What wastage percentage should I add when cutting timber?

For rough solid timber, add 15–20 %. For MDF or plywood boards, 10 % is usually enough. For precision work with tightly fitted pieces, it can be reduced to 5 %.

How do I calculate the amount of boards for a wood floor?

Divide the total area (m²) by the board width and add the wastage percentage according to the laying pattern.

What is the density of pine wood?

Pine has an approximate density of 500–600 kg/m³ depending on species and drying grade. Oak is around 700–750 kg/m³.

Crown Molding Calculator

Last updated: 2026-06-23

Use the Crown Molding Calculator to get instant, accurate results. Enter your values below.

Inputs

Result

Enter values and press Calculate

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Common Sizes — Click to Fill

	Room length (m)	Room width (m)	Molding piece length (m)
Small door	2.5 m	2 m	2.4 m
Standard door	3.75 m	3 m	2.4 m
Large door	5 m	4 m	2.4 m
Window	7.5 m	6 m	2.4 m
Bay window	10 m	8 m	2.4 m

What is the Crown Molding Calculator?

Crown molding runs along the ceiling perimeter of a room, and ordering the right linear metres is critical — molding is sold in fixed lengths (typically 2.4 m or 3.6 m) and joins are visible if you use short off-cuts. This calculator computes the room perimeter, adds 10% for angled cuts and waste, and tells you how many lengths to buy.

You may also find the Baseboard Calculator, Decking Calculator, and Fence Picket Calculator useful.

Who Uses This Calculator?

This tool is used by homeowners installing crown molding, finish carpenters quoting trim jobs, and interior designers specifying millwork.

How to Use the Crown Molding Calculator

Enter your Room length.
Enter your Room width.
Enter your Corner type.
Enter your Molding piece length.
Click Calculate to see your results instantly.

Formula

The calculator uses the following formula:

Perimeter = 2 × (length + width); Linear metres needed = perimeter × 1.1; Pieces = ceil(linear_m ÷ molding_length)

Worked Example

A 5 m × 4 m room with 90-degree corners requires 18 m of molding perimeter. Adding 10% waste gives 19.8 m — so buy 9 lengths of 2.4 m molding (21.6 m total).

Step-by-Step Calculation

Room perimeter: 2 × (5 + 4) = 18 m
Add 10% for mitre cuts and waste: 18 × 1.1 = 19.8 m
Pieces of 2.4 m: ceil(19.8 ÷ 2.4) = 9 pieces

Common Mistakes to Avoid

Not adding extra for mitre cuts — each inside corner wastes ~5 cm per piece
Forgetting to measure the height at which crown contacts the wall and ceiling
Ordering standard lengths without checking if longer pieces reduce waste

Pro Tip: Use a compound mitre saw for crown molding corners — the dual-angle cuts are difficult to do accurately with a standard mitre box. For large rooms, use longer molding lengths to minimise joins.

Frequently Asked Questions

How do I cut crown molding corners?

Crown molding corners require compound mitre cuts — typically 45° mitre and 33.9° bevel for 90-degree inside/outside corners. A dedicated crown molding mitre setting on your saw makes this easier. Test cuts on scrap before cutting good stock.

What is the waste allowance for crown molding?

10% is standard for rooms with 90-degree corners. Add 15–20% if the room has many corners or bay windows, since each corner requires angled cuts that waste material.

Should crown molding be nailed to studs or the top plate?

Crown molding should be nailed at 45 degrees into both the ceiling and wall — hitting studs and ceiling joists where possible. Use a stud finder first. Finish nails (50–65 mm) with a nail gun give the cleanest result.

How do I fill gaps between crown molding and the wall?

Use paintable latex caulk, not silicone. Apply a thin bead along the top and bottom edges, smooth with a damp finger, and paint after it dries. Small gaps (< 3 mm) are expected and easily caulked.

Can crown molding be installed on vaulted ceilings?

Yes, but it requires raking crown molding that runs at the slope of the ceiling, not horizontal. The calculations are more complex. For dramatic vaults, consider cove molding which is more forgiving to install.

Written and reviewed by the CalcToWork editorial team. Last updated: 2026-06-23.