Tile size changes a room more than tile colour does. The same warm grey looks calm in a large format and busy in a small one. Choosing the size is a design decision and a practical one at the same time, and it is easier than it looks once you work through it in order.
Here is a step by step method that gives you a confident answer for any room.
Step 1: measure the room and note the shape
Write down the length and width and look at the proportion. A long narrow room, a small square room and a large open room each want something different.
Also note the ceiling height, because it decides whether you can use a large format vertically on the walls without awkward cuts.
Step 2: start bigger than instinct suggests
The common assumption is that small rooms need small tiles. In practice the opposite usually works better. Fewer grout lines let the eye read one continuous surface, which makes a space feel larger and calmer. A 600 by 600 or a 600 by 1200 in a small bathroom generally looks more generous than a 300 by 300.
The exception is where a floor has to fall toward a drain, since a large rigid tile cannot follow a curved surface. That is where small formats and mosaics earn their place.
Step 3: match the format to the room proportion
Rectangular tiles have direction, and you can use it. Laid with the long edge across a narrow room, they widen it. Laid vertically on a wall, they lift the ceiling. A square tile is neutral and calms a room that already has a strong shape.
In a long corridor, running planks along the length emphasises the length. Running them across it shortens the room visually. Decide which effect you want before ordering.
Step 4: check the setting out
This is the step that separates a good tiling job from an ordinary one. Sketch the room to scale and lay the tile size onto it. You are looking for where the cuts land.
Whole tiles should sit where the eye goes first, which is usually the doorway view and the main wall. Cut tiles should be pushed to the corners, under fittings, or to the least visible edge. If a size leaves a thin sliver of tile at a prominent edge, either shift the starting point or change the size.
A sliver narrower than about a third of a tile always looks like a mistake, so it is worth adjusting to avoid one.
Step 5: consider the substrate
Large tiles need a flat surface. A floor or wall with more than a few millimetres of variation will cause lipping, where one edge sits proud of the next, and on a large format that is very visible.
If the substrate is uneven and cannot be levelled, a smaller format is the practical answer. Ask your installer for an honest view before choosing, since they are the ones who will have to make it look right.
Step 6: think about grout and cleaning
Every grout line is a line to clean. In a commercial kitchen, a shower, or any room that is washed daily, fewer joints means less work and fewer places for dirt to sit.
Rectified tiles, which are cut to exact size after firing, allow a 2mm joint instead of 3 or 4mm, sharpening the whole effect. Ask whether the range you like is available rectified.
Step 7: order the right quantity
Add 10 percent for straight layouts and around 15 percent for diagonal or herringbone patterns, since angled cuts create more waste. Keep the spare boxes from the same batch, because shade varies slightly between production runs and a matching tile in three years is worth having.
Quick answers by room
Small bathroom: 600 by 1200 on the walls, matching floor, mosaic only in the shower base or the niche. Large open living space: 800 by 800 or a slab format, laid with a minimal joint. Corridor: planks running across the width to shorten it visually, or along it to emphasise length. Commercial kitchen: smaller textured format with a high slip rating and an epoxy grout. Pool surround: small format or hexagons for grip and for following the fall to the drain.
Work through those seven steps and the size chooses itself. If you would like help matching a format to real production for a project, our team in Foshan works with these ranges every day.