Use thin grout lines of 1/8 or 1/16 of an inch when installing tiles measuring 16-by-16 inches, 20-by-20 inches or larger. Use non-sanded grout for grout lines measuring 1/16 of an inch and sanded grout for 1/8 of an inch lines. Do not omit the grout in an attempt to create a "seamless" floor. Tiles are not exactly the same size; several 20-by-20 inch tiles will vary in size by as much as 1/4 of an inch in overall height and width. Grout lines are necessary to maintain consistency. If you butt tiles together without grout lines, the result is uneven seaming and after some time, you may see gaps between tiles due to tile movement.
Create grout lines measuring 3/16, 1/4, 3/8 or 1/2 of an inch for tiles measuring 12-by-12 inches or for slightly smaller tiles such as 8-by-8 inch or rectangular-shaped tiles. Wider grout lines are more noticeable and thus more influential on the final aesthetic effect of the tile installation. Use the smaller-sized lines if you want the grout to blend into the background. If the grid effect is complementary to your design scheme, use larger grout lines.
Meshed tile squares, measuring 12-by-12 inches, are made up of 1-by-1 inch tiles held together with a mesh backing. Once you install a square of tiles, you apply the grout. The space surrounding each 1-inch square on the tiles, typically measuring approximately 3/16 of an inch, determines the size of the grout line. Allow for 1/8 inch or 1/16 inch grout lines if you use smaller tiles in your project, such as 4-by-4 inch tiles so the tiles don't appear to "float" amid a sea of grout.
Use a grout in a contrasting color and create wider lines if you wish to use the lines in the design. This is particularly effective with 12-by-12 inch tiles. For example, black tiles mixed with a pure white color grout create high contrast. Other color combinations include dark brown tiles with red grout, white tiles with red or dark gray grout and red tiles with black or white grout. You can use a 1-inch grout line for this type of design to emphasis the resulting grid pattern in the design scheme.