Plank and sheet flooring by the pack, with the skirting and underlay that go with it.
Painting, tiling and finishes. 5 questions answered below, each with the arithmetic behind it and the limits of what the tool decides. Open the Flooring Materials Estimator tool.
Flooring is the one finish bought in packs with a published coverage, which makes the arithmetic simple and the ordering easy to get wrong. Packs cover a stated area, cuts waste part of it, and the room's perimeter decides the skirting and the edge trims, which have nothing to do with the floor area at all. The estimator keeps the two apart. Area decides packs, perimeter decides skirting and trim, and the waste percentage sits between them as a visible line you control, since a straight lay in a square room and a herringbone in a hallway with six doorways do not lose the same proportion of a pack.
A room four point two by three point six is fifteen point one square metres. At two point two square metres per pack that is seven packs before waste, and eight with a ten percent allowance, which leaves a spare board and a half for the doorway and a future repair. The perimeter is fifteen point six metres, less one point eight for the doorways, so thirteen point eight metres of skirting. Underlay at fifteen square metres per roll means two rolls. The skirting did not change when the covering changed, which is the point of measuring the perimeter.
Timber and laminate in packs, tile and stone by area and box, vinyl in sheet or tile, and carpet by the square metre with its underlay. Each is bought differently, so the estimator applies the coverage the product states rather than a single rate. Where a product is priced per square metre you get an area, and where it comes in packs you get whole packs, because a part pack is not something a merchant will sell you.
Area divided by the coverage the pack states, then rounded up, with your waste percentage applied before the rounding. A pack that covers two point two square metres will not tile a four point two by three point six room into a whole number, so the seventh pack becomes eight with the allowance. Because the rounding happens once across all the rooms, a whole floor is cheaper in packs than the same rooms ordered separately.
Because skirting is a length, not an area. A square room and a long narrow room can share a floor area and differ by several metres of skirting, and the skirting is bought by the length. Doorways interrupt the run, so they are deducted, and the same perimeter gives you the edge trim and the scotia where the covering meets a wall it does not run under.
No, it is yours to set. A straight lay in a square room loses around five percent, a diagonal or herringbone in a hallway with several doorways loses fifteen or more, and a plank layout running through several rooms loses more again because the offcut at one end rarely fits the next. The percentage appears as its own line so a client can see what was allowed and why.
Levelling and preparation are outside the estimate. A subfloor that is out of flat needs a compound, which is a separate product with its own coverage, and one that is damp needs a membrane before anything is laid on it. Both are assessed on site rather than from dimensions, so the estimator asks instead of assuming, and a floor laid on a bad subfloor fails whether or not the pack count was right.