How do I calculate door casing length?

For a three-sided casing layout, add two vertical runs equal to the opening height plus one horizontal run equal to the opening width, then multiply by the number of doors and add the required allowance.

Does door casing go around all four sides?

Many door casing layouts use three sides because the floor side is not normally trimmed in the same way. Actual trim details vary by design.

Should I add waste to casing length?

Yes, a practical allowance can account for cuts, mitres and unusable offcuts.

Does the calculator optimize miter cuts?

No. It estimates total linear material and stock-piece quantity.

Door trim takeoff

Door Casing Length Calculator | Trim Around Openings

Estimate the linear casing material needed around multiple door openings. Choose the number of trimmed sides, add a cutting allowance and convert the result into practical stock-piece quantities.

Door casing inputs

Number of doors

Opening width

Opening height

Trim sides

Casing stock length

Cutting / miter allowance (%)

Enter opening dimensions and door count.

Casing material requirement

Planning quantity

—

Linear casing material

—m per door

—Net length

—Planning length

—Stock pieces

—

How door casing length is calculated

3-side casing = 2 × opening height + opening width
4-side casing = 2 × opening height + 2 × opening width
Planning length = net casing × (1 + allowance ÷ 100)
Stock pieces = ceiling(planning length ÷ stock length)

Why the number of sides matters

Many door trim layouts use two vertical legs and one head piece, but some decorative or alternate trim systems use four-sided arrangements. The selector keeps that design choice explicit.

Why a stock-piece count can be larger than the length suggests

Door casing is cut into discrete pieces. Mitres, end cuts and short unusable offcuts mean that a linear-foot or linear-metre total cannot by itself guarantee a perfect cut plan. The stock-piece result is therefore a simple procurement screen rather than a cutting optimizer.

Worked example

For six doors, each 900 mm wide and 2,100 mm high, using three-sided casing:

Per door = 2 × 2.1 + 0.9 = 5.1 m
Net = 6 × 5.1 = 30.6 m
With 12% allowance = 34.27 m

If casing is supplied in 2.4 m lengths, the simple stock-piece estimate is the planning length divided by 2.4 m and rounded upward.

Frequently Asked Questions

Does this include waste?

Yes. The allowance is an explicit input.

Can I use four-sided casing?

Yes.

Does it optimize cuts?

No. It estimates linear material and standard stock-piece quantity.

Should casing around an opening match the door width?

The casing normally follows the actual trim layout around the opening rather than the nominal door leaf alone.