THE number of Australians missing from the electoral roll is rapidly approaching the population of Perth, the Australian Electoral Commission says.

The commission says 1.5 million voters are absent - including one in two 18-to 19-year olds - and the problem is growing.

Underenrolment is most common in the 18 to 39 age group. The largest number of potential voters are missing from NSW (475,800) and Victoria (327,600). In the Northern Territory, an average of 16,550 people are missing per electorate, compared with 9900 per electorate in NSW.

The Electoral commissioner Ed Killesteyn told the Herald the number of missing voters had grown from 1.2 million in 2009 to 1.5 million this year, outstripping population growth.

Accepted wisdom traditionally held that 5 per cent of Australians do not vote. But this grew to 8 per cent last decade, and about 10 per cent this year, Mr Killesteyn said.