Allardyce described the England forward as an "all-round footballer" and said that the deal will be beneficial to all of the parties involved.
"I think for all parties this is a great signing," BBC Sport quotes him as saying.
"Andy is an all-round footballer, but because he is 6ft 3in and one of his strengths is his aerial power, everybody dismisses the ability he possesses on the floor.
"Hopefully he can score goals for us and we will be in a very good position at the end of the year in the Premier League."
Carroll could make his West Ham debut during Saturday's home encounter against Fulham.