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Units of common measurement vary widely, from
time to time, and place to place. Most units of
measurement started as a reference to a physical
object or concept. The foot was the length of a
man's foot, the inch was the width of a man's
thumb, a furlong was the length of a plowed
furrow in a field, an acre was the amount of land
a man and two oxen could plow in a day, etc. At
first, most measurements were only
approximations, but eventually many country's
governments set each at a specific standard to
make commerce possible and fair. Often, when
people settled new lands, they used the names of
old measurements but set their own standards.
Other times, similar sounding measurement names
in different countries had greatly different
values. Some measurements were derived from other
types of measurements, such as a barrel weight
being the weight of a barrel of flour. Often, the
same measurement had different values depending
on the material being measured, such as a wine
tun and a beer tun, or a hank of wool and a hank
of cotton. These differences made sense to the
people that used them, but they seem odd today.
A Frenchman first defined what he called the
'meter' as one ten millionth of the distance from
the North Pole to the equator along the Prime
Meridian. It was later defined, in a more precise
method, as so many wavelengths of a certain color
of light. A liter was originally defined as a
cubic decimeter, and a kilogram was defined as a
liter of pure water at a specified temperature.
Later, the standard was changed such that a
kilogram mass became the standard and the liter
was derived as the volume of a kilogram of water.
This has caused the liter to become slightly more
than a cubic decimeter.
The International System (SI) was first
proposed in France in the 17th century, but was
not adopted by France until 1795. The system
defined that there was only one standard in each
measurement type and each unit greater or less
was a power of ten. This made conversions between
units much simpler. During the 19th century,
several countries made this system their
standard, but notably not Britain or the US. In
1965 Britain began changing to the metric system
as a condition of membership in the European
Common Market. The US government, recognizing the
problems of international trade, officially made
the metric system its standard in 1975.
Still today, units of common measurements
(non-metric) are used throughout the world. It
would be hard to forget the foot, yard, mile,
quart, gallon, or acre because so many physical
objects were based on them. And for convenience
sake, it will always be easier to say "a
cup" than "two deciliters." It is
easier to envision a mile than a kilometer
because fence rows, city blocks, and farmland
measurements were originally based on the mile.
* Much of our written history still refers to
things in common units. The Bible does not refer
to meters or kilograms, but to cubits and stadia,
or shekels and drachma. Wouldn't it be nice to
know what they were talking about way back then?
Now you can use megaConverter! For a more
complete listing of ancient, foreign, and
obsolete measures, download our
'megaSpreadsheet' of conversions in MS Excel
The area of a circle one mil (.001
inch) in diameter.
A British surveyors measure. 40
square rods. ¼ acre.
The basic unit of area in the metric
system. 10 meters square or 100 square meters.
US Counties are often divided into
townships. A standard township is 6 miles square.
Often times, they were semi-independent entities
within the county government, responsible for
their own road maintenance and taxation. Most
rural counties still refer to a particular plot
of land in terms of the township.
Note: Because of round-off
errors, converting from very large units to very
small units or vice-versa may not be accurate (or
practical). Conversion factors can be found by
converting a quantity of 1 unit to another unit
several steps above or below the first. You may
need to string several conversion factors
together to find the factor from a very large
unit to a very small unit, and then you can use a
calculator with sufficient digits to find your