Charles Ellicott Commentary Acts 1:15

"And in these days Peter stood up in the midst of the brethren, and said (and there was a multitude of persons [gathered] together, about a hundred and twenty)," — Acts 1:15 (ASV)

The number of names together were about an hundred and twenty.—The number probably included the Seventy of Luke 10:1, perhaps also Joseph of Arimathæa and Nicodemus, and some of the “five hundred” who had seen their risen Lord in Galilee or elsewhere (1 Corinthians 15:6). The use of “names” may be merely as a synonym for “persons,” but it suggests the idea of there having been a list from which St. Luke extracted those that seemed most conspicuous.