The federal government will pay half the $9 million cost of extensive work on the Parap Leisure and Sports Centre, encompassing changes to the existing pool, construction of a 25-metre pool, a shade structure and other services.

Mr Hockey, conveying information he had been given on the day, told reporters it is "kind of extraordinary" that the pool is 49.5 metres and the government would help bring it to Olympic standards.

His comments at the Darwin pool left locals concerned that they had unwittingly been short-changed for many years.

But it soon became clear that the pool's problem is that it is in fact too big.

A spokesperson for the City of Darwin later told Fairfax Media that the pool, opened in 1960, is about 30 centimetres longer than it should be, not 50 centimetres shorter.

It is 55-yards long, the standard size of competitive swimming pools in the era of imperial measurements. This means that it is approximately 50.3 metres long, according to the City of Darwin.

Mr Hockey made the announcement in the marginal seat of Solomon with the local member Natasha Griggs, who has held the seat since 2010, and Assistant Employment Minister Luke Hartsuyker.

"I'm very pleased to be here with Natasha and the elected representatives of City of Darwin to make a 50-metre pool, 50 metres," the Treasurer said on Wednesday.

"It's kind of extraordinary that it's 49.5 metres but of course, being a capital city you should have an Olympic approved pool, and that means that your swimmers have the chance to compete with the rest of the world."

While in Darwin, Mr Hockey also addressed the local chamber of commerce and local radio.

Commonwealth funding is being drawn from the Coalition's $1 billion National Stronger Regions Fund, which is set aside for "priority infrastructure" in regional communities.

The program begins in 2015-16 and will run five years. Grants are worth $20,000 and $10 million.

The Northern Territory government will share the cost of the pool project with the Commonwealth.

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