Flooring and tile dimensions

Flooring is chosen by appearance and installed as arithmetic, and the two get introduced to each other far too late. The decisions have a strict order: how thick the finished stack is, then what format sits on top of it, then how wide the joints between units are, then where the first line goes, then how the floor meets everything at its edges. The first decision is the one that cannot be undone, because it is the only one that changes the height of the room.

Build-up is the first number, and it is measured to the finished surface#

The useful figure is never the thickness of the board. It is the difference between the old finished level and the new one, because everything already in the room was set to the old one: the door undercut, the appliance apertures, the bottom of the stair, the threshold at the front door.

Compare that column with the gap under your doors before anything is ordered. The full stack including acoustic layers is in underlay and subfloor thickness, and the consequences at doors and appliances in floor height changes, doors and appliances. Stairs pay twice, because the tread build-up and the riser height change together and the top riser is the one that fails: see stair tread and riser flooring dimensions alongside the tolerances in stair dimensions.

Format: width, length and the size of the room#

Once the height is settled, format is a proportion decision. Plank width bands sit at 3 to 5 in (76 to 127 mm) strip, 5 to 7.5 in (127 to 190 mm) plank, and 7.5 to 10 in (190 to 254 mm) wide plank. Wider boards show fewer lines and more of each board's movement, so they demand a flatter subfloor and a tighter moisture regime. Length distribution matters as much as width, and short random lengths in a large room read as busy no matter how good the timber is. The bands and their room-size logic are in floor plank widths, lengths and proportions.

Tile runs to its own module, and the perimeter cut is the number that decides whether a layout works: aim never to finish with a strip under 50 mm (2 in) or half a tile, whichever is larger. Tile sizes and layout dimensions sets out the grids, and herringbone and chevron layout dimensions covers the two patterns where the border is a dimension in its own right and waste climbs to 20 to 25 per cent. Carpet is a third system again, sold in 12 ft (3.66 m) and 15 ft (4.57 m) rolls, so seam positions are decided by the roll and not by the room: carpet roll widths, seams and pile. Quantities in either system come out of tile and flooring quantity conversions or the tile and flooring quantity calculator.

Joints: the grout line and the expansion gap are the same idea#

Both are movement allowances, and both are sized by how much the assembly will move and how accurate its units are. A grout joint absorbs the size tolerance of the tile: rectified porcelain is ground to size and takes 1.5 to 2 mm (1/16 in), pressed ceramic varies enough to need 3 mm (1/8 in), and handmade tile needs 5 mm (3/16 in) or the courses wander.

An expansion gap absorbs seasonal movement of the whole field. Ten millimetres (3/8 in) is the default at every wall, plus about 1 mm per metre of run past 10 m (33 ft), and it must be present at pipes, thresholds and door linings as well, not just the two walls the fitter can see. Both are worked through in grout line widths and joint sizing and expansion gaps and perimeter details. The gap is normally covered by the skirting, which is why the baseboard height in baseboard and skirting heights has to be confirmed before the floor is laid rather than after.

Setting out: where the first line goes#

Setting out is decided by sightlines, not by the longest wall. Run planks along the main sightline or the length of the room, square the first row to a chalk line rather than to a wall that is not straight, and balance the cuts so both perimeter courses are equal. Long units get a maximum stagger of one third of their length: a half-bond puts every end joint at the crown of the unit below, which is where lippage is worst.

Out-of-square rooms make this a real calculation rather than a habit, and out-of-square rooms and tolerance gives the method for splitting the error across two walls instead of dumping it all on one.

The edges are where floors fail#

Almost every visible flooring defect is an edge condition: a sliver cut at a doorway, a threshold that trips, a skirting that no longer covers the gap, a rug whose pad lifts the pile above the door swing. Rugs deserve a mention here because they are the one floor layer added after everything else is fixed, and a 10 mm pad under a 12 mm pile is 22 mm of new height under a door that was trimmed for a bare floor, which is the argument of rug pad sizes and thicknesses.

Decide the edges on paper first. The field of a floor takes care of itself.