Ordering cornice usually starts with a number, and the number people start with is a size: 90mm cornice, 75mm cornice, or whatever length the supplier list shows. The problem appears on site, when three rooms on the same floor end up with profiles that look inconsistent even though every measurement was quoted correctly. Size and length are two different decisions, and only one of them is about the product.

This guide covers what the size figure actually measures, how the common Australian sizes behave in Perth rooms, how stock lengths drive joint positions, and how to order quantities without a second trip to the supplier.

What the Number Means: Face Width Versus Projection

The number in a cornice size is the face width measured across the ceiling from the wall, not the projection down the wall and not the depth of the profile; two 90 mm profiles can project differently and read differently in the same room.

Establish the two measurements separately and record both. Face width runs along the ceiling plane from the wall corner to the outer edge of the profile. Projection runs down the wall from the same corner to the same outer edge. On a plain cove at 90 degrees the two are often similar, which is why the distinction is missed, but the relationship changes as soon as the profile is stepped, chamfered, or fixed to a ceiling that is not perpendicular to the wall.

Depth is the third number that suppliers rarely publish. It is the distance from the outer edge to the deepest point of the recessed face, and it decides how strong the shadow line is. A shallow 90 mm cove and a deep 90 mm cove are the same size on an invoice and different details in a room.

When you check a supplier’s range, read the product data rather than the heading. The published cove cornice range lists face widths and available lengths, and that is the information to compare against measured site conditions.

The Common Australian Sizes and the Rooms They Suit

The stocked plain cove range in Australia runs at roughly 55 mm, 75 mm and 90 mm face width, and each suits a different band of ceiling heights and room proportions rather than a different room type.

At 55 mm the profile reads as a fillet: it closes the junction, throws almost no shadow, and makes a low ceiling feel marginally taller by keeping the visual weight off the wall. At 75 mm it becomes a genuine transition, visible from across a room but not dominant. At 90 mm it carries a shadow line you can read from a doorway, and it needs ceiling height and room width to support it.

In practical terms, a 2.4 m ceiling in a standard-sized bedroom is comfortable with 55 mm to 75 mm. A 2.7 m ceiling with a larger floor area carries 90 mm well. Above 3 m, a 90 mm cove can start to look thin against a tall wall, and that is where stepped profiles and deeper sections are specified instead.

Ornamental profiles are the exception to the sizing rule. A cast reproduction is sized by its original mould and its ornament, not by a face width, which is why the ornamental cornice range cannot be compared to the plain cove range on numbers alone.

Face width against room conditions

Face width	Typical ceiling height	How it reads	Where it is usually specified
55 mm	2.4 m to 2.7 m	Barely a shadow; closes the junction	Compact rooms, apartments, secondary bedrooms
75 mm	2.4 m to 3.0 m	Visible transition with a soft shadow	Most residential work; the common middle choice
90 mm	2.7 m and above	Readable shadow line; adds visual weight	Living areas, entries, heritage rooms, feature spaces

55mm and 90mm Cornice Compared

The difference between 55 mm and 90 mm is not 35 mm of product; it is the difference between a junction that reads as a line and one that reads as a band, and it changes the whole perimeter of the room at once.

Measured straight, a 90 mm profile occupies 35 mm more of both the wall and the ceiling than a 55 mm profile. Around a four-wall room that is a continuous band running the full perimeter. On a wall carrying a window with a curtain track, those extra millimetres can be the space the track needed. On a wall carrying cabinetry to the ceiling, the extra depth can be the difference between a scribe and a rework.

Then there is the visual consequence. A 55 mm cove disappears in indirect light, so it never looks wrong and never looks like much. A 90 mm cove in a room that is too small reads as heavy, and because it is painted the same colour as the ceiling it reads as a thicker ceiling edge rather than a wider moulding. Reducing the profile is usually more effective than changing the paint scheme when a room feels closed in.

Where a project mixes the two sizes, keep them apart by floor or by room type. The same profile at 90 mm in a living area and 75 mm in a hallway reads as a deliberate reduction; 90 mm beside 55 mm at a doorway reads as an error.

Run Lengths, Joins and Wastage on a Real Room

Stock lengths decide where the joints land, and joint positions matter more than total quantity because a badly placed joint is the visible defect; plan the cut sequence before ordering, not after.

Start with the room perimeter and work the cuts so that each length is used as completely as possible while the joints fall in acceptable positions. Corners take mitres, so each length loses material at both ends. Work out the sequence wall by wall, then check how the off-cuts combine: an off-cut from one wall often completes the next, which is where the real saving in a room is made.

Allow for wastage, and allow for the fact that the run may not be straight. Older Perth homes have out-of-square junctions, and a length that measures 3.4 m along the wall may need a little more material to seat properly at the ends. A common allowance is a short length per room, and more where the junction is irregular or where a profile change needs a transition piece.

Check the length options on the range you intend to buy rather than assuming, because ranges differ: the same cornice catalogue covers cove, contemporary and ornamental profiles supplied in different lengths and thicknesses. Where a wall is longer than the longest stock length, the joint position becomes a design decision and should be agreed before the order is placed.

Sizing to Ceiling Height Before Proportion Tips Over

Size from the ceiling height first, because the profile is read against the height of the wall rather than against the size of the floor, and a profile that is proportionate to the height but too heavy for the room is easier to reduce than a profile that is too thin for the wall.

The ceiling height that matters is the height at the point where the profile can be seen along its run, which is usually the low side of any rake or the underside of any bulkhead. Measure the height at the lowest point of each wall, not in the middle of the room. Record the highest and lowest, and size to the lower figure.

Where a room steps in height, the profile should normally follow the highest ceiling and the step should be resolved with a transition detail rather than by changing the profile size at the step. This keeps the section consistent, which is what the eye compares.

Where the height suggests one size and the room’s width or function suggests another, the height wins. A large room with low ceilings is the one case where a heavier profile usually helps, because it articulates a ceiling that is otherwise blank. The nationally applied reference for ceiling heights in houses sits in the National Construction Code Volume Two, and the lining materials and installation that accompany cornice work are covered by the standards published through Standards Australia.

Sizing Against the Reveal, the Architrave and the Skirting

Cornice size has to be read against the other junctions in the room, and the common failure is a heavy cornice above a light skirting or a 90 mm cornice running into a door head with no room left for the reveal.

Above a doorway, the cornice has to terminate somewhere. A door frame set close to the corner leaves a short return of wall, and a deep profile cut into that return produces a cramped, visibly cut section. Where the door head is close to the ceiling, a smaller face width or a stopped run with a mitred return is the detail that works.

Skirting and architrave set the visual weight of the lower half of the room. A 90 mm cornice over a 90 mm skirting is balanced; the same cornice over a 40 mm skirting makes the ceiling look pressed down. This is one of the few places where the lower junction should influence the upper one.

Window heads and pelmets are the third constraint. Where a pelmet or a curtain box is specified, the profile must clear it, and where a window head sits close to the ceiling the cornice may need to be reduced or run through, depending on the detail drawn.

Ordering Quantities Without Overshooting

Order from the room schedule rather than from an estimate of the total perimeter, and reconcile the order against the cut plan so each wall is covered by whole lengths plus a defined allowance, with the join positions recorded.

Build the schedule room by room: perimeter, wall lengths, ceiling height, existing profile if any, and the number of corners. Corners are where quantities get underestimated, because each external or internal corner removes material from two lengths. Bulkheads, columns and any return around a recess add runs that are easy to omit from a quick measure.

Include the adhesive and joint filler in the same order. Cornice cement or the specified adhesive is consumed at a predictable rate per length, and a shortfall mid-job means a stop in the programme at the point where the sanding and painting trades are waiting. A rapid-set repair compound such as those listed in the manufacturer’s repair compound range is worth holding on site for the off-cut edges and any small section that has to be reset before the adhesive goes off.

Finally, keep the order sheet with the batch number where the supplier provides one. Where a run is being extended later, or a repair is needed after handover, knowing the exact range and size that was installed removes the guesswork. Our own cornice work records the profile, the material and the fixing method for each room as part of handover, and the same discipline is described in the guide to why cornice separates from the ceiling.