“Belgiums” are also used to measure unearthly objects…
“A one kilometre asteroid striking the Earth at a typical speed of 25 to 30 kilometres per second would have a devastating effect. On impact the enormous kinetic energy of the body will instantaneously be dumped into target rock in an explosion equivalent to 300,000 megatons of TNT – the largest man-made nuclear weapon had a yield of 60 megatons. Flash and blast from the impact will destroy an area the size of Belgium.” http://www.thekeyboard.org.uk/Earth%20impact.htm
“In 1908 an asteroid explosion over Siberia visited ruin on an area the size of Belgium.” http://www.amazon.com/exec/obidos/tg/detail/-/0306457512/104-1493818-5772714?v=glance
And some more arithmetic …
…Luxembourg x 7 = Belgium
“Seven rocks the size of Luxemburg would probably do just as much damage as one the size of Belgium.” http://www.embl-heidelberg.de/ExternalInfo/oipa/n2003/n13/n13_11.html