Coving Calculator
Enter your room dimensions and get the exact linear metres, number of 2m and 3m lengths, adhesive quantity and a cost estimate. Works for any room shape. 2026 UK pricing.
Fitting Guide
How to measure, choose and fit coving
A practical guide for DIYers, covering measurement, size selection, cutting corners and adhesive application.
How to measure a room for coving
Coving runs along every wall-ceiling junction in the room, so you need the total perimeter. For a rectangular room, add all four wall lengths: perimeter = 2 × (length + width). For an L-shaped or irregular room, measure every wall individually and add them together.
Add 10% wastage to allow for mitre cuts, breakages and off-cuts at corners. For a room with a chimney breast or alcoves creating lots of corners, add 15%. Use the calculator above for the exact count of 2m and 3m lengths.
Choosing the right profile and material
The three most common materials are expanded polystyrene (EPS), polyurethane (PU) and gypsum plaster. EPS and PU are the standard DIY choice — lightweight, easy to cut with a mitre box and installed with adhesive alone. Plaster coving is denser and more durable but significantly heavier; it needs temporary support (nails or props) while the adhesive sets.
For period properties (Victorian, Edwardian, Georgian), a decorative plaster cornice with stepped or ornate profiles will look more proportional than a plain cove. Use the size guide in the table above as a starting point, then assess visually once you've ordered a sample length.
Curved walls and bay windows: If your room has curved walls, you cannot use rigid plaster coving. You must use lightweight EPS or PU coving and cut it into short 100–150mm segments to follow the curve, filling the multiple joins with adhesive or filler before sanding smooth.
Cutting internal and external corners
Corners are the most difficult part of fitting coving. Each internal corner requires two pieces mitred at 45°. The critical thing most beginners miss is how to hold the coving in the mitre box — the coving must be held at the same angle it will sit on the wall and ceiling, not flat. Most mitre boxes designed for coving have a built-in stop for this.
External corners (e.g. on a chimney breast) are cut the same way but in the opposite direction. Mark pencil lines on the wall and ceiling first so you can see exactly where the coving edges will sit — this makes positioning much easier.
Stepped ceilings (extensions and knock-throughs)
A stepped ceiling occurs where one part of the room is lower than another — typically because of a downstand beam, an original ceiling kept beside a new lower one, or a knock-through that exposed different floor structures above. The vertical face of the step is usually 100–400mm tall.
Run coving along the perimeter of the higher ceiling first, finishing at the inside corner where the step meets the wall. Then run coving along the perimeter of the lower ceiling. Total perimeter is the sum of both — not the room's wall perimeter.
For the vertical face of the step itself: if 200mm or shallower, leave it plain — coving on a short vertical looks visually wrong. If over 200mm, add a small coving run along the lower edge where it meets the lower ceiling, mitred 90° at each end.
Mezzanine and split-level rooms
In loft conversions and double-height halls, part of the room may have a low ceiling under a mezzanine landing and part may extend to full roof height. Treat each section as a separate room for coving purposes.
Mezzanine underside: Cove the perimeter of the landing's underside as you would a standard ceiling. The vertical face of the mezzanine front (the part visible from the lower space) is left uncoved — a flat MDF or timber trim works better.
Upper level: Cove the perimeter of the upper ceiling normally, but stop the coving at the edge of the mezzanine opening with a stop end cap — not a mitre.
Vaulted to flat ceiling transitions
Vaulted ceilings in loft conversions, dormers and barn conversions often meet flat sections at a horizontal line. Standard plaster or polyurethane coving cannot follow the slope of a vault — its profile is designed for a 90° internal corner only.
Recommended: Cove the flat ceiling perimeter only, stopping where it meets the slope with a stop end cap. Leave the slope-to-wall junction uncoved or finish with a square shadow gap.
Specialist option: Bespoke pitched cornice cut to your vault's specific angle from heritage suppliers (Wm Boyle, Locker & Riley). Expect £40–£80 per linear metre versus £4–£12 for standard profiles. Rarely worth the cost outside listed-property restoration.
Worked example — L-shaped extension with stepped ceiling
Original 4×3m kitchen (ceiling at 2.4m) joined to a 3×3m extension (ceiling at 2.3m) by a 100mm downstand. The two rooms share one open 3m wall.
- Original kitchen perimeter (excl. opening): 4 + 3 + 4 = 11m
- Extension perimeter (excl. opening): 3 + 3 + 3 = 9m
- Step face: 100mm drop — no coving applied to the step itself
- Subtotal: 20m + 10% wastage = 22m
- Step transition allowance: +2m
Order: 24m of coving (12 × 2m lengths) plus 5 × 1kg adhesive tubs (approximately 1kg per 5 lineal metres).
Applying adhesive and holding while it sets
Apply coving adhesive as a thin, continuous bead along both the wall face and the ceiling face of the coving back. Press the coving firmly into position, sliding it slightly as you push to help the adhesive key in. Hold for 30–60 seconds, then use strips of masking tape across the face of the coving — angled down to the wall and up to the ceiling — to support it while the adhesive sets (typically 20–40 minutes).
Once all lengths are fitted, fill any corner gaps and nail holes with a fine surface filler. Sand smooth when dry, wipe off dust and apply a single coat of mist coat emulsion (50:50 diluted) before finishing with full-strength paint.
2m vs 3m lengths — which should you order?
Longer lengths mean fewer joins in the finished result, which is almost always better-looking. 3m lengths are the trade standard and are more economical per linear metre. The trade-offs are handling (harder to manoeuvre alone in a small space) and transport (you need a large vehicle or delivery).
For a typical UK living room, 3m lengths will give you 6–7 joins around the room instead of 9–10. In a hallway where lengths often run full-wall without a join anyway, the difference is less significant. The calculator above shows both options so you can decide based on your situation.
FAQs
Coving questions answered
Measure the perimeter of the room (add all four wall lengths together), then add 10% for wastage on cuts and corners. A standard 5×4m room has an 18m perimeter — you need approximately 20 linear metres including wastage. Use the calculator above to get your exact figure for any room size.
Match coving size to ceiling height. Standard rooms with 2.1–2.4m ceilings suit 90–100mm coving. Rooms with 2.4–2.7m ceilings suit 100–127mm. Ceilings over 2.7m look best with 127mm or a decorative plaster cornice. Using coving that is too small in a tall room looks lost; too large in a low room looks heavy and can make the ceiling feel oppressive.
Allow approximately 1kg of coving adhesive per 5 linear metres. A standard 1kg tub covers around 4–6m depending on how generously you apply it. For a 20m room, order 4 × 1kg tubs or 1 × 5kg tub. Always have one spare — running out before the adhesive goes off is a common and frustrating mistake.
3m lengths give fewer joins and a neater result. They are also more economical per linear metre. The trade-offs are that they are harder to handle alone in a small room and harder to transport without a large vehicle. 2m lengths are easier for a solo DIYer. Whichever you choose, the total linear metres needed stays the same — only the number of lengths and joins differs. The calculator above shows both options so you can compare directly.
Internal corners are cut at 45° in a mitre box, with the coving held at the angle it sits on the wall and ceiling — not flat. The two pieces meet to form a right angle. External corners (e.g. on a chimney breast) are cut in the opposite direction. Mark pencil lines on the wall and ceiling first so you can see exactly where the coving will sit before cutting. Cut, test-fit and adjust each corner before moving on — walls are rarely perfectly square.
Treat each ceiling level as a separate run. Cove the perimeter of the higher ceiling first, finishing at the inside corner where the step meets the wall. Then cove the perimeter of the lower ceiling separately. The vertical face of the step is normally left as plain plastered wall — coving on a step shorter than 200mm looks visually wrong. Total length needed is the sum of both ceiling perimeters, not the room perimeter.
Yes for the ceiling perimeters at each level, but the vertical face of the downstand itself is best left uncoved unless it is over 200mm tall. Short downstands (100–150mm, typical of extension knock-throughs) look better as a plain finished face. Tall downstands (300mm+) can be coved along the bottom edge to soften the transition. The most common mistake is trying to cove the vertical face — coving is designed for a 90° internal corner and does not work on a vertical-to-vertical junction.
Standard plaster or polyurethane coving cannot follow a vaulted slope — it is profiled for a 90° internal angle only. For the flat section, cove the perimeter and stop the coving with a stop end cap where it meets the slope, leaving the sloped section uncoved. If you specifically want coving on the slope, you need bespoke pitched cornice from heritage suppliers, costing £40–£80 per metre versus £4–£12 for standard profiles. For most domestic loft conversions, cove the flat section only — this is the architectural norm.
Add one extra 2m length of coving per step transition on top of the standard 10% wastage. Each transition requires two extra mitre cuts (one at each end of the step) and a short return — typically 200–400mm of finished material plus offcuts. For a room with two stepped sections, allow 4 extra metres beyond the standard wastage figure.
Both run along the wall-ceiling junction. Coving is a plain concave or simple ogee profile — typically lightweight polystyrene, polyurethane or plaster. Cornice is a more ornate decorative moulding, traditionally solid plaster, with stepped profiles, dentils or egg-and-dart detail. Cornice is heavier, more expensive and typically used in period properties. Coving is the standard choice for modern homes and DIY fitting.
Yes — lightweight polystyrene and polyurethane coving is very DIY-friendly. It is light enough to hold in place while you apply adhesive, forgiving of small corner gaps that can be filled, and easy to cut with a standard mitre box and fine-tooth saw. Plaster coving is more challenging — it is heavier and needs temporary support (props or masking tape) while the adhesive sets. Start with a small room to practise mitre cuts before tackling the whole house.
Yes, in almost all cases. Fitting over old coving gives a messy finish, makes mitre cuts at corners unreliable and risks the old coving pulling away from the wall and taking the new with it. Remove old coving, fill and sand any surface damage, then prime any bare plaster before fitting new. If the existing coving is solid plaster and bonded hard to the surface, seek a plasterer's advice before removal — it may be more trouble than it is worth to remove.
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