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Door measurements are only useful when every number has a label. A width described as “the door size” might mean the slab, frame, complete unit, finished opening, or rough structural opening. This draft guide explains the information to collect for an initial review; final production dimensions should follow the responsibility agreed for the project.
Know the five size terms
- Door slab: the moving door leaf.
- Frame or jamb: the assembly around the slab.
- Complete unit: door, frame, and any sidelights or transom.
- Finished opening: the completed visible opening.
- Rough opening: the structural opening prepared for the unit.
Tools and site information
Prepare a reliable tape measure, level, square where appropriate, notebook, pencil, camera, and a simple elevation sheet. Record the project location, floor reference, wall construction, and whether the existing frame will remain.
Measure width, height, and depth
Record width at more than one height and height at more than one position. Note the smallest readings and any visible irregularity, but do not decide installation allowances without the approved system. Record wall or jamb depth at multiple points where it matters.
Check square, level, and plumb
An opening can have similar widths but still be out of square or plumb. A competent installer or site professional should assess conditions that affect fitting. Photographs help explain the context but do not prove accuracy.
Record swing and handing clearly
Use a sketch showing the door viewed from an agreed side, hinge position, and swing direction. Avoid relying only on terms such as left-hand or right-hand because conventions can differ.
Add sidelights or a transom
Provide the total unit opening first. Then show the proposed door width, each sidelight width, and the transom split. Make the sum of component dimensions understandable on one elevation.
Photographs to send
- Straight-on view of the complete opening.
- Interior and exterior context.
- Head, sill, and both jambs.
- Floor level and threshold condition.
- Nearby wall, trim, switches, columns, or obstructions.
- Tape position for context, without treating a photo as final proof.
Common mistakes
- Sending one width and one height without labels.
- Mixing millimetres and inches.
- Measuring only the existing slab when a complete replacement is planned.
- Ignoring floor finish changes.
- Assuming an old opening is square.
- Failing to identify who confirms final production size.
Enquiry checklist
Send the labelled elevation, all recorded dimensions, photos, configuration, desired use, design references, and questions about frame, threshold, delivery, and installation. Mark preliminary measurements as preliminary.
