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Coving Length Calculator

Enter your room size and get the coving metres and packs to buy.

How it is calculated

The tool treats the room as a rectangle: perimeter = 2 × (length + width), in metres. It then adds the waste allowance, coving needed = perimeter × (1 + waste ÷ 100), and divides by the length of one pack, packs = ceil(needed ÷ pack length), always rounding up to a whole pack. Pack length is the total metres of coving in one pack you buy, not the length of a single piece, and the tool has no field for pieces per pack. Length, width and pack length must be above zero, waste must be 0 or more and below 100, and the waste field cannot be left empty. Doorways, chimney breasts and bay windows are not modelled, so measure those separately.

Worked example

A room 4.2 m by 3.5 m, bought in 3 m packs, with 10 % waste. Perimeter: 2 × (4.2 + 3.5) = 15.40 m. With waste: 15.40 × 1.10 = 16.94 m of coving. Packs: 16.94 ÷ 3 = 5.65, rounded up to 6 packs, which gives 18 m and leaves about 1 m spare.

Try this example →

Common mistakes

  • Entering the length of one piece when the field asks for the whole pack: if a pack holds four 2 m pieces, enter 8, not 2.
  • Leaving the waste box empty, thinking blank means none; the field must contain a number, so type 0 if you want no allowance.
  • Entering the room in feet or centimetres: the fields are metres, so 420 for 4.2 m would give a hundredfold result.
  • Applying the result to an L-shaped or alcoved room: the tool uses one length and one width, so for those, add up every wall yourself.
  • Setting waste to 0 for a room with many corners: mitre cuts leave off-cuts you cannot always reuse.

About this calculator

Coving (also called cornice) is the decorative moulding installed along the join between wall and ceiling, and calculating how much you need is simply the room's total perimeter — the sum of all four wall lengths — increased by a waste allowance, divided by the length of coving in one pack (commonly sold in 2m or 3m lengths) and rounded up to whole packs.

Decorators and DIY homeowners calculate this before ordering coving because miscalculating the perimeter or forgetting to round up for waste at internal and external corners (where pieces need to be mitred and off-cuts can't always be reused) is one of the most common reasons a job gets held up waiting for an extra pack to arrive mid-installation.

Room length and width give the perimeter; add the waste allowance, divide by the length of coving in a pack, and you know the metres needed and exactly how many packs to buy.

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