Tile Spacer Size Guide

Joint width by tile type

The rule that actually sets the joint: three times the size variation

The chart above is a starting point. The tile itself decides. The installation standard most US tile is installed to (ANSI A108.02) says the grout joint must be at least three times the actual variation in the tile's facial dimensions, and never less than 1/16 in. A tile that varies by 1/32 in from piece to piece needs at least a 3/32 in joint, which in practice means a 1/8 in spacer.

Measure it yourself before you buy spacers. Take ten tiles from at least three different boxes. Measure the same edge on each with a steel rule or calipers, and write the numbers down. The largest minus the smallest is the variation. Rectified porcelain often comes in under 1/64 in; pressed ceramic and handmade tile can vary by 1/16 in or more.

Joint width changes the last cut, not just the look

Each joint adds to the run, so the spacer you choose moves where the last tile lands. On large tile it hardly shows. On small tile it adds up fast. Here is a 96 in (8 ft) backsplash in 3x6 subway laid on its long side, starting with a full tile at one end:

Going from 1/16 in to 1/4 in eats over two inches of the run and shrinks the end cut from about five inches to a sliver of about two. Decide the joint width first, then plan the layout. Doing it the other way round is how backsplashes end up with a thin strip beside the window trim.

Metric and inch spacers are not the same size

Many spacers are made in millimetres and sold with inch labels. A 3 mm spacer is 0.118 in; a true 1/8 in is 3.175 mm. The 0.175 mm difference is invisible in one joint but adds up across a room:

Use one bag, or one brand, of spacers for a whole floor. When you are matching an existing floor or wall, measure an old joint with a feeler gauge or drill bits rather than trusting the label on a new bag.

Which kind of spacer for which job

Common spacer mistakes

• Grouting over spacers left flat in the joint. The grout over them is a fraction of full depth. It cracks, dries a different shade and shows the shape of the spacer. Pull them once the thinset has firmed up.
• Choosing 1/16 in because it looks modern, on tile that is not rectified. The joints wander and the corners lip. The three-times rule above is the check.
• Spacing tile tight to the walls. The perimeter needs a movement gap, normally about 1/4 in, hidden under the baseboard or filled with caulk. A spacer against the wall leaves no room for the floor to move.
• Adding spacers to self-spacing tile. Some wall tile has small lugs on the edges that set the joint. Spacers on top of the lugs double the joint.
• Spacing mosaic sheets by eye. The joints between sheets must match the joints inside each sheet, or the sheet outlines show from across the room. Use a spacer the same width as the sheet's own joint between sheets.