(this information taken from:)
Manual of Instructions for the Survey of the Public Lands of the United States; 1973
Prepared by the Bureau of Land Management, Technical Bulletin 6;  pub. U.S. Dept of Interior

p. 18

Chapter II

Methods of Survey

The methods described in this chapter comprise the specifications for determining the length and direction of lines.

DISTANCE MEASUREMENT

Units

2-1. The law prescribes the chain as the unit of linear measure for the survey of the public lands. All returns of measurements in the rectangular system are made in the true horizontal distance in miles, chains, and links. (Exceptions are special requirements for measurement in feet in townsite surveys, chapter VII, and mineral surveys, chapter X.)

Units of Linear Measure

1 chain

=100 links
 =66 feet

1 mile

=80 chains

 

=5,280 feet
 

Units of Area

1 acre

=10 square chains

 

=43,560 square feet

1 square mile

=640 acres
 
The chain unit, devised in the seventeenth century by Edmund Gunter, an English astronomer, is so designed that 10 square chains are equivalent to one acre. In the English colonial area of the United States the boundaries of land were usually measured in the chain unit, but lengths of lines were frequently expressed in poles. One pole is equal to 25 links, and four poles equal one chain. The field notes of some early rectangular surveys in the southern States show the distance in "perches," equivalent to poles. The term now commonly used for the same distance is the rod.

Land grants by the French crown were made in arpents. The arpent is a unit of area, but the side of a square arpent came to be used for linear description. The Spanish crown and the Mexican Government granted lands which were usually described in linear varas. Both the arpent and the vara have slightly different values in different States. The conversions most often needed are shown in the Standard Field Tables.

(The information below NOT taken from The Manual of Instructions for the Survey of the Public Lands.)
Surveying Measurements
  • 1 yard = 3 ft = 0.9144 meter
  • 1 rod, perch, or pole = 25 links = 16.5 ft
  • 4 rods = 1 chain
  • 1 chain = 4 rods = 66 ft = 100 links
  • 10 chains = 1 furlong
  • 1 link = 1/100 of surveyor's chain = 7.92 inches
  • 25 links = 1 rod = 16.5 ft
  • 100 links = 1 chain = 66 ft
  • 1 furlong = 10 chains = 1/8 mile = 220 yards = 660 ft = 201.168 meters
  • 8 furlongs = 1 mile
  • 1 mile = 80 chains = 320 rods = 1,760 yards = 5,280 ft = 1,609.344 meters
  • league = 3 statute miles = 4,828.032 meters
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