Windows and doors are the leftovers people feel silly about. A stack of tiles you can explain away. A brand-new sliding door standing in the corner of the garage is harder to ignore, because everyone who walks past knows roughly what it cost.
They pile up for ordinary reasons. Big jobs get over-ordered so the site never stops waiting on a supplier. A window comes in the wrong size and the right one gets ordered before anyone deals with the first. A client changes the plan halfway through. A display home gets cleared out. And every renovation that touches an external wall strips out doors and windows that were doing their job fine until the layout changed.
None of that is a mistake worth beating yourself up over. The mistake is letting good gear sit until it warps, gets a corner knocked off, or ends up in a skip because you needed the space.
First, work out which pile it's in
There are really two kinds of leftover here, and they sell to different people.
New or near-new surplus is the over-order, the ex-display unit, the wrong-size delivery that never got installed. Frames are square, glass is clean, seals are intact, hardware is all there. This is the stuff that moves, because the next buyer is getting something close to what they'd pay full price for at a merchant.
Salvaged is what comes out of a reno. It has been in a wall, so it has a few marks and maybe some old paint or silicone on the frame. Timber doors in particular salvage well .. solid-core and older hardwood doors get bought for character jobs and second dwellings all the time. Aluminium windows salvage too, as long as the glass is sound and the frame isn't bent.
Both piles are worth something. Just be honest about which one you're holding, because that's what sets the price and the words you use to sell it.
What actually holds its value
Standard sizes move faster than odd ones. A common sliding window or a standard door blank suits more jobs than a one-off custom unit, so it sells quicker.
Common colours help. A frame in a colour that half the street already has is easier to match into someone else's job than a bold one-off.
Glass intact is the whole thing. A cracked pane or a blown double-glazed seal drops the value hard, because reglazing eats the saving. Say so plainly if it's there .. a buyer will find it anyway.
Hardware present matters more than people think. Handles, locks, rollers, the striker plates. A door with all its furniture is a door someone can hang. A door missing bits is a project.
For anything new, keep the labels. Energy rating stickers, compliance marks and the sizing label on the glass all tell a buyer exactly what they're getting without a site visit. That's the difference between a quick sale and twenty questions.
Measure it once, properly
Whoever buys it is going to ask the same handful of things, so put them in the listing and save yourself the back and forth. Width and height of the frame, and the depth if it's a window, because that has to suit the wall. The frame material. Whether the glass is single or double glazed. For a door, the handing .. which way it opens .. and whether it's a slab only or hung in a frame.
Take the photos in daylight, from the front, and get one close-up of any damage. A leftover window shot honestly in the sun sells. The same window shot in a dark shed at night looks like junk, even when it isn't.
Where it can go
Sometimes the supplier will take a standard unit back, though anything custom or cut usually can't be returned once it's made. Worth a phone call before you assume.
Other trades are the quiet market. The chippie two jobs over might need exactly the door you're sitting on. A message in a local trade group moves more of this stuff than people realise.
Salvage and architectural reuse yards take doors and windows, especially older timber. Some charities and community reuse projects take them too, if you'd rather it just go to good use.
And if you'd rather not chase it around, this is the sort of thing Overrun is built for. It's an Australian marketplace for surplus building materials and nothing else, so the people looking are looking for building gear, not scrolling past it. You list what you've got in about a minute from your phone, someone local finds it because they searched for it, and they collect and pay you directly. We never take a commission on the sale.
Storing it so it's still worth selling
If it's not going straight away, store it properly or you'll lose the value while it waits. Keep windows upright, not flat, so the glass isn't taking weight across the pane. Keep doors flat and supported, or standing dead upright, so they don't bow. Get all of it off the ground and out of the weather. Aluminium copes with a lot, but timber will swell, and a swollen door is a firewood door.
The skip should be the last resort here, not the default. Glass and framing are heavy and awkward, they fill a bin fast, and you paid for the unit once already. Sorting the good ones out before you book the skip takes ten minutes and usually pays for itself.
Quick answers
Can I sell second-hand windows and doors in Australia? Yes. New surplus and salvaged units both sell, as long as the glass is sound and the frame is straight. Standard sizes and common colours move fastest. Be upfront about any damage and include full measurements.
What measurements do buyers want? Frame width and height, and the depth for a window. Note the frame material, whether the glass is single or double glazed, and for a door the handing and whether it's a slab or hung in a frame.
Is it worth keeping leftover doors or should I just skip them? Keep the good ones. Doors and windows are heavy and bulky, so they fill a skip you've paid for while you throw away something you also paid for. Store them properly and sell or pass them on instead.