Jetstar will soon charge customers money for using overhead lockers on its aircraft, with prices starting from $23.

The Qantas-owned budget carrier said the move was part of a change in its carry-on model, which included removing its 7kg carry-on weight limit.

It would instead move to a size-based carry-on baggage model and a fee to use the overhead lockers.

From February 2 next year, all Jetstar bookings would include one underseat bag such as a backpack, handbag or laptop.

Those who needed more carry-on baggage would have to pre-purchase what the airline calls Priority Carry-on.

The add-on would allow for a second larger bag for the overhead locker and those passengers would be among the first to board.

Jetstar said the availability of Priority Carry-on would be limited, and charges would start at $23 one-way on selected flights and vary.

For example, Dunedin to Auckland one-way would start at $23, Christchurch to Wellington one-way would be from $28, and Auckland to Brisbane from $34.

"We know that weighing carry-on bags at the gate can be frustrating for our customers and for our crew," Jetstar chief executive Stephanie Tully said.

"To make packing easier we've decided to remove the 7kg weight limit, so from February, the main thing customers will need to think about is the size of their carry-on."

Jetstar also detailed its size limits for underseat and overhead bags.

Underseat bags would have to be up to 40 x 30 x 20cm, and overhead bags with Priority Carry-on would have to be up to 56 x 36 x 23cm.

"By giving customers an underseat bag with the option to add Priority Carry-on, we can make better use of overhead locker space, streamline boarding and help more flights depart on time," Tully said.

"Our new carry-on baggage model provides more choice to customers while helping to keep our fares low. You only pay for what you need - travelling with less means paying less, and you can always add more if you need."

Jetstar said there were no changes to its checked baggage allowance.

It said customers with existing bookings for travel after February 2 next year would be upgraded to include Priority Carry-on at no cost.