When laying floor tiles, what size will give the best illusion of space?

Well - until a sensible answer turns up - about 12 parsecs...

Geo

The size of the tile is less important that the size and stridency of the pattern.

Consider a tile with a pattern on it, the pattern is in black and white, this makes it strident, and how often the design repeats is more apparent to the eye, and this sets the eye's natural measuring process in train.

Now consider the same size of tile with the same design, but in say cream and a pale sand; since the colours are a closer match to each other tonally, then this disguises the stridency we noted before, and so fools the eyes enough to stop or at least severely postpone any natural sizing up routines.

You can see from this that the scale of the design now plays a smaller role than you may have imagined before. It follows that the size of the tiles will also follow that set of rules too, to a greater or lesser extent, depending on each design and colour choice combination. Also the colour of grout can have a bearing too, and for the same reasons.

These are not hard and fast rules, but it can become a helpful guide if practiced enough, as it works for walls and wallpaper, and even soft furnishing fabrics - probably for furniture design and wood choice therein too for all I know.

Take Care, Gnube {too thick for linux}