I'm afraid the calculations of "conviction" above are incorrect.

Regulation ping-pong balls are 40mm, with a volume of about 2 cubic inches. You can't pack spheres much more efficiently than in a face-centered cubic arrangement, which still leaves about 26% empty space. So each ping-pong ball really needs 2.7 cubic inches. A cubic foot equals 1728 cubic inches, and would hold 640 balls. A Boeing 747 is about 230 feet long and the body diameter is about 20 feet, which works out to a cylindrical volume of roughly 72,000 cubic feet, or 46 million balls. However, the body isn't perfectly cylindrical, and it's not empty. If you still want the plane to fly, you're limited to Boeing's maximum cargo capacity (for a 747 freighter) of about 27,000 cubic feet, or 17 million ping-pong balls.

Regulation ping-pong balls are 40mm, with a volume of about 2 cubic inches. You can't pack spheres much more efficiently than in a face-centered cubic arrangement, which still leaves about 26% empty space. So each ping-pong ball really needs 2.7 cubic inches. A cubic foot equals 1728 cubic inches, and would hold 640 balls. A Boeing 747 is about 230 feet long and the body diameter is about 20 feet, which works out to a cylindrical volume of roughly 72,000 cubic feet, or 46 million balls. However, the body isn't perfectly cylindrical, and it's not empty. If you still want the plane to fly, you're limited to Boeing's maximum cargo capacity (for a 747 freighter) of about 27,000 cubic feet, or 17 million ping-pong balls.