The angel who talked with me had a measuring rod of gold to measure the city, its gates and its walls. The city was laid out like a square, as long as it was wide. He measured the city with the rod and found it to be 12,000 stadia in length, and as wide and high as it is long. He measured its wall and it was 144 cubits thick, by man’s measurement, which the angel was using. Revelation 21:15-17

The only measurement of heaven comes from Revelation.
12,000 stadia is approximately 1,400 miles and this description calls the heavenly city a cube—1,400 miles wide, high and long. 1,400 miles is about the distance from Florida to Maine and Florida to the western tip of Texas. Square off that region and you have approximately the size of the “heavenly city.” That does not even include the fully restored earth! The population of the United States is around 303 million and not every corner of Texas and Kansas is nearly fully with people, so that’s LOTS of room.

And since there will be plenty of room. . .you can invite your friends.