How many tiles do I need?
Divide the area to cover by the area of one tile, then add waste. A 3 by 4 metre floor is 12 square metres; with 300 by 300 mm tiles each covering 0.09 square metres, that is 134 tiles before waste. Add 10% for straight layouts and 15 to 20% for diagonal patterns or rooms with many cuts. Always round up to whole boxes.
How much extra should I allow for cuts and breakage?
Ten percent is the standard minimum for a simple rectangular layout. Increase to 15% where there are many edges and obstacles, and to 20% for diagonal, herringbone or hexagonal patterns where nearly every perimeter tile is cut. Large-format tiles justify more allowance than small ones because a single bad cut wastes more area, and natural stone more than ceramic because it breaks less predictably.
Should I keep spare tiles after finishing?
Yes — hold back at least a square metre, and keep the box label. Tiles crack years later from dropped pans or settling, and matching a discontinued line is usually impossible. Replacing one tile from your own spares is a half-hour job; matching a discontinued line can mean retiling a whole area. Store them somewhere dry and remembered.
How do I account for grout lines?
For tile-count purposes you generally can ignore them, because using the nominal tile size slightly over-estimates coverage and that error works in your favour. Grout does matter for materials: joint width, tile size and depth determine how much grout and adhesive to buy, and those are usually quoted per square metre at a given joint width. Wider joints need proportionally more.
Do I calculate walls and floors differently?
The arithmetic is the same, but wall tiling needs more thought about layout. Deduct large openings such as windows and doors, then work out where the cut row falls — a sliver of tile at eye level looks poor, so tilers often shift the starting point to balance the cuts at top and bottom. That decision can change your tile count, so plan the layout before ordering.
What else should I buy alongside the tiles?
Adhesive and grout sized to your area and joint width, spacers at the chosen joint size, edge trim or bullnose tiles for exposed edges, silicone for internal corners and wet-area junctions, and a primer or waterproof membrane for bathrooms and wet rooms. Underestimating adhesive is common — coverage drops sharply on uneven substrates, where more is needed to bed each tile level.