Mass & Weight megaConverter #1
INFORMATION
PAGE
Introduction and
Overview
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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! This megaConverter
is specifically for mass and weight measurements
commonly used today in the US, Britain, and by
the SI system. See megaConverters Ancient Weight
#40 and Foreign Weight #41 for conversions common
in ancient times and foreign countries. For a
more complete listing of ancient, foreign, and
obsolete measures, download our
'megaSpreadsheet' of conversions in MS Excel
format.
For the most comprehensive treatment of
measurements, find "NTC's Encyclopedia of
International Weights & Measures" by
William D. Johnstone at your local library.
Glossary
of Conversions:
Avoirdupois is the weight
system for commerce, Troy for
precious metals, and Apothecaries
for druggists.
grain
The grain was the basic weight of the
British and US systems. It was the weight of a
kernel of grain, probably barley.
scruple
The scruple was a small pointed stone used as a
weight standard by druggists.
carat
The carat was the weight of a carob seed. A Troy
measurement used in the weight of precious
metals. A carat is also used to define the
proportion of gold in alloy, 24 carats being pure
gold.
pennyweight
A pennyweight was the weight of an old British
penny. Also a Troy weight.
dram
A dram was originally a Greek drachma, but was
redefined as 1/16 Avoirdupois ounce or 1/8
Apothecaries ounce.
ounce
The ounce was originally 1/12 of a roman pound,
but was redefined as 1/16 for commerce in
Avoirdupois. Probably easier to divide by
dividing in halves, fourths and eighths.
poundal
A poundal is the force necessary to accelerate 1
pound mass 1 foot per second
2.
stone
A stone is a unit still commonly used in Britain
to express a persons weight. Note that a long ton
is an exact multiple. The long ton is still often
used because it is close to a metric ton or 1000
kilograms.
slug
A slug is the mass that is accelerated by 1 foot
per second 2 by
1 pound force.
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
answer.
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