When laying tiles, you can use spacers to ensure you maintain a gap of consistent size. These are small devices, made of rigid plastic, shaped like a plus sign. Their four “limbs,”enable them to sit between the corners of four tiles, spacing them out equidistantly.
The Tile Association advice
There are several different sizes of spacer available, from 2 mm (0.08 inches) to 6 mm (0.24 inches). According to The Tile Association, the smallest gap you should allow between tiles is 2 mm (0.08 inches). If you are aiming for this size of gap, buy 2 mm (0.08 inch) spacers. For floor tiles, 3 mm (0.12 inches) is the smallest gap. Although some people leave the spacers in place, The Tile Association has contrary advice. They suggest you insert the spacers at right angles to the tile, to facilitate removal.
Spacers dictate the amount of space between tiles but you fill this space with grout in due course. A 5 mm (0.2 inch) gap between tiles -- as created by 5 mm (0.2 inch) spacers -- will obviously require more grout than a 2 mm gap (0.08 inches). If you are happy with a wider grout line -- and you are sure the look is right for the job -- choose larger spacers, and vice versa.
Carry a ruler
In the run-up period to a tiling job, you might want to carry a 15 cm (6 inch) ruler in your pocket. Whip it out whenever you are in a tiled room whose grouting width you like. Measure the grouting width in millimetres to establish the size of spacer you need. It might be prudent to do this when nobody else is in the room, to save having to explain what you are up to.
Topps Tiles favour 2 mm (0.08 inches) spacers for tiling jobs on the walls of bathrooms and kitchens. They suggest 5 mm (0.2 inch) spacers when laying floor tiles. In terms of their effectiveness, it’s immaterial what size of spacer you use, so long as you use the same size spacers for each job.