How to measure your garage door opening (with diagram)

To measure a garage door opening you need 5 figures: the opening width, the opening height, the headroom above the opening, the side room on each side, and the backroom (depth into the garage). Measure the width and height of the actual opening, not the old door, and always in millimetres. Getting these right before you order avoids the single most expensive mistake in a new garage door: a door that will not physically fit the opening or clearances.

The 5 measurements you need

Work through these in order and write each one down in millimetres.

1. Opening width: the clear horizontal gap, measured at the top, middle and bottom. Use the smallest.
2. Opening height: the clear vertical gap from floor to the underside of the top of the opening.
3. Headroom: the space from the top of the opening up to the ceiling or nearest obstruction. This decides whether a standard, low-headroom or roller track will fit.
4. Side room: the space from each side of the opening to the nearest wall or obstruction. Sectional and roller doors both need room for tracks or the drum.
5. Backroom: the depth from the opening back into the garage, needed for sectional door tracks.

The full garage door types guide explains why each clearance matters for each door format.

Typical clearances by door type

Use this as a rough guide to what your measurements need to allow.

Door type	Headroom needed	Side room needed
Roller	200mm to 400mm	60mm to 100mm each side
Sectional (standard)	300mm to 400mm	90mm to 120mm each side
Sectional (low headroom)	100mm to 200mm	90mm to 120mm each side
Tilt	High, plus front clearance	Moderate

If your headroom is very tight, a roller door or a low-headroom sectional kit is usually the answer. Confirm the exact requirement with a specialist, and check pricing on the cost page.

Common measuring mistakes

• Measuring the old door, not the opening: the door is smaller than the opening it covers. Always measure the structural opening.
• Measuring in only one spot: openings are rarely perfectly square, so measure width and height in 3 places and use the smallest.
• Forgetting obstructions: light fittings, pipes, beams and storage shelves all eat into headroom and side room.
• Ignoring floor slope: a sloping garage floor changes the effective height across the opening.
• Using inches or rounding: order in millimetres and do not round, since a few millimetres can matter for a tight fit.

If you are also deciding on size, our single vs double garage door guide covers the trade-offs, and the garage door replacement cost calculator prices your dimensions.

Standard Adelaide opening sizes

Most Adelaide garages fall near a few common sizes, though yours may vary, especially in older eastern-suburb homes where openings were bricked to no standard at all.

• Single: roughly 2,400mm to 2,700mm wide, 2,100mm to 2,400mm high.
• Double: roughly 4,800mm to 5,200mm wide, 2,100mm to 2,400mm high.

Newer estate homes in Angle Vale, Golden Grove and Mawson Lakes tend to be more consistent; heritage and character homes in Norwood and Unley are the least standard and most worth a professional measure.

Frequently asked questions

Should I measure the door or the opening?

Always the opening. The door overlaps the opening, so it is larger than the clear gap. Ordering to the door size gives you a door that is too small.

What if my garage floor slopes?

A sloping floor changes the height across the opening, so measure the height at both sides and note the difference. A specialist accounts for slope when fitting seals so the door closes evenly.

Do I really need to measure headroom and side room?

Yes. These clearances decide which door types will physically fit. Too little headroom rules out a standard sectional door but not a roller or low-headroom kit. Skipping them is how the wrong door gets ordered.

Would rather have it measured for you? Get matched with vetted Adelaide specialists free for an accurate on-site measure and quote.