How to Calculate the Moldings and Crown Pieces Your Room Needs

To calculate moldings (long strips), multiply the room perimeter by a suitable waste allowance, divide by the piece length and round up. Crown pieces are decorative elements counted by number according to your design. For an instant result, use the quantity calculator on the site.

Terms

Many people say "cornice" for the long strips; here we call them moldings. In the store you will find GRP panel moldings at 1.5 m per piece. A crown piece is a standalone decorative element counted by number, not by length.

1. Long moldings

1. Perimeter: room perimeter = 2 x (length + width).
2. Waste: cutting and corners use up some length. A 10% allowance is a reasonable start, more for rooms with many corners.
3. Divide: pieces = (perimeter x 1.1) / piece length, rounded up.

Worked example: a room 5 m by 4 m has a perimeter of 2 x (5 + 4) = 18 m. With 10% waste that is 19.8 m. With 1.5 m pieces, 19.8 / 1.5 = 13.2, so round up to 14 pieces (21 m in total).

2. Frames and their corners

For a panel made of repeated frames on a wall, first count the frames, then the corners and molding lengths:

• Frames across = (wall width - gap) / (frame width + gap), rounded down.
• Frames down uses the same formula with the vertical dimensions.
• Panel corners = 4 per frame.
• Molding length = frames x 2 x (frame width + frame height), then add waste.

Worked example: a wall 3 m wide and 2.6 m high, frames of 60x80 cm with a 10 cm gap. Across: (300 - 10) / (60 + 10) = 4.1, so 4. Down: (260 - 10) / (80 + 10) = 2.8, so 2. That is 8 frames needing 32 panel corners. Molding length = 8 x 2 x (60 + 80) = 22.4 m, about 24.6 m with 10% waste, and 24.6 / 1.5 = 16.4, so 17 pieces of 1.5 m.

3. Crown pieces

Crown pieces are spaced along the wall according to the design. For a repeating row, divide the available length by (piece width + desired gap). On a 4 m wall with a 40 cm piece and a 20 cm gap: 400 / 60 is about 6.7, so 6 pieces, then spread the leftover space evenly so the gaps match. Each crown's size is on its product page.

Tips for accuracy

• Measure twice before ordering and write the numbers down.
• Always round up, and order everything from the same batch so colour and size match.
• Add a spare piece if the design is complex or there is a lot of cutting.
• Check the matching molding in each corner's description before you calculate lengths.
• The calculator also estimates paint quantity.

Try it now on the quantity calculator page and add what you need to your order. Examples: molding G240 and molding G220.