How to calculate skirting boards and cornice
Both skirting and cornice are measured in linear metres — the total length of all walls in the room (the perimeter). For a rectangular room, that's simply 2 × (length + width). Deduct doorway openings from skirting (cornice usually runs continuous over doorways). Then divide by the length of each piece to get the number of lengths to buy.
Skirting boards — what to know
Skirting boards are sold by the linear metre or in fixed lengths (usually 2.4 m or 3.0 m at Bunnings and timber yards). MDF skirting is the most common choice in Australian renovations — it's pre-primed, takes paint well and is significantly cheaper than timber. Timber skirting (pine, hardwood) is used where a natural finish or staining is needed.
Standard heights are 67 mm, 90 mm and 120 mm. Taller skirting (120 mm+) suits period homes and higher ceilings; 67–90 mm is standard for contemporary builds.
Cornice — what to know
Cornice (also called coving) runs along the join between wall and ceiling. It's almost always plaster or MDF and sold in lengths of 3.6 m or 5.4 m. The most common profile in Australian homes is cove cornice (a simple curved profile) — typically 55 mm or 90 mm. Federation and heritage homes use more ornate profiles.
Cornice is usually installed before painting and runs continuous — unlike skirting, it doesn't stop at doorways.
Joining lengths — the waste reality
Every internal and external corner requires a mitre cut, and joins along straight runs waste the offcut. The 10% waste margin accounts for this. In rooms with many corners, alcoves or bay windows, bump the margin to 15%. Always buy one extra length as insurance — running short mid-job means a trip to the supplier and potential batch colour mismatch.
Installing over existing skirting
If you're adding new skirting over existing (a common renovation approach), measure the existing skirting height and buy a profile that sits flush or overlaps cleanly. Most joiners recommend removing and replacing rather than doubling up — but for a quick refresh, over-skirting kits are available at Bunnings.