How to use this calculator
Enter each wall you are tiling as a separate run, in feet, then the height of the tiled area in inches. A kitchen backsplash is 18 inches; a shower surround is usually 72 to 96; a full bathroom wainscot is 48.
Pick the offset that matches what you want to see, then the joint width. A 3 by 6 tile at a 1/16 inch joint and the same tile at a 1/4 inch joint are different products visually and different orders on the grout line.
Offset choices and their waste
Four offsets cover almost everything people build. The choice moves the waste allowance between 10% and 17%, and the difficulty by a lot more.
| Offset | Waste | Best for |
|---|---|---|
| Half (running bond) | 10% | Classic look, tile up to 12 in long |
| Third | 12% | The ANSI A108.02 limit on tile over 15 in; hides lippage |
| Vertical stack | 10% | Modern, least waste, needs plumb walls |
| Herringbone | 17% | Feature walls, double the labour |
A half offset on a long tile is the one genuine mistake in that list. Long tiles have some inherent warpage; at a half offset the high edge of one tile sits against the low edge of the next and you get lippage you cannot trowel out. The installation standard, ANSI A108.02, sets a maximum offset of 33% where the side being offset is longer than 15 inches, unless the manufacturer specifies otherwise. The reasoning across all patterns is set out in tile waste factor by pattern.
Where you start the first course decides how the offsets land. On a backsplash, centre the field on the range or the sink rather than on the wall, because that is the line people look at. On a shower wall, start from the corner that is most visible when the door opens and push the cut tiles into the far corner. Either way, dry-lay one full course along a straightedge first: a 10 foot run of 3 by 6 tile is 20 tiles, and a 1/32 inch error repeated 20 times is over half an inch of drift by the end of the wall.
Grout joint width matters more than you think
A 3 by 6 tile has about 6 linear feet of grout joint in every square foot of wall, four times the 1.5 feet in a square foot of 12 by 24. That is why small tile uses so much grout. Working from Custom Building Products’ coverage charts, the calculator puts a 3 by 6 at 0.14 pounds per square foot at a 1/8 inch joint, against 0.05 for a 12 by 24.
Double the joint and you roughly double the grout. Going from 1/16 to 1/4 inch on a 60 square foot backsplash of 3 by 6 takes the calculator from about 4.1 pounds of non-sanded grout, one 10 pound box, to 15.6 pounds of sanded, one 25 pound bag. It also changes the look completely: a tight joint reads as a continuous surface, a wide joint reads as a grid of individual tiles.
Handmade or "zellige" tile has irregular edges and cannot be laid tight; give it 3/16 inch or more. Rectified tile allows a tighter joint than calibrated tile, but for offset patterns with tile longer than 15 inches ANSI A108.02 sets an average minimum of 1/8 inch for rectified tile and 3/16 inch for calibrated, widened by the tile’s edge warpage.
One quantity that never appears in the square footage: the spacers. A 60 square foot backsplash in 3 by 6 tile has roughly 480 tiles and needs about 1,000 spacers, because every tile takes two. They come in bags of 100 to 500 and they are the item people run out of at nine on a Saturday night. Buy twice what you think, and buy the horseshoe type rather than the cross type so you can pull them after the thinset has grabbed.
Common mistakes
- Not counting the returns. The 4 inch strip beside a window and the 3 inch return at the end of a run are full cuts and they are easy to leave off the order.
- Starting a shower wall at the pan. Pans slope. Start from a level ledger board one full tile up, tile the field, then come back and cut the bottom row to the slope.
- Assuming 3 by 6 is 3 by 6. Nominal sizes are not actual sizes: a tile sold as 3 by 6 may measure a fraction under it, with the joint making up the rest. Check the actual size on the box before you plan the cuts at the end of each run.
- Buying bullnose at the end. Finished-edge pieces come from the same dye lot as the field tile and sell out first. Order them together.
- Grouting the corners. Treat inside corners and the joint at the pan as movement joints and fill them with a flexible sealant, not grout; grout there tends to crack.
- Tiling over drywall in a shower. The waterproofing that goes behind the tile is covered in the shower tile planning guide, and it is not optional.