The provisional results of Nigeria's first census in 15 years show that Africa's most populous nation has a population of more than 140 million
The National Population Commission said this was an increase of 63% since 1991.
The headcount is sensitive, as funding and political representation for Nigeria's states depend on the results.
Previous results have been mired in controversy and allegations of fraud, but March's census left out questions on religion and ethnicity.
The government was concerned that such information would trigger ethnic riots.
The National Population Commission (NPC) chairman said this time he felt there would be no problems.
"I don't expect any controversy because we have done a transparent and credible census. We have done it as honestly as we can, using the most scientific methods of census taking," Sumaila Makama told the BBC's Focus on Africa programme.
The BBC's Mannir Dan Ali in the capital, Abuja, says the big surprise in the results so far is that Nigeria has three million more men than women.
The last census put Nigeria's population at about 88.5m.
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