According to Boeing, a 747200 or 747300 has a carrying volume of
26,600 cubic feet (http://www.boeing.com/news/releases/2000/news_release_000531a.html).
A 747400 has a passenger interior volume of 31,295 cubic feet
(http://www.boeing.com/commercial/747family/pf/pf_facts.html).
A ping pong ball is 3.77 cm, or 1.48 inches, in diameter, according to
(http://www.avalanche.org/~issw/96/art5702.html). We'll conceptualize
each ping pong ball as a cube of 1.48"x1.48"x1.48", or 0.001876 cubic
feet, to account for the empty space between the spherical balls. I
used (http://www.onlineconversion.com/volume.htm) to convert cubic
inches to cubic feet; there are 1,728 cubic inches in a cubic foot.
Divide 26,600 by 0.001876, and you get 14,179,104 ping pong balls that
could fit in a 747200 or 747300.
Since the 26,600 cubic feet number probably does not include the
cockpit, I looked up the cockpit's size. According to
(http://www.747cockpit.com/outside_shell.htm)  yes, there is a Web
page for everything  a 747's cockpit is about 14'x15'x8', or 1,680
cubic feet. That's another 895,522 ping pong balls.
Add 14,179,104 and 895,522 and you get 15,074,626 ping pong balls in a
747.
I hope this answer meets your needs. Please do not hesitate to request
clarification if needed.
Search strategy:
747 airplane cubic feet
://www.google.com/search?sourceid=navclient&q=747+airplane+cubic+feet
ping pong ball diameter
://www.google.com/search?sourceid=navclient&q=ping+pong+ball+diameter
conversions
://www.google.com/search?sourceid=navclient&q=conversions
747 cockpit dimensions
://www.google.com/search?q=747+cockpit+dimensions&hl=en&lr=&ie=ISO88591&safe=off 
Clarification of Answer by
mwalcoffga
on
26 Aug 2002 22:56 PDT
Thank you for the compliment on the answer.
I suppose the answer to your followup question depends on what
exactly you are thinking of. The figure of 26,600 cubic feet refers to
a 747 designed for transporting cargo. Thus, it would be pretty empty
except for the cockpit and equipment. The figure would not include
parts of the plane irrelevant to cargo transportation, such as the
wings, engines, etc.
The 31,295 cubic feet figure for the 747400 refers to the size of the
passenger interior. I guess you would have to take out the seats and
storage bins to reach that volume figure.
If you want to know how many ping pong balls could fit into the plane
without taking out any of the seats or bins, I don't know quite how to
figure that out. Sorry.
