City are top of the table at Christmas, two points ahead of nearest rivals Manchester United after collecting an impressive 44 points from 17 games.
Sir Alex Ferguson's men clinched the title last season with 80 points, but Mancini reckons his side would need to beat it by 10 for the trophy to end up at Eastlands in May next year.
"If we want to win the title we should get 90 points because United keep winning," he was quoted as saying in The Sun newspaper.
"I'm happy we're top of the table at Christmas but as I've said many times, it is important to stay there for the rest of the season.
"For this, it is difficult. United continue to win as do Arsenal and Tottenham.
"But it is better to stay on top than be second."
Mancini has virtually accepted defeat in his bid to keep the Toure brothers in England beyond the FA Cup third-round tie with Manchester United on January 8.
Mancini has often spoken of his concern at how his side would cope without Kolo and, in particular, Yaya, who are required for the Ivory Coast's African Nations Cup campaign.
Initially, the City chief expressed the hope that their departure could be delayed until after the Premier League encounter with Wigan at the DW Stadium on January 16.
That now appears unlikely, with the pair now also set to miss the Carling Cup semi-final first-leg against Liverpool on January 11.
"It is difficult but I think they will leave us after United," said Mancini.
"We have talked with their manager three days ago and will talk again with the Ivory Coast president.
"We will try but it is difficult."
Instead, there is the potential for bringing in additional reinforcements.
Cash is available for transfers but with UEFA's Financial Fair Play demands to be met, Mancini knows he will have to sell before he can buy.
"We should sell some of our players before we do anything," he said.
"After that maybe we can do something but at the moment there is nothing."