Illustrated terminology sheet
Door frame, lining and casing: what is the difference?
A frame is the broad assembly around a door leaf; in ordinary UK internal-door work, lining commonly names the timber head-and-jamb assembly fitted inside the opening. Casing is less dependable: some sources use it for the lining, while decorative trim is usually called architrave here. Read the document in front of you, because usage varies.
Terms before dimensions
Direct comparison
One doorway, several layers.
Frame
The general name for the fixed assembly surrounding and supporting the moving leaf. “Door frame” is also used conversationally for internal and external work, so the word alone does not identify the exact measuring surface.
Lining
A common UK term for the timber assembly fitted into an internal opening. It has a head across the top and jambs down the sides; a stop may be fixed or added inside it to limit the leaf’s closed position.
Casing
A term that needs context. The British Woodworking Federation glossary describes casing as the timber lining of a door opening, while merchant guidance notes that frame, lining and casing usage is not strict. This page therefore does not declare casing a universal synonym.
Terminology is attributed to the BWF joinery glossary and qualified by the Door Superstore terminology source. The BWF wording is industry-body usage, not proof that every maker or region labels parts identically.
Members and surfaces
Jamb, head, stop and reveal are not the whole frame.
A jamb is a vertical side member. The head is the top horizontal member. The BWF glossary supports those two descriptions and defines a reveal as the vertical side of an opening in a wall. In other words, “jamb” names a member of the surrounding assembly; it is not another name for the entire frame.
A stop is the slim piece inside the lining against which the closed leaf is positioned, according to the merchant terminology source. Separately, the BWF glossary describes a rebated edge as one cut to form a step, usually as part of a joint. That neutral definition does not establish where a rebate is used, any relationship to a stop, or universal dimensions. Record what is physically present rather than assuming the section from its name.
Visible finish
Casing is not automatically UK architrave.
For this guide, architrave means the decorative moulding that covers the join between wall and frame. That follows ordinary UK DIY wording in the Wickes architrave source. It sits over the face of the join; it is not the surface against which the leaf closes.
By contrast, BWF’s glossary uses casing for the timber lining of a door opening. Other instructions may use casing more broadly. Do not translate casing to architrave or lining silently: look at the drawing, bill of materials or section and annotate which physical piece the author means.
Moving part / fixed context
The leaf belongs to the doorway, not to the opening measurement.
The door leaf is the moving panel named as a component of a timber doorset by the Door & Hardware Federation source. The lining or frame, head, jambs, stop, reveal, architrave and any threshold describe surrounding members, surfaces or trim. A leaf width therefore cannot stand in for a lining width or wall-opening width.
When you measure, declare the mode first: existing leaf, inside the frame or lining, or the wider wall opening. Note whether the tape meets a stop or rebate and whether a threshold or future floor finish affects height. Take three widths and three heights where the measurement worksheet calls for them. Do not add a generic allowance or convert a leaf row into an opening size.