Spacer size - rule of thumb? Equation? Please advise

[j_v_z]

After searching through, and for, threads about spacer size, I've come up with nothing really definitive.

I have seen people recommend 3x the variation in tile size, but What does this mean? if i am installing a 12x24" tile, the variation is 1:2 correct? now 3x that is what? and what are the units of measure?

Please advise. thanks!

[cx]

Zoe, the variation in question there is the difference between the largest and smallest tile in your layout, measuring the same dimension on each tile, of course.

Get a large handful of tiles from different boxes and stand them on edge. Put a straight edge across the top edges and see how much difference you have. Multiply that difference by three to get the industry recommended grout joint width.

If you have 1/16th-inch difference between the largest and smallest, your smallest recommended grout joint would be 3/16th of an inch.

[Platypus]

Agree with CX, except for one thing. Do this with ALL of your tiles. I made the mistake of using a "representative sample" of about 1/3 to 1/2 of my tiles and that was not enough. The very biggest ones made it past that test and I had a couple of them already up before I realized what had happened. Threw off the whole layout on one wall.

You could find the smallest and largest tile from each box, then compare all of these extremes from each box against the extremes of the other boxes. That way you won't have to stack up all the tiles at once.

And remember to do this in both dimensions, like cx said.

Don't make assumptions that the boxes will match each other. I did, and it cost me. Also remember that 3X the variation is the bare minimum. If I had to do it over again, I would go with 4 X variation.