How many believers were there at the time of the ascension?

There were 120 believers after the ascension.

The number of names together were about an hundred and twenty. Acts 1:15

There were more than 500 believers before the ascension.

He was seen of above five hundred brethren at once; of whom the greater part remain unto this present, but some are fallen asleep. 1 Corinthians 15:6