Skirting and trim take-off

Metres run, mitred corners and whole lengths — a take-off in one dimension

The perimeter is gross, and the doorways come off it. A skirting board stops at each architrave, so every door opening is perimeter the profile never crosses. The deduction is the opening count times a typical opening width — and it is a deduction worth making, because in a small room with two doors it can be a noticeable slice of the whole run.

Corners are where the cutting waste is earned. An external corner is mitred, an internal one on a shaped profile is scribed over its neighbour, and both cuts eat length beyond the wall’s face measurement; a room with many returns, a chimney breast or boxed pipework spends more of every board on its angles. The waste percentage stands in for all of it, plus the splits and mis-cuts every fixing job produces.

The stock length dictates the join problem. Profiles are sold in standard sticks, and a wall longer than one stick needs a joint — ideally a scarf on a stud, never a butt in mid-air — while a wall shorter than one leaves an offcut that may or may not survive to serve a shorter wall later. Longer sticks mean fewer joints and often less waste, at the price of handling and delivery.

The engine answers in both currencies: the gross length to order, and how many standard sticks that length represents. The piece count is left unrounded deliberately — a count a whisker past a whole stick is the signal to plan the cutting list so an offcut serves the last short wall, rather than to buy a board that will lean in the garage.

The same line prices more than skirting. Dado rails, picture rails, coving at the ceiling and quadrant beading at a floor edge all follow the room’s perimeter with their own opening rules, so the arithmetic transfers — only the judgement about what interrupts the run changes from profile to profile.

When this calculation is used

• Ordering skirting once a room’s perimeter is measured and its door openings counted.
• Pricing any perimeter-following profile — dado, picture rail, coving, beading — by the same run-minus-openings logic.
• Checking a joiner’s materials list by reproducing it from the perimeter, the openings and a stated waste.
• Choosing between the merchant’s stock lengths by seeing what each does to the piece count and the joins.

Worked example

The pack’s declared vector: a room with twenty metres of perimeter and a single door opening at the default width, the default tenth of cutting waste, and a profile sold in three-metre sticks.

Two figures come back: the length to order once the doorway is deducted and the waste applied, and the unrounded count of sticks it becomes. Read the fraction on the count against the room’s shortest wall — that is what decides whether the last stick’s offcut finishes the job or a further stick is genuinely needed.

Every figure in this example is produced by the certified engine when the calculator loads, checked against the signed pack’s declared test vectors; nothing on this page stores an answer. Add a second doorway and watch the order shrink — this is the one take-off in the cluster where openings subtract instead of the surface adding.

What each input represents

Assumptions and limits

• The profile follows the full perimeter except at door openings; fitted wardrobes, stair strings and other fixed interruptions should be deducted by lengthening the opening allowance or trimming the perimeter.
• Waste is a single flat percentage for mitres, scribes, joins and mis-cuts; rooms dense with corners deserve a heavier figure than the long plain runs the default imagines.
• Every stick is the same standard length, and offcut reuse across walls is the fitter’s cutting-list craft — the model prices the run, not the packing problem.
• The result is the profile alone: adhesive or fixings, caulk at the wall line and decorating are their own lines, and species or MDF choice belongs to the merchant’s catalogue.

What the guards protect against

• Door deductions that meet or exceed the perimeter are refused outright, and the pack ships the refusal as a declared test vector: a room whose openings outmeasure its walls is a mis-count or a unit slip, and the engine reports it as bad input rather than returning a negative run of skirting.
• The cutting wastage is held to the range trim take-offs actually use, with its own declared refusal vector — beyond three tenths the room’s corners are not the problem, the measurement is.
• The perimeter, opening width and stick length must all be strictly positive: the piece count divides by the stick length, so a zero there is refused before it becomes a count without meaning.

Provenance

Chudley and Greeno, Building Construction Handbook (quantity take-off conventions)

Net run as the perimeter minus the door openings at their entered width; the order as that run grossed up by the cutting waste; the piece count as the grossed run divided by the standard stick length, reported unrounded.

Quantity reference to be verified against the room and the profile actually chosen; fixing method and finish are never determined here. The signed pack carries its own citation, and the page reports the verification state of the release it mounted.