Structural Opening Guidelines

Determining the size of your structural opening is as simple as taking a few measurements and applying basic mathematics. Use our measuring tool guidelines below, capture the required sizes for your project.

Taking the right Measurements

Whether your sourcing a new internal door or replacing an existing production, our guide outlines how to capture your door size measurements correctly to ensure your that you are not left with an ill fitted door.

We recommend measuring in millimetres, as most accurate measurement allowing us to make sure your door will fit perfectly.

 “To get your door sizes you need to measure your existing door” – this is not the case.

To correctly measure your door size, you must base your measurements on the door frame – not the existing door your currently have.

Are you fitting new frames and doors? If the answer is yes, we would recommend you seek advice from our sales team (as a site visit will be required).

Real Wood Veneer door with Vision Panel

Where to Measure

Working upon the basis that you are keeping your existing frames you will require measurements of three areas these are structural opening width, height and door thickness.

Top Tip – put a star next to your largest value of each area this will allow you to quote them easier at the end of the measurements.

Structural Opening Width Measurements

Width of Structural Opening

Measure your opening from one side to the other, do this om three places: top, middle and bottom to make sure your opening is not smaller in one place than others.  The widest measurement will determine the width of the door.

Structural Opening Height Measurements

Height of Structural Opening

Measure the inside of each vertical side of the frame, from top to bottom (taking two recordings). The longest length is the determined height required.

Don’t forget to take the floor covering into account (laminate/ carpet etc) as the door may struggle to close if this hasn’t been considered.

Wall Thickness Measurements

Wall Thickness

Run the tape measure along the edge of the door and record the measurement of the thickness. Measure the wall thickness in five places around the opening, this will ensure the wall thickness is consistent.

Don’t forget to measure the frame rebate where door sits when closed also.

Does your project require a site visit?

Example of Door Size

Example of Door Size Measurements

We offer on-site measuring for large projects, in the case of smaller fit-outs to enable us to give the most accurate door sizes and measurements we will ask for a structural opening.

Use the below calculator as a guide to work out your door size. Clearance is the allowance we give around the door and frame.


Structural Opening  – Clearance = 

910mm – 10mm =  900mm 

Back to Back of Door Frame = 900mm

900 – 32 -32 – 3 -3 = 840mm 

This means door size width will be 840mm


Structural Opening – Clearance = 

2100mm – 10mm = 2100mm

Floor to Back of Door Frame = 2100mm

2100 – 5 – 3 – 32 = 2060mm

This means door size height will be 2060mm

Structural Opening Guideline Digaram Example