Construction
Door Trim Length Calculator
Estimate trim length for door casings from door width, height and door count.
Formula
Trim per door = two side lengths plus one top length (2 x height + width). Total = trim per door multiplied by number of doors.
How it works
Enter the door opening width and height. Each door needs two vertical trims and one header across the top. Multiply by the number of doors, then add a waste allowance for cuts and mitres when ordering.
FAQs
Does this cover both sides of the wall?
No, this is one face of one door. Double it for trim on both faces.
How much waste should I add?
Around ten percent is a sensible allowance for mitre cuts and offcuts.
What about the threshold?
Thresholds and stops are separate pieces and are not included in this casing length.
Rough estimate only — consult a licensed professional for structural work before building.