The post-Christmas boom is hitting charity stores as many Aussies turn their annual clean-out into generous donations.

The St Vincent de Paul Society warehouse in Mitchell in Canberra's north expects to receive between 75,000 to 100,000 kilograms of donations in January alone.

While at the Salvation Army Fyshwick store there is a constant stream of cars for eight hours each day, with donations coming in faster than volunteers and employees can sort them.

"We have tonnes of donations come through all the stores," ACT and Monaro area manager Tony O'Connell said.

"I put extra drivers and extra staff on to try to cover that."

But with Christmas gifts often replacing older items, charities are asking people to think about what they are dropping off.

What can be donated?

Charites say only items in good condition should be donated. ( 666 ABC Canberra: Hannah Walmsley )

The stores are looking for items that are in good condition.

"Something you would give to your friend, we would take as a quality donation," St Vincent de Paul Mitchell warehouse manager Gary Crowder said.

Larger stores can take furniture, although smaller items are better for storage and donation.

The Mitchell warehouse donates 80 per cent of its furniture to people in need, and Mr Crowder asked people to remember that when donating.

"You'd want to see something you might be proud of to put in your home," he said.

"Because we're trying to give their dignity back by supplying them with items that they could be potentially proud of."

Big ticket items are unwanted Christmas presents, while stores are also looking for good quality clothing, manchester and children's toys.

What cannot be donated?

Do not leave donations next to the bins. ( 891 ABC Adelaide: Spence Denny )

Anything broken, ripped or dirty cannot be sold.

"We just don't have the resources to clean or repair items," Mr Crowder said.

Charity stores also warn against leaving items outside full donation bins, with most having to be thrown out.

Vinnies volunteer Mandy Conway loves sorting through donations with the other workers, but said the festive period brought a lot of unusable items.

"We get a lot of unwanted Christmas presents, if I can say that, which is wonderful because they're the big ticket items," she said.

"But people sometimes donate the replacement item, which doesn't have a lid or is cracked or has been in the backyard."

What to keep in mind

Soiled mattresses will not be accepted. ( Supplied: NARCO.org.au )

Not all stores have the resources to employ an electrician to test and tag electrical goods.

In addition, some stores cannot accept anything that is governed by safety standards, including prams, cots and baby seats.

Mattresses in good condition can be accepted by some places but soiled ones will likely be rejected.

What should you do with items not suitable for donation?

The Green Shed will sometimes take broken or unusable items. ( 666 ABC Canberra: Hannah Walmsley )

The Green Shed, which is contracted by the ACT Government, can accept broken or unusable items to sell for spare parts or new uses.

Mattresses in poor condition can be recycled for a cost of $33 if dropped off at ACT tips, or $29.50 if collected.

The Soft Landing program recycles 90 per cent of the mattress and turns them into boxing bags, gloves and carpet underlay.

Old televisions and computers are accepted by the tip for free under the National Television and Computer Recycling Scheme.

While mobile phones can be dropped off at Australian Post shops for recycling by Mobile Muster.