 sq ft takes 116 tiles before waste and 128 with 10%. Boxes of 3 × 6 usually hold 80 pieces (10 sq ft), so you buy 2 boxes and have 32 tiles over.
- How many mosaic sheets do I need?
- Most mosaics are mounted on 12 × 12 inch mesh sheets that cover 1 sq ft each, sold 10 to a box. A 12 sq ft backsplash needs 12 sheets plus 10%, which is 14 sheets and 2 boxes. Sheets cut at the end of one row are usually reused at the start of the next, so 10% is enough for a straight layout.
- Do outlets change how much tile I need?
- Barely for the area. A single-gang box is 2 × 4 inches, about 0.06 sq ft, so even eight outlets remove half a square foot. They matter for the cuts, since each box is two to four notched tiles that are easy to break, and for the box extenders you may need if the tile is thick. The calculator subtracts the area and warns when there are many.
- What edge trim does a backsplash need?
- The top edge where the tile meets the wall above the counter, unless the upper cabinets cover it, and any vertical end that does not stop at a wall or cabinet. Options are a pencil or bullnose tile in the same line, a metal profile, or for some tiles a finished edge. Trim is usually sold in 12 inch pieces; the calculator adds 10% for the mitres.
- Should the backsplash height include the area behind the range?
- If the tile runs up to a hood, that section is taller, often 30 inches or more. Enter the taller height if most of the run is tall, or run the calculator twice, once for the 18 inch run and once for the tall section, and add the pieces. The second method is more accurate.