How to Measure for a Security Door: A Step-by-Step Guide
A clear step-by-step guide to measuring a doorway for a security door: where to measure width and height, why you take the smallest reading, how to note the hinge side and frame depth, and when a free professional measure is the safer choice.
Key product notes
- Measure the width at the top, middle and bottom of the opening, and the height on the left, centre and right.
- Always order to the smallest reading so the door fits the tightest point of the opening.
- Note the hinge side, the frame depth and any obstructions before you order.
- Shire Security Doors and Screens measures every opening free of charge across the Sutherland Shire on 0410 474 256.
How do you measure for a security door?
Measure the width at three heights and the height at three points, then order to the smallest reading. Take the width across the inside of the door frame at the top, middle and bottom, and the height on the left, centre and right. Openings are rarely perfectly square, so the smallest figure is the one that lets the door fit cleanly without binding or leaving a gap.
This guide walks through each measurement in order, explains why the smallest reading matters, and shows how to note the hinge side and frame depth. It also covers when a free professional measure is the smarter choice, because a custom security door is made to your exact opening and there is no margin for a guessed figure.
- Measure width at top, middle and bottom
- Measure height on the left, centre and right
- Order to the smallest reading of each
- Note hinge side, frame depth and any obstructions
Step 1: Measure the width at three points
Use a steel tape and measure the clear width of the door frame at the top, across the middle, and at the bottom. Measure between the inside faces of the frame where the door will sit, not the architrave or the outside of the timber. Record all three figures in millimetres, because timber frames and brick reveals often move out of square over the years and the three readings can easily differ by several millimetres.
If the readings vary, do not average them. The width that matters is the narrowest of the three, since a door built to the widest point would jam against the tightest part of the frame. Keeping all three numbers written down also helps your installer see whether the frame needs packing or adjustment.
- Measure between the inside faces of the frame
- Take readings at top, middle and bottom
- Record every figure in millimetres
- Keep all three numbers, do not average them
Step 2: Measure the height at three points
Now measure the height of the opening from the sill or threshold up to the underside of the head, on the left side, the centre and the right side. As with the width, an old opening can be taller on one side than the other, so three readings give a true picture. Measure to the surface the door will actually close against, allowing for any raised threshold, tiled step or weather strip at the bottom.
Write down all three heights. The smallest height is again the working figure, because a door made to the tallest reading will catch on the lower side of the head or scrape a raised threshold.
- Measure from the sill to the underside of the head
- Take readings on the left, centre and right
- Allow for a raised threshold or tiled step
- Use the smallest height as your working figure
Step 3: Take the smallest reading, then note the hinge side
With six numbers recorded, the door is sized to the smallest width and the smallest height. This single rule prevents the most common measuring mistake, ordering a door that fits one corner of the opening but fouls another. A few millimetres of clearance is built in by the maker, so you do not subtract anything yourself, you simply supply the true smallest dimensions.
Next, decide the hinge side. Stand outside facing the door and note whether the hinges should be on the left or the right, which usually matches the existing door so it swings the same familiar way and clears furniture, steps and the screen. Getting the hinge side right at order time avoids a door that opens the wrong way for the space.
- Order to the smallest width and smallest height
- Do not subtract clearance yourself; the maker allows for it
- Decide hinge side standing outside facing the door
- Match the existing door's swing where possible
Step 4: Check frame depth, then book a free measure
Finally, check the frame depth, the distance from the front face of the opening to where the door will mount, and look for anything that could interfere, such as a flyscreen, a deadlock, a door closer, a tiled reveal or a narrow porch. Note the wall type too, since fixing into brick, timber or rendered block changes the fasteners used. These details let the installer specify the right frame and fixings the first time.
Because a security door is custom-made to your exact opening, an error of even a few millimetres can mean a door that will not fit. For peace of mind, book a free on-site measure, where the opening, hinge side, frame depth and locking are all confirmed precisely. Call Steve at Shire Security Doors and Screens on 0410 474 256 or email steve@shiredoors.com.au.
- Measure the frame depth front to back
- Note flyscreens, deadlocks, closers and tiled reveals
- Record the wall type for the right fixings
- Book a free professional measure when in doubt
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Frequently asked questions
How do I measure a doorway for a security door?
Measure the width at the top, middle and bottom of the frame, and the height on the left, centre and right, all between the inside faces of the opening. Record every figure in millimetres, then order the door to the smallest width and smallest height so it fits the tightest point of the opening.
Why do I take the smallest measurement?
Door openings are rarely perfectly square, so the three width and three height readings often differ by several millimetres. Ordering to the smallest figure ensures the door clears the tightest part of the frame. A door built to the largest reading would jam against the narrowest point and never close cleanly.
Do I subtract anything for clearance?
No. The manufacturer builds in the necessary fitting tolerance, so you supply the true smallest width and height of the opening without subtracting anything yourself. Subtracting your own allowance on top of theirs is a common cause of doors that end up too small and leave a visible gap.
How do I work out the hinge side?
Stand outside facing the door and note whether the hinges should sit on the left or the right. This usually matches the existing door so the new security door swings the same familiar way and clears furniture, steps and any screen. Confirming the hinge side at order time avoids a door that opens awkwardly.
What is frame depth and why does it matter?
Frame depth is the distance from the front face of the opening to where the door mounts, measured front to back. It affects which frame and fixings suit your opening, especially around deadlocks, closers, tiled reveals and the wall type. Noting it up front lets the installer specify the right frame the first time.
Should I measure myself or get a professional measure?
A security door is custom-made to your exact opening, so even a few millimetres out can mean it will not fit. If you are at all unsure, book a free on-site measure where the opening, hinge side, frame depth and locking are confirmed precisely. Shire Security Doors and Screens measures across the Shire on 0410 474 256.
What tools do I need to measure for a security door?
A steel tape measure, a pen and paper, and ideally a second person to hold the tape steady are all you need. A small spirit level helps you see if the opening is out of square. Always record measurements in millimetres, as that is how custom security doors are manufactured.