Grout joint width is a choice, not one required size
ANSI A108.02 section 4.3.8 says the nominal centerline of joints should be straight and of even width, with allowance for hand-molded or rustic tile. The Tile Council grout FAQ says that is the standard's joint-spacing language, and it does not pick one width.
What should drive the choice
Tile-to-tile size variation, irregular edges, tile size, a surface that scratches easily, the location, and whether the plane is level all matter. The project owner chooses the joint, knowing a tighter joint shows more variation. Many people find that a joint smaller than three times the average tile-to-tile variation, or two times the maximum variation, looks irregular. Over a hump the joint opens. Across a low spot the top of the joint narrows.
Sanded or unsanded
For cement grout, joints smaller than 1/8 inch generally take unsanded grout. Joints of 1/8 inch and larger take sanded grout. Joints larger than 3/8 inch usually need a more heavily sanded mix. Sanded and unsanded grout should not be mixed.
Source
Fetched 2026-10-11 from Tile Council grout FAQ. The sentences above follow that page. They are not a contractor promise.
Related notes
- Tile notes index
- Movement joints relieve stress between tile and its substrate
- Blotchy grout color is usually a mixing or washing problem
- Shower photos
Send photos if you want another person to look at the area. This note does not set a response time.