The backsplash measurement method
A backsplash is a rectangle: the length of countertop run times the height from counter to cabinet. Measure the run in inches along the wall, multiply by the height in inches, and divide by 144. That is the tiled area. Convert to tiles by dividing the area by the coverage of one tile (tile length times tile width in inches, divided by 144), then add the waste factor.
The standard height is 18 inches, the gap between a 36 inch countertop and cabinets hung at 54 inches. If the backsplash runs behind the range, measure that section separately at its full height, usually 30 to 36 inches from cooktop to hood. If the backsplash goes full height to the ceiling, use the true height instead of 18 inches.
Do not subtract outlets, switches, or the range cutout from the area. Each cutout saves a fraction of a square foot but forces a cut that often breaks a tile, so the savings are imaginary. The 10 percent waste allowance covers every outlet in a normal kitchen.
Worked example: a 10 foot run of subway tile
Take a straight 10 foot countertop run at the standard 18 inch height. Area: 120 inches times 18 inches is 2,160 square inches, divided by 144 gives 15.0 square feet. A 3 by 6 inch subway tile covers 18 square inches, which is 0.125 square feet. Divide: 15.0 divided by 0.125 is exactly 120 tiles. Add 10 percent for cuts: 120 times 1.10 is 132 tiles.
Box math: if subway tile comes 50 to a box, 132 divided by 50 is 2.64, so buy 3 boxes. Those 3 boxes hold 150 tiles, which gives you 18 spares beyond the order, a comfortable cushion for a first-timer's cuts. Run your own numbers in the tile calculator by entering the backsplash area as the room size.
Worked example: an L-shaped kitchen
Most kitchens have two runs. Say one run is 8 feet and the other is 6 feet, both at 18 inches high. Measure each rectangle: 96 times 18 is 1,728 square inches, or 12.0 square feet; 72 times 18 is 1,296 square inches, or 9.0 square feet. Total: 21.0 square feet. With 3 by 6 subway tile: 21.0 divided by 0.125 is 168 tiles, times 1.10 is 184.8, so buy 185 tiles.
The corner where the two runs meet deserves care in layout, not in math. Plan the corner so a full tile lands on the visible side and the cut tile hides in the corner. The area math does not change: corners cost layout time, not extra tile, as long as you keep the 10 percent.
Herringbone and patterned backsplashes: use 20 percent
Backsplashes are where herringbone shows up most, and herringbone doubles the cutting. Every tile that meets the edge of the pattern gets cut at 45 degrees, and those offcuts rarely fit anywhere else. Use a 20 percent allowance instead of 10. The 10 foot run from the first example: 120 tiles times 1.20 is 144 tiles.
The same 20 percent applies to chevron, double herringbone, and any pattern laid on the diagonal. The pattern looks expensive precisely because it wastes tile, so budget for it honestly rather than discovering it mid-job.
Tile size changes the box count, not the method
Large format tile on a backsplash means fewer pieces and fewer grout lines. The same 15 square foot run with 12 by 24 inch tile (2 square feet each): 15.0 divided by 2 is 7.5, times 1.10 is 8.25, so buy 9 tiles. Fewer tiles, but each cut matters more, because one broken 12 by 24 is two square feet of the order. Keep the 10 percent even though the tile count is small.
Mosaic sheets flip the other way: a 15 square foot backsplash at 1 square foot per sheet is 15 sheets times 1.10, which is 16.5, so 17 sheets. Sheets cut easily and waste little, but count the sheets, not the individual mosaic chips. Once you have the tile count, size your grout with the joint formula in our grout guide, since small tile eats grout.