Grout line width depends on the tile type and look you want. This chart gives the typical spacing (and so the spacer size) for common tiles.
| Tile type | Typical grout line |
|---|---|
| Mosaic | 1/16 in |
| Glazed wall tile | 1/16 – 1/8 in |
| Rectified porcelain | 1/16 – 1/8 in |
| Standard floor tile | 1/8 – 3/16 in |
| Natural stone | 1/8 – 1/4 in |
| Tumbled / rustic | 1/4 in or more |
Rectified tiles go tight. Their precisely cut edges allow narrow joints; non-rectified tiles need wider grout lines to absorb slight size differences. Stay at 1/16 in minimum.
See the How to Install Tile guide and the Tile Calculator.