LENGTH

American                        Imperial            Metric
1 football field                120.000 yds1        109.728 m
to the moon 1 time              238,855 mi          384,400 km
to the moon and back2 1 time    477,710 mi          768,800 km
around the earth3 1 time        24,901.6 mi         40,075 km
1 statue of liberty4            50.7220 yds         46.3800 m

AREA

American                        Imperial            Metric
1 football field5               1.32200 ac          0.53500 ha

VOLUME

American                        Imperial            Metric
1 grand canyon                  1.51014E12 cu yds   1.15458E12 cu m

Usage and Synthesis

Specialized fields may combine units in order to describe the various measurements they require. For example, astronomers have coined the length unit "light-year", defined as the distance which light may travel in a year through a vacuum:

1 light-year = 9.5E15 meters

Similarly, Americans (especially those engaged in marketing work) will also synthesize units, using other Metric/Imperial/American units or even their own products as building blocks. Kraft Foods, for example, notes that "one year's production of Cool Whip will fill the Grand Canyon". Thus, we may synthesize a unit of volume:

1 coolwhip-year = 1 Grand Canyon

It is also worth noting that most Americans have no real understanding of some of these units, with the notable exception of the football field. One might just as well substitute "really, really tall" for "three statues of liberty", or "a whole damn lot" for "enough to go to the moon and back thirty-seven times". This, of course, is why these units are used.


Notes

1) A football field is sometimes equated to 100 yards; this ignores the end zones, and is therefore not canonical.

2) There is no discernible reason that a doubling of a unit might be used, except perhaps to convey a stronger impression of the scale. Paradoxically, this doubling of the unit halves the magnitude used to express the distance, which one would expect to diminish its impressiveness to the audience. Go figure.

3) This is sometimes given as around the Equator, which is on the whole more accurate but perhaps less impactful.

4) Use of the Statue of Liberty as a unit of measure seems odd, given that most people with whom I've spoken have been surprised at the actual size of the Statue of Liberty. Most, myself included, had a vague notion that it was considerably larger than it actually is.

5) The football field is an interesting unit, being used as a measure of both area and of distance. This may confuse non-native speakers, but the explanation is simple. A standard football field is a rectangular plot of land on which the sport is played by two opposing teams. Hence the field serves naturally as a unit of area. However, the objective of the sport is to move the ball along the length of the field; lateral motion is inconsequential to the game's state, and thus the primary focus of the sport is actually linear. Therefore, the field's length becomes itself a useful unit of measure. Note that here I have used the canonical 120-yard football field, end zones included, in calculating area conversions.


Sources:
http://seds.lpl.arizona.edu/nineplanets/nineplanets/luna.html
http://geography.about.com/library/faq/blqzcircumference.htm
http://www.teachingcompany.com/cp19798/INVWood.html
http://www.kraftunitops.com/fun_facts.html
http://www.energizer.com/bunny/balloonfacts.asp
http://www.nrdc.org/land/use/fminef.asp
http://www.uncwil.edu/nurc/kids_page/subsea_facts_answers.html
http://www.onlineconversion.com

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