How much garage door do you need in Cranbourne? Size the opening, the springs and the motor with a tape
Measure the opening, never the old door. A standard Casey double opening is 4,800mm by 2,100mm, which is 10.1 m² of door. That needs an opener rated above 10 m², meaning an 800 newton unit at the very least and a 1000 newton unit once the panels are insulated, and it needs 25,000-cycle springs if your household opens the door more than about five times a day. A standard single is 2,400mm by 2,100mm, or 5.0 m², and a 600 newton opener covers it comfortably.
Garage door sizing estimator
Slide your opening area and your daily usage, choose the door and the counterbalance, and the estimator sizes the job and gives a 2026 Cranbourne range. If you want line-item rates rather than a total, they are on the pricing page.
What the estimator assumes
- A swap into an existing, sound opening in the City of Casey, with reasonable driveway access for a van and trailer.
- New springs and new tracks, not reused hardware, plus photoelectric safety beams, auto-reverse and a manual release set up at handover.
- Two remotes and a wall control on any option that includes a new opener.
- A stock Colorbond colour unless you tick the non-stock box. Special orders add 2 to 4 weeks.
- It excludes structural work: rebuilding a rotted jamb, repairing a cracked lintel or widening the opening.
- It is a 2026 guide only. A fixed price needs a measure of the six numbers below.
How to measure it properly, with a tape and a phone
Ten minutes, one tape and one other person to hold the end. The single most common mistake is measuring the old door instead of the opening, which gives you a door 20 to 40mm too small and a permanent draught gap at the sides.
- Width, three times. Brick reveal to brick reveal at the top, at the middle and at the bottom of the opening. Write all three down. Use the smallest.
- Height, three times. Slab to the underside of the lintel at the left, the centre and the right. Use the smallest again. On an older Cranbourne slab the difference between left and right is often 10 to 20mm, and that gap is the whole reason for measuring three times.
- Headroom. From the top of the opening straight up to the lowest thing above it: the ceiling, a beam, a light, a pipe. Write down what the obstruction actually is.
- Side room. From each side of the opening out to the nearest wall, meter box, shelf bracket or downpipe. Measure both sides, they are rarely the same.
- Backroom. From the opening straight back to the first ceiling obstruction. This is where the rail and the motor head live.
- Power. Distance from where the motor head will hang to the nearest 10 amp power point, and whether it is a double or single outlet.
Then take five photos on your phone and text them with the numbers: the whole opening from about three metres back, each top corner from inside, the ceiling above the opening looking back, and the existing motor head plate if there is one. That is enough for us to quote accurately without a visit in most cases, though the free measure is still the safer path.
Rules of thumb and the allowances to add
| What you are checking | Sectional door needs | Roller door needs | If you do not have it |
|---|---|---|---|
| Headroom above the opening | 300 to 400mm for standard lift | 300 to 400mm for the barrel | Low-headroom track kit, down to about 150 to 180mm, adds $220 to $480 |
| Side room, each side | 100 to 130mm of clear wall | 75 to 100mm | Reduced side-room brackets, or the opening has to be reworked |
| Backroom from the opening | Door height plus 500 to 800mm for the rail and motor | Around 300mm, the curtain rolls up at the opening | Roller becomes the better answer, or a jackshaft-style drive |
| Width tolerance | Within about 50mm of a stock size, packed out on site | Same | Made to measure, adds $300 to $900 and a week or two |
| Power for the opener | 10 amp outlet within about 1.5m of the motor head | Same | Licensed electrician and a Certificate of Electrical Safety, $280 to $550 |
Two allowances people forget. First, always order to the smallest of your three measurements and let the installer pack the difference: a door 15mm under is invisible, a door 15mm over does not go in. Second, allow for what is going to live on that ceiling later. Half the garages in the newer Casey estates end up with a storage platform or a roof-rack hoist over the door line within two years, and that eats the backroom the rail needs.
Rather we measured it?
Free on-site measure within 48 hours across the inner Casey ring, and a fixed written quote off the back of it. Or text us the six numbers and we will size it from those.
How much motor, and how much spring
Match the opener to the door area, not to the price
Every opener has two numbers on its plate: a force in newtons and a maximum door area in square metres. The area is the one that matters. As a rough guide a 600N unit is typically rated to about 8 to 9 m², an 800N unit to about 12 to 14 m², and 1000N and above beyond 16 m². Your 10.1 m² double is therefore beyond a 600N unit, fine on an 800N with a light single-skin door, and wants a 1000N once the panels are insulated.
Weight is what sits behind those ratings. A single-skin roller curtain on a double opening is roughly 55 to 80kg, an uninsulated steel sectional 75 to 110kg, a 40mm foam-core insulated sectional 110 to 160kg, and an aluminium timber-look composite 150 to 200kg or more. Same opening, three times the weight. That is the reason a like-for-like opener swap sometimes is not like-for-like at all, and it is covered on the motor swap page and under motor replacement.
Size the springs off your actual usage
One cycle is one open plus one close. Count honestly for a week: two adults leaving and returning is four, a school run is two more, and a teenage driver or a home business adds two to four. Then do the arithmetic:
- 4 cycles a day is 1,460 a year, so 10,000-cycle springs last about 6.8 years.
- 6 cycles a day is 2,190 a year, so 10,000-cycle springs last about 4.6 years, and 25,000-cycle springs about 11.4 years.
- 10 cycles a day is 3,650 a year, so 10,000-cycle springs last under 3 years, and even 25,000-cycle springs are only good for about 6.8.
The upgrade costs $120 to $260 at install. A spring replacement later costs $380 to $680 for the pair plus a $120 to $180 call-out. Anyone at six cycles a day or above should take the upgraded springs, and it is not a close call.
The sizing mistake that costs the most around here
Undersizing the counterbalance and the opener on a heavy door, on a household that uses it constantly. It is the classic builder specification across the Casey growth corridor: a 10 m² double, 10,000-cycle springs and a 600N opener working above its rated area from the day the keys were handed over. Nothing is technically broken at handover, and everything is on a five-year fuse.
The second most expensive one is measuring the old door rather than the opening, which turns up as a 20 to 40mm gap down one side that no seal will ever properly close. Third is forgetting the ceiling: ordering a standard lift sectional for an opening that has a beam or a storage platform 250mm above it, then paying for a low-headroom kit as a variation on the day. All three are avoided by six measurements and ten minutes.
Worked example: a 2014 double-storey in Cranbourne East
Opening measured at 4,810mm, 4,805mm and 4,800mm wide, and 2,105mm, 2,100mm and 2,100mm high. We order to the smallest, so 4,800 by 2,100, which is 10.08 m². Headroom 380mm, so standard lift is fine and no low-headroom kit is needed. Side room 140mm on the left and 115mm on the right, both adequate. Backroom 2,900mm, comfortably more than the 2,100mm door height plus 800mm. Power point sits 3.2 metres from where the motor head will hang, so a new outlet is needed. The household runs 7 cycles a day, which is 2,555 a year, so 10,000-cycle springs would be finished in under four years.
The specification and what it actually came to:
- 40mm foam-core insulated Colorbond sectional, 4,800 by 2,100, stock colour, tracks and install: $2,850
- 1000N quiet belt-drive with battery backup, two remotes and a wall control: $1,180
- Upgrade to 25,000-cycle torsion springs: $190
- Remove and take away the old door: $260
- Full weather seal kit, bottom, sides and head: $290
- New 10 amp outlet by a licensed electrician, with the Certificate of Electrical Safety: $380
Total: $5,150 including GST. The estimator above, set to 10 m², insulated sectional, 25,000-cycle springs, a 1000N opener and those three extras, returns $4,800 to $8,500, and this job sat near the bottom of that band because the opening was square, the access was good and the colour was stock. Openings that have racked, or that need a low-headroom kit and a non-stock colour, land in the upper half.
When you do not need to size anything at all
If the door and the tracks are sound and only the opener has died, none of this applies. The new opener has to be rated for the existing door area, and that is the only number you need. A straight motor swap is 90 minutes and $580 to $1,400. Start at why the door will not open.
And a genuine constraint on the upsell: if your opening is a standard 4,800 by 2,100, the garage is detached, unheated and used for cars and a mower, the extra $900 to $1,400 for a foam-core door buys you very little. Buy the single-skin door, take the 25,000-cycle springs and the correctly rated opener, and put the rest in your pocket. Likewise, if your existing opener is under about eight years old, quiet, has a working auto-reverse and is rated above the new door’s area, keep it and save $700 to $1,400. We will check the plate and tell you either way at the measure.
What we will not do is fit a door to an opening that is not sound. If the jamb is rotted, the lintel is cracked or the opening needs widening, that is a carpenter or builder job with a building permit attached, and we will say so before you order anything. If you are still deciding what to buy, read choosing a garage door material, the budget tiers and sectional versus roller first, and what happens on install day once you have chosen.
Sizing questions we get asked
What is the standard garage door size in Australia?
How do I measure a garage door opening properly?
How much headroom does a garage door need?
How powerful does my garage door opener need to be?
How many spring cycles do I need?
How heavy is a double garage door?
Send us your six numbers and we will size the job
Text or email the measurements and we will confirm the door size, the spring rating and the opener you need, with a fixed price, within one business day.
Get the size right the first time
Free measures across Cranbourne, Berwick, Narre Warren, Hampton Park and Endeavour Hills. Same-day phone advice if you just want a sanity check on your numbers.