It is best to make medium -length seams.

It is not necessary to determine the width by eye, you can use special crossings for tiles. They are of various sizes, which determines the width of the seam. If you lay the tile tightly, then the seam will be less than 3 mm, in this case, the grout will not be able to get inside. If you make a seam of more than 12 mm, then the grout will fit easily, but after drying there is a high probability that it will crack, and the appearance will be spoiled. It is best to make medium -length seams. So, for large tiles, seams about 6 mm are suitable, and for smaller tiles — from 3 to 4 mm. A mixture of epoxy resin should be used if the seam is no more than 6 mm.