The Premier Colin Barnett has defended a discrepancy in cost estimates on relocating the new stadium, saying he gave a ball-park figure in an interview on FM radio.

Colin Barnett told NOVA FM that if the new stadium site in Burswood was to be relocated, somewhere in the order of $100 million would be lost.

The Premier had previously been quoted as saying it would cost only $20 million.

Mr Barnett has defended the $80 million discrepancy, telling ABC local radio the newspaper which reported it needs to "lighten-up."

"I don't think the listeners out there want me to say 'I can't answer that, I've got to go talk to treasury,'" he said.

Program host Geoff Hutchison responded to the comment when he said listeners wanted the Premier to tell the truth.

"I do tell the truth, I always tell the truth," Mr Barnett said.

Shadow Treasurer Ben Wyatt said the Premier needed to explain the cost.

"Where is this money coming from? Where is it being spent?" he asked.

"Why do taxpayers have to look at other places beyond the budget to find out how Colin Barnett is spending money on the stadium?"

The Premier says additional costs would be added to the project if Labor was to move the stadium to Subiaco.

Mr Barnett says the overall cost would be higher because it would cause a two year delay and have to factor in the removal of homes and realignment of roads.