Treasury costings of WA Liberal promises have shown the party's estimates are reasonable.

The Liberals have made more than $2.8 billion in promises, including the controversial Perth Freight Link project.

"The estimates have been based on a sound information set and methodologies," WA's Under-Treasurer Michael Barnes said on Wednesday.

Premier Colin Barnett said earlier on Wednesday he was confident the pledges would be roughly on the money.

"We have taken great care in 70 different policy areas to indicate what we believe the cost of each will be ... totally contingent on Western Power being sold," Mr Barnett told reporters.

"That is in sharp, sharp contrast to the Labor party."

Mr Barnett earlier lashed Labor for not subjecting $5 billion worth of promises, including $2.5 billion for its flagship Metronet rail project, to the same scrutiny.

Rather than hand Treasury its costings details, Labor has enlisted two former senior public servants, including former Public Sector Commissioner Mike Wood, to run the ruler over its numbers.

Labor has questioned the independence of Treasury, accusing the Liberals of planting a stooge in its briefing with the government department ahead of the 2013 state election.

Mr Barnett recently claimed Mr Wood had a close connection to former Labor premier Brian Burke, who was jailed for rorting travel expenses.

WA Labor leader Mark McGowan said he was confident the release of the party's costings on Thursday would rebut Barnett government suggestions they "don't add up".

- AAP

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Liberal costings for $2.8 billion worth of projects reasonable, says Treasury - WAtoday