# Measurements in English and Metric Units

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Metric Units. The metric system is a system of measurement that succeeded the decimalized system based on the meter that had been introduced in France in the 1790s.
1. Appendix G
Units of Measure
A. Measurement
Magnitudes of measurements are typically given in terms of a specific unit. In surveying, the
most commonly used units define quantities of length (or distance), area, volume, and horizontal
or vertical angles. The two systems used for specifying units of measure are the English and
metric systems. Units in the English system are historical units of measurement used in
medieval England which evolved from the Anglo-Saxon and Roman systems. The metric system
is a decimalized system of measurement developed in France in late 18th century. Since the
metric system is almost universally used, it is often referred to as the International System of
Units and abbreviated SI.
1. Length
a. English Units
The basic units for length or distance measurements in the English system are the inch,
foot, yard, and mile. Other units of length also include the rod, furlong, and chain.
b. Metric Units
The basic unit of length in the SI system is the meter. The meter was originally intended
to be one ten-millionth of the distance from the Equator to the North Pole (at sea level).
The meter has since been redefined as the distance travelled by light in a vacuum in
1/299,792,458 seconds (i.e. the speed of light in a vacuum is 299,792,458 m/sec).
Subdivisions of the meter are the millimeter, centimeter, and the decimeter, while
multiples of meters include the decameter, hectometer, and kilometer.
2. Units of Measurement
c. English to Metric Conversions
There are two different conversions to relate the foot and the meter. In 1893, the United
States officially defined a meter as 39.37 inches. Under this standard, the foot was equal
to 12/39.37 m (approximately 0.3048 m). In 1959, a new standard was adopted that
defined an inch equal to 2.54 cm. Under this standard, the foot was equal to exactly
0.3048 m. The older standard is now referred to as the U.S. survey foot, while the new
standard is referred to as the international foot. All WYDOT surveys use the U.S.
survey foot definition.
2. Area
a. English Units
In the English system, areas are typically given in square feet or square yards. For larger
area measurements, the acre or square mile may be used. Historically, the acre was
originally established as an area one furlong in length and four rods in width. Laying out
ten of these acres side by side is a square furlong (10 acres). Since a mile is eight
furlongs in length, there are exactly 640 acres in a square mile. A survey township is a
square unit of land six miles on a side that conforms to meridians and parallels. Each
township is further divided into 36 one-square mile sections. Because some of the
townships have boundaries designed to correct for the convergence of meridian lines, not
all townships and their sections are exactly square.
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3. Appendix F
b. Metric Units
Areas in the metric system are given is square meters while larger measurements are
given in hectares.
c. English to Metric Conversions
3. Volume
a. English Units
Volumes in the English system are typically given in cubic feet or cubic yards. For larger
volumes, such as the quantity of water in a reservoir, the acre-foot unit is used. It is
equivalent to the area of an acre having a depth of 1 foot.
b. Metric Units
Volumes in the metric system are given in cubic meters.
c. English to Metric Conversions
4. Mass
The mass of an object is often referred to as its weight though these are different concepts
and quantities. Mass refers to the amount of matter in an object, whereas weight refers to the
Revised November, 2011 G-3
4. Units of Measurement
force experienced by an object due to gravity. In other words, an object with a specific mass
will weigh more on the Earth than the moon.
a. English Units
The avoirdupois pound is the primary unit of mass in the English system. Avoirdupois is
a system of weight based on the 16 ounces per pound rather than the 12 ounces per pound
in the troy system of weight.
b. Metric Units
The kilogram is the unit of mass in the metric system.
c. English to Metric Conversions
The avoirdupois pound is defined as exactly 0.45359237 kg.
5. Angular Measurement
In geometry, any horizontal or vertical angle is measured in degrees. These angles may be
given in decimal degrees or degrees, minutes, and seconds.
The radian is another unit of measure for angles. By definition, a full circle has 2 radians
or 360 degrees.
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5. Appendix F
6. Temperature
a. English Units
The Fahrenheit scale, or degrees Fahrenheit (°F), is used in the United States to measure
temperature. On the Fahrenheit scale, the freezing point of water is 32°F while the
boiling point is 212°F at standard atmospheric pressure. The boiling and freezing points
of water are exactly 180 degrees apart, making each degree Fahrenheit 1/180 of the
interval between the two points.
b. Metric Units
The Celsius scale, or degrees Celsius (°C), is used the metric system to measure
temperature. On the Celsius scale, the freezing point of water is 0°C while the boiling
point is 100°C at standard atmospheric pressure. The boiling and freezing points of water
are exactly 100 degrees apart, making each degree Celsius 1/100 of the interval between
the two points. The Fahrenheit and Celsius scales converge at -40° (i.e. -40°F and -40°C
are the same temperature).
c. English to Metric Conversions
7. Pressure
Atmospheric pressure is the force per unit area exerted against a surface by the weight of the
Earth’s atmosphere above that surface. Because there is less overlying atmospheric mass as
elevation increases, pressure decreases with increasing elevation. The standard atmosphere
(atm) is an international reference for pressure.
a. English Units
In the English system, air pressure is typically measured in inches mercury (inHg).
b. Metric Units
Air pressure is measured in millimeters mercury (mmHg) or millibars (mbars) in the
metric system, but may also be measured in pascals or kilopascals.
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6. Units of Measurement
c. English to Metric Conversions
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