Garage door guides
How to measure your garage for a new door
Measuring a UK garage door needs three figures: the structural opening (the full brickwork gap), the drive-through width (the usable clear width once the frame is fitted), and headroom above the opening for the operating gear. Getting the structural opening confused with the drive-through width is the single most common measuring mistake and can lead to ordering the wrong size door.
Accurate measuring is where a large share of garage door ordering mistakes happen, and most of them come from confusing similar-sounding measurements rather than from using the tape measure wrong. This guide sets out exactly what to measure and in what order.
Structural opening vs drive-through width
The structural opening is the full width and height of the brickwork or masonry gap before any frame is fitted — this is the number a builder or architect would use. The drive-through width (sometimes called the clear opening) is the usable width once the door's fixing frame is installed inside that structural opening, which is always somewhat narrower because the frame itself takes up space on both sides. Confusing these two is the most common mistake reported when ordering garage doors, because the drive-through figure — the one that actually matters for whether a car fits through — is smaller than the structural opening by the width of the frame on each side.
The reference opening used across this site's pricing, 2290mm × 2250mm, is a structural opening figure for a standard UK single garage.
Step-by-step: what to measure
- Structural width — measure the full width of the brickwork opening at three heights (top, middle, bottom), and use the smallest figure, since openings are rarely perfectly square in older garages.
- Structural height — measure from the floor to the underside of the lintel at both the left and right sides, again using the smaller figure if they differ.
- Headroom — measure from the underside of the lintel up to the ceiling or first obstruction (roof timbers, a beam, pipework). This space is needed for the door's tracks and, for retractable or canopy up-and-over gear, the spring mechanism at the head of the frame.
- Side room — measure the depth of clear wall available on each side of the opening, needed for the vertical tracks on a sectional door or the side gear on a retractable up-and-over door.
- Floor level and slope — check whether the garage floor slopes toward the opening (common for drainage) as this can affect the door's fit and seal at the base.
Common measuring mistakes
| Mistake | Why it matters |
|---|---|
| Quoting structural opening as if it were drive-through width | The ordered door will effectively be narrower to drive through than expected once the frame is fitted |
| Measuring at one height/point only | Older openings are frequently out of square; a single measurement misses the true minimum |
| Ignoring headroom for the gear type | Insufficient headroom can rule out certain gear or operator configurations entirely |
| Forgetting side room needed for tracks | A door can be the right width but still not fit if there isn't enough side wall depth for the track mechanism |
| Not checking floor slope | Can affect the door's seal and clearance at the base, especially on insulated doors |
When to get a professional measure instead
For anything other than a straightforward like-for-like replacement — a new build, an unusual opening shape, very limited headroom or side room, or where automation is planned — a professional survey measure is worth having before ordering, since an installer will check headroom and side room requirements against the specific door and gear being quoted, not just the opening size. Most UK installers include a measuring visit as part of the quotation process for exactly this reason.
Questions people ask
- What is the difference between structural opening and drive-through width?
- The structural opening is the full brickwork gap before any frame is fitted; the drive-through width is the smaller usable clear width once the door's frame is installed inside it. Always confirm which figure a supplier is quoting to avoid ordering a door that ends up narrower to drive through than expected.
- How much headroom does a garage door actually need?
- Headroom requirements vary by door type and gear — up-and-over doors need clearance for the spring mechanism at the head of the frame, and sectional doors need room for the track curve — so the exact figure should be confirmed against the specific product being ordered rather than assumed.
- Do I need side room for a roller garage door?
- Roller doors need side room for their guide tracks and, at the top, headroom or a box for the wound curtain and barrel, though generally less side depth than a sectional door's vertical track system requires.
- Should I measure myself or wait for the installer's survey?
- A rough self-measure is useful for early budgeting and comparing quotes, but for the final order most UK installers carry out their own survey measure to confirm structural opening, headroom and side room against the specific product being fitted, which is the figure that should be used to place the order.
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