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Common
Conversion Errors |
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This page considers the most common conversion errors, when doing conversions
between the 3 measurement systems (Metric, Imperial, and USA). For more general
information on the metric, USA and Imperial systems of measurement, click on
Metric System Conversion Table / Chart and Converter for
Metric Conversions.
The most common errors made when converting to or from the metric
system include:
- Confusion between a fluid ounce and an ounce of weight.
- Confusion between Imperial measures and USA measures.
- Confusion between different units with the same name.
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Converting
Between Imperial and USA Measures |
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There are a number of differences between the Imperial and USA systems of
measurement. Some of these differences have been eliminated by evolving
standards. In particular, in 1959 the Imperial and USA measurements of the inch
(and all its multiples: foot, yard, mile, square foot, square yard, etc.) and
the pound were standardized to the same values. The most common differences that
are still encountered are:
- Measurements of liquid volume. All the common measures of volume
have the same name in both the USA and Imperial systems, but most of them
have different sizes. See
Metric & Imperial Units
for details.
- Measurements of weight. The Imperial pound and the USA pound have
now been standardized to the same weight. However, the Imperial system also
uses the "stone" (which is not used in the USA system) and the
definitions of hundredweight and ton are different in the two systems. See
Metric & Imperial Units
for details.
- Measuring spoons. There are various differences for measuring
spoons (teaspoon, tablespoon, dessertspoon, etc.), see
Cooking Converter for details.
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Measures
With Multiple Definitions |
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In both the Imperial and the USA systems, a number of measures have multiple
definitions. Fortunately, most of these ambiguous measures are not in common
usage. Following is a summary, although we make no claims to it being complete:
- Acre. A "US survey" acre (43, 560 square feet) is larger than a
"commercial acre" (36,000 square feet).
- Barrel. There are seven different barrel sizes used in the USA,
with the size being dependent on the contents. Their names and metric
equivalents are as follows: US cranberry (95.5 liters), US dry (115.628
liters), US liquid (119.24 liters), US federal (117.348 liters), US federal
proof spirits (151.416 liters), US drum (208.4 liters), US petroleum (135
kg.), US petroleum statistical (158.99 liters).
- Bushel. There are many definitions of the bushel. Examples of
USA bushels and their approximate metric equivalents are: Oats bushel (14.5
kg), Barley bushel (21.8 kg), Shelled corn or rye bushel (25.4 kg),
Wheat/soybeans/potatoes bushel (27.2 kg), US volume bushel (35.239 liters).
The Imperial volume bushel is equal to 36.36872 litres.
- Clothing and sizes. Shoe sizes are measured different for
"men", "women" and "children". Likewise, clothing sizes. This is further
complicated by different measurements from one country to another and
different interpretations from one manufacturer to another. See
Clothing and shoe sizes.
- Degree. In addition to degree Fahrenheit (for temperature), there
are at least 12 other definitions of "degree". Ten of these define density,
one defines angle (degree arc) and one defines temperature (degree Rankine).
- Foot. The foot in common use has been standardised (in 1959) to
30.48cm. There is also the "US survey" foot which is slightly larger at
30.480061cm.
- Mile. In addition to the "international" mile which is common
usage (defined as 1.609344 Km.), there are also the "nautical" mile (1.852
Km.) and the "US survey mile" (approximately 1.609347 Km.).
- Ounce. An ounce can either be a measure of volume (in which case
it is referred to as a "fluid ounce") or a measure of weight (in which case
it is referred to as a "ounce weight"). If the term "ounce" is used without
specifying fluid or weight, it is generally assumed to be "ounce weight". The USA
fluid ounce (equal to 29.573 529 562 5 milliliters) is slightly larger than
the Imperial fluid ounce
(equal to 28.413 062 5 milliliters). In addition, there are multiple types
of "ounce (weight)". The ounce (weight) in common usage is the "ounce
avoirdupois" (29.349523125 grams). The "troy ounce" (31.1034768 grams) is
used in various specialist applications, in particular the weights of
precious metals. Consequently, an ounce (weight) of gold is not the same
weight as an ounce (weight) of steel.
- Pint. A pint can be either a "liquid pint" or a "dry pint",
although in common usage one assumes the liquid pint. The USA liquid pint
(approximately 473.2 milliliters) is smaller than the UK liquid pint
(568.261485 milliliters), and
smaller than the USA dry pint (approximately 550.6 milliliters).
- Quart. A quart can be either a "liquid quart" or a "dry quart".
The USA liquid quart is smaller than the UK quart. See above discussion of
Pint.
- Year. There are six different definitions of the "year", although
the differences are not large (except for the "leap year" and the "lunar
year".
- Other. There are two versions of the BTU (British Thermal Unit)
and the calorie; both of these are measures of energy. There are two
versions of the Cable (a measure of length), footcandle, keg (US large beer
and US small beer), minute (solar minute of 60 seconds, sidereal minute of
59.83617 seconds), pace (geometrical and
military), pica. There are several definitions of "point". The term "pound"
is normally used to describe weight, but is also used to describe the
density of paper.
If you would like to suggest any other errors for inclusion in this area,
please Contact us.
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Metric
Conversion |
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To perform metric conversion,
please click on Quick Metric Converter. For
detailed information, click on
Metric System Conversion, which provides metric system
converters and conversion tables. For other related information see the links at
the top of the page.
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