What size grout line for tile?
1/16 in for rectified and subway tile, 1/8 in for standard floor tile, 3/16 in for large format.
The tile decides this more than you do. A joint has to be wide enough to absorb how much the tiles themselves vary in size — push it narrower and every difference shows as a crooked line.
Joint width by tile
| Tile | Joint | Grout type |
|---|---|---|
| Mosaic (1x1, 2x2) | 1/16 in | unsanded |
| Subway 3x6 | 1/16 in | unsanded |
| 4x4 | 1/16 in | unsanded |
| 6x6 | 1/8 in | sanded |
| 8x8 | 1/8 in | sanded |
| 12x12 | 1/8 in | sanded |
| 12x24 | 3/16 in | sanded |
| 18x18 | 1/8 in | sanded |
| 24x24 | 3/16 in | sanded |
| 24x48 | 3/16 in | sanded |
The sanded/unsanded split falls at 1/8 in. Sanded grout will not pack into a narrower joint; unsanded grout in a wider one shrinks as it dries and cracks along the middle of the line.
Why the tile sets the minimum
Tiles are not all the same size. Pressed tile varies by up to about 1.5% along an edge, which on a 12 in tile is nearly 3/16 in between the smallest and largest in the box. A joint has to be wide enough to swallow that variation and still look straight.
Rectified tile has been ground square after firing, so the variation is a fraction of a millimetre and 1/16 in joints are achievable. Tile that is not rectified cannot hold a 1/16 in line, and forcing it produces joints that wander visibly from one course to the next.
The other constraint is the long edge. Large-format tiles are often slightly bowed, so a running-bond layout offsets the crown of one tile against the dip of its neighbour and lips. That is why the guidance for 12x24 is a 3/16 in joint and an offset of no more than a third rather than a half.
Common questions
- What size grout line for 12x24 tile?
- 3/16 in, with a one-third offset rather than a half. Both exist to manage the same problem: the slight bow along a 24 in edge, which a wider joint absorbs and a narrow one puts on display.
- What size grout line for subway tile?
- 1/16 in is traditional and what most subway tile is made for. Some looks want 1/8 in, which is fine — just move to sanded grout at that point.
- What size grout line for 12x12 floor tile?
- 1/8 in for a standard pressed tile, 1/16 in only if it is rectified. This is the most common floor joint there is, and it is why 1/8 in spacers are the ones that always sell out.
- What size spacers should I use?
- Spacers match the joint: 1/16, 1/8 or 3/16 in. Buy more than you think — roughly four per tile if you are using them at the corners, so a 100 sq ft floor of 12x12 tile wants about 400.
- Can I use a narrower joint to make it look modern?
- Only with rectified tile. The narrow-joint look comes from the tile being ground square, not from the spacers. Trying it with standard tile is the single most common way a floor ends up looking amateur despite being flat.
- Does a wider joint need more grout?
- Considerably. Going from 1/8 in to 3/16 in on 12x12 tile raises grout from 17.2 lb per 100 sq ft to 25.8 lb — half as much again.
Related answers
Or work out the area first with the tile calculator.