WA Labor's biggest election promise - a massive expansion of Perth's rail system will cost $2.5 billion and include a $416 million Commonwealth cheque dependent on the generosity of the Turnbull government.

Opposition Leader Mark McGowan, who is ahead in the polls, is adamant he will get the federal cash if elected next month and his flagship project will not have a huge funding hole.

Labor is betting on the Commonwealth funds arguing that because it will dump government's flagship project, the controversial $1.9 billion Perth Freight Link road, that will free up $1.2 billion in federal funds that WA should still get.

Play Video The seat will be a battleground leading up to the March 11 election. The West Australian Video The seat will be a battleground leading up to the March 11 election.

However federal coalition MPs including Major Projects Minister Paul Fletcher and Finance Minister Mathias Cormann both say the money will not simply be reallocated.

"We will get that money out of the Commonwealth because that's what happened in Victoria," said Mr McGowan, referring to Victorian Labor keeping $1.5 billion after it similarly cancelled the previous Liberal government's East-West link.

"I will not be bullied, I will not be intimidated by the federal Liberals."

The Treasurer Mike Nahan said Labor's plan would add at least $1.4 billion to WA's net debt and possibly another $1 billion on top of that due to the "rubbery" figures based on land sales and value capture they could not assume they would get.

The $2.5 billion project would include about 54 per cent of state funds, another 22.7 per cent, or $667 million, from land sales, and 9.1 per cent, or $267 million, from "value capture and developer contributions".

"They have finally released it after seven years and they can't fund it. They can't fund Metronet," Dr Nahan told reporters.

Labor transport spokeswoman Rita Saffioti said she was very confident about getting funds from land sales as Perth was growing and first home owners needed supply.

Play Video Subways, on-road bicycle routes and driverless technology all earmarked for Perth. The West Australian Video Subways, on-road bicycle routes and driverless technology all earmarked for Perth.

Dr Nahan said his government had been running a comprehensive land sales program that had struggled to make $147 million because of a soft post-mining boom WA property market.

"If Labor had submitted their costs to Treasury it would have been rejected," he said.

Metronet will add four new rail lines to the five Perth currently has, including connections between lines that shorten trips and remove the need for travellers to go in and out of the CBD.

Perth's population growth was the highest in Australia during the years of the mining boom, leaping above two million people, increasing the need for more roads and public transport.

The city's growth has been below the national average since 2014, however.

"This will revolutionise transport planning across Perth, we need a transport solution and long-term jobs solution for Western Australia," said Mr McGowan, referring to Labor's claim that building Metronet will create 10,480 jobs.

The costings were assessed and ticked off by former senior public servants Professor David Gilchrist and adjunct professor Michael Wood.

The project would be delivered between 2017-18 to 2022-23.