Coving / Crown Molding Calculator

How the coving and crown molding calculator works

This calculator estimates how many lengths of coving or crown molding a room needs. It takes the room perimeter, adds a wastage allowance for mitred corners and offcuts, divides by the length of one piece, and rounds up to whole lengths. It also returns an indicative cost from the price per length you enter. Coving runs around the join between wall and ceiling, so the perimeter is the figure that drives the quantity.

Measuring the perimeter

The perimeter is the total distance around the room at ceiling level — it is the sum of every wall, including the returns into bays, chimney breasts and alcoves. Door and window openings are not subtracted, because coving runs above them. A tape measure at ceiling height gives the most reliable figure; plans can understate the run where walls step in and out.

Coving wastage and mitres

The default wastage allowance is 10%. The main source of waste is the mitre cut at each corner: internal and external angles both consume length, and a miscut on a patterned profile cannot always be reused. Rooms with many corners, bays or breaks waste more than a simple rectangular room, so the allowance can be raised for complex layouts. Lengths bought a little longer than each wall run leave fewer joints along a wall.

What this tool does not do

It does not set out the mitre angles, account for a specific profile’s pattern repeat, or confirm the fixing method for your substrate. It does not replace a professional quote or factor regional pricing. Lightweight duropolymer and traditional plaster covings are fixed and finished differently, and the supplier’s data covers that.

On-site considerations

Coving is commonly sold in 2 m lengths, though 2.4 m and 3 m profiles are available; the length entered changes how the runs divide and how many joints fall along each wall. Longer lengths mean fewer joints but more offcut where a wall is shorter than a full length. Internal corners are usually mitred, while some plaster covings are scribed instead.

Adjusting the defaults

Every input here is editable. Enter your own perimeter, piece length, wastage allowance and price per length, and the count and cost recalculate instantly. If a default does not match your product or room, your own numbers always take precedence.

Using this coving calculator alongside other BuildMetricLab tools

This calculator works best as part of a wider plan. Pair the length with our project contingency and labour-cost calculators to build a complete estimate before contacting a supplier. All BuildMetricLab tools run entirely in your browser — no sign-up, no data sent anywhere, and every formula is shown on-page so you can audit the maths.