Board Thread:General Nerf discussion/@comment-30049823-20190523005157/@comment-30049823-20190524053656

So the regular version holds 5 balls comfortably.

The 20 inch version holds 6⅔ balls. (So an extended flapper should have no trouble holding 7 of them in)

Also, ball pit balls come in different sizes, so you want the 2.5" / 60mm ones (I think; I bought all of mine at thrift stores in unmarked or un-specific boxes, so I'm just eyeballin' them with a ruler and going by the fact that tennis balls are in the 65-68mm range.)