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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.

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.

G-2 Revised November, 2011

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

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.

G-4 Revised November, 2011

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.

G-4 Revised November, 2011

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.

Revised November, 2011 G-5

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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c. English to Metric Conversions

G-6 Revised November, 2011