Summary

Skirting board quantity looks like the simplest calculation in second-fix carpentry — measure the walls, buy that much board — but it's a common source of under-ordering because two things get missed: door openings should be deducted (skirting doesn't run across a doorway), and the waste allowance needs to reflect the joint strategy, not just the room shape. A room with four scribed internal corners wastes more board than the same room fitted with butt joints at every wall, because scribing removes material from every board it's cut against.

Getting the linear metreage right matters commercially in two ways. Under-ordering on a job with an awkward-to-match profile (a period ogee or torus profile not readily available off the shelf, see skirting architrave) can mean a delay of days waiting for a merchant reorder or a bespoke run from a joiner, holding up the whole second-fix and decoration schedule behind it. Over-ordering ties up cash in material that either goes to waste or has to be returned, and merchants don't always accept returns on cut-to-order or specialist profiles.

The calculation itself has two parts: working out the total run length needed (perimeter minus openings, plus waste), and working out how that run length translates into a number of stock-length boards to buy, accounting for joins. Both parts matter — a room with a long, uninterrupted wall run might need fewer boards than the linear metreage alone suggests if long stock lengths are available, or significantly more if the merchant only stocks short lengths and every wall needs a joint.

Key Facts

Quick Reference Table

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Room Type Typical Waste Allowance Notes
Simple rectangular room, standard corners 10% Baseline allowance
Room with 1 chimney breast or similar external corner feature 12–15% Extra mitres, slightly more offcut
Room with bay window 15–18% Non-standard angles, more joints
Room with multiple alcoves/boxed pipework 15–20% More corners, more scribes, shorter runs
Small room (cloakroom, en-suite under 6m² floor area) 15–20% High offcut-to-total-length ratio even if shape is simple
Whole-house second fix (multiple rooms, one order) 10–12% blended Offcuts from larger rooms can sometimes be used on smaller ones

Detailed Guidance

Step 1 — Measure the room perimeter

Walk the room with a tape measure (or laser measure) at skirting height, recording each wall length in sequence. For a straightforward rectangular room, this is simply 2 × (length + width). For anything more complex — a bay window, a chimney breast, an alcove — measure each individual wall section rather than trying to shortcut with an overall room dimension, because the actual wall-run length around a bay or chimney breast is longer than the straight-line room dimension would suggest.

Total perimeter = sum of all individual wall-face lengths

Step 2 — Deduct door openings

Subtract the width of every door opening from the total perimeter — skirting does not run across a doorway, it stops at the door lining on either side.

Net linear metres = Total perimeter − sum of door opening widths

Do not deduct for radiators, built-in furniture, or other obstructions that skirting runs behind — skirting is still fitted (and therefore still needs to be bought) in those sections, even though it may be scribed around a pipe or covered later by furniture.

Step 3 — Add waste allowance

Order length (before rounding to stock lengths) = Net linear metres × (1 + waste %)

Use the table above to select the appropriate waste percentage for the room's complexity.

Step 4 — Convert to number of stock boards

Divide the order length by the stock board length available, and round up to the nearest whole board. If the merchant stocks multiple lengths, consider which combination minimises both joints and waste — this is a judgement call rather than a pure calculation, since buying one long board to cover a run with only a small amount of otherwise-wasted length remaining can be more economical than buying two shorter boards.

Number of boards = ROUND UP (Order length ÷ stock board length)

Worked example 1 — simple bedroom

A rectangular bedroom, 4.2m × 3.6m, with one standard 826mm door opening. Using 3.6m stock length skirting boards.

Worked example 2 — living room with chimney breast and bay window

A living room, 5.5m × 4.0m with a projecting chimney breast (adding roughly 1.2m of additional wall-face length for the two returns) and a bay window (adding roughly 1.8m of additional wall-face length across three angled sections), one door opening at 926mm. Using 4.2m stock length MDF skirting.

Worked example 3 — small en-suite with awkward corners

A small en-suite, 2.4m × 1.8m, with a 686mm door opening and boxed-in pipework adding one extra internal and one extra external corner. Using 2.4m stock length softwood skirting.

This example illustrates why small rooms need a proportionally higher waste allowance — even a modest room generates enough offcut loss from corner cuts and the door opening deduction that the waste percentage has a bigger relative impact than on a large open room.

Cross-checking against the profile availability

Before finalising the order, confirm the specified profile is available in the stock length assumed in the calculation. A period ogee or torus profile matched to an existing Victorian skirting run may only be available as a custom joinery run in shorter lengths (often 3.0m maximum from a small joinery shop, rather than the 4.2–5.4m lengths common for standard modern profiles) — this changes both the number of boards and the number of joints, and should be confirmed with the supplier before quoting the job, not discovered on delivery day.

Architrave — a separate calculation

Door and window architrave is calculated independently of skirting, even though both are second-fix trim purchased and fitted at the same stage. A standard single door opening needs roughly 5–5.5m of architrave (two legs at approximately 2.0–2.1m each, plus a head piece of around 0.9–1.0m, plus waste for the 45° mitres at each top corner) — see skirting architrave for jointing detail and second fix carpentry for the full second-fix sequence and reveal/margin specification.

Frequently Asked Questions

Do I need to deduct for a bay window's angled sections, or add for them?

Add. A bay window's wall-face perimeter (following the actual angled wall sections around the bay) is longer than the straight-line width of the bay opening as measured from the room's main wall plane — measure each angled section of the bay individually and add them to the total perimeter rather than trying to approximate with a single straight-line measurement.

Should I round the door opening deduction to a standard size, or measure on site?

Always measure on site. Standard door opening widths (686mm, 762mm, 838mm leaf plus lining, giving overall openings commonly around 762mm, 826mm or 926mm) are a useful sanity check, but older properties, non-standard doors, and previous alterations mean actual openings vary. A wrong assumption compounds across every doorway in a whole-house quote.

Why does a small room need a higher waste percentage than a big one?

Because waste from corner cuts, scribes and the door opening deduction is roughly constant in absolute terms (a scribed corner wastes a similar amount of material whether the room is large or small) but represents a much larger percentage of the total linear metreage in a small room. A 400mm loss on a 9m total run is over 4%; the same 400mm loss on a 25m run is under 2%.

Can offcuts from one room be used on another room in the same job?

Sometimes, if the profile and colour/finish match and the offcut is long enough to be useful (generally anything under 500–600mm isn't worth transporting and storing between rooms). On a whole-house second fix, it's reasonable to apply a slightly lower blended waste percentage across the full order because offcuts from larger rooms can often cover short runs elsewhere — but don't rely on this for the initial order; order per room and true up any genuine shortfall once cutting is underway.

Regulations & Standards