How the Coving Calculator Works

Enter your room’s length and width or total wall perimeter for irregular rooms and choose your coving length. The calculator works out perimeter, adds wastage and divides by length you are buying to give a whole number of pieces.

The core maths is simple: a 4m x 3m room has a 14m perimeter and with 10 percent wastage that becomes 15.4m, so eight 2m lengths or six 3m lengths. The judgement sits in wastage figure, because every mitred corner consumes material and a mis-cut mitre writes off the end of a length.

Choosing Lengths and Wastage

Coving comes in 2m and 3m lengths as standard, with some profiles in 2.4m. Longer lengths mean fewer joints along wall, which matters because joints are part most likely to show after painting. Buy the longest lengths your walls and your car can handle and plan so joints fall away from windows where light rakes across the ceiling line.

Wastage should match the room:

• Simple four corner room: 10 percent
• Rooms with 6 or more corners, chimney breasts or bay windows: 15 percent
• First time fitting coving: add a length or two for practice mitres, since the first corner rarely survives

Every internal and external corner pairs two 45 degree mitre cuts and a chimney breast alone adds four corners to a wall that looked straight on tape measure.

Cutting Mitres Without Tears

Mitres are where coving projects succeed or fail and one rule sorts most confusion, for an internal corner bottom edge of coving is longest on wall and for an external corner top edge is longest. Cut with coving upside down in a mitre box, held at same angle it will sit between wall and ceiling.

Two honest shortcuts exist. Pre formed internal and external corner pieces remove mitre cutting entirely at a small cost premium and suit a first project well. And decorator’s caulk covers small gaps at joints and corners before painting, which is not cheating, it is how trade finishes coving too.

Adhesive, Prep and Fitting Order

Coving adhesive goes on in a bead along both contact edges and a 1kg tub typically fixes 5 to 6 linear metres of standard lightweight coving, so a 15m room needs around 3kg. Heavier plaster coving uses more and may need mechanical fixing on larger profiles.

Preparation decides adhesion, mark parallel pencil lines on wall and ceiling using the coving’s drop and projection, score surfaces between lines and dust them off. Press each length to lines, support long pieces while adhesive grabs and fill joints as you go. Fit coving before painting ceiling and walls, since caulked joints and adhesive squeeze out disappear under paint but glare over it.

Coving Materials Compared

The material changes price, weight and forgiveness of the job. Polystyrene coving is cheapest and lightest, fine for low budgets but easily dented. Duropolymer and polyurethane profiles cost more, stay crisp, cut cleanly and suit DIY fitting best. Traditional gypsum plaster coving gives sharpest period profiles and takes paint beautifully, at cost of weight that makes it a two person job and less forgiving mitres. For most modern rooms a polyurethane profile in classic C shape hits the balance.