**acre** (ac or A)

a unit of area used for measuring real estate in English-speaking
countries. "Acre," an Old English word meaning a field, is derived
from the Latin ager and Greek agros, also meaning a field. The acre
was originally defined as the area that could be plowed in a day by
a yoke of oxen. It was in use in England at least as early as the
eighth century, and by the end of the ninth century it was generally
understood to be the area of a field one furlong (40 rods or 10
chains) long by 4 rods (or 1 chain) wide. Thus an acre is 10 square
chains, 160 square rods, 43 560 square feet or 4840 square yards.
There are exactly 640 acres in a square mile. In metric countries
the unit corresponding to the acre is the hectare, which is 10,000
square meters (the area of a square 100 meters on each side). One
acre is equal to 0.404 687 3 hectare

**chain** (ch)

a unit of distance formerly used by surveyors. The traditional
British surveyor's chain, also called Gunter's chain because it was
introduced by the English mathematician Edmund Gunter (1581-1626) in
1620, is 4 rods long: that's equal to exactly 1/80 mile, 1/10
furlong, 22 yards, or 66 feet (20.1168 meters). The traditional
length of a cricket pitch is 1 chain. Gunter's chain has the useful
property that an acre is exactly 10 square chains. The chain was
divided into 100 links.

**foot** (ft or ')

a traditional unit of distance. Almost every culture has used the
human foot as a unit of measurement. The natural foot (pes naturalis
in Latin), an ancient unit based on the length of actual feet, is
about 25 centimeters (9.8 inches). This unit was replaced in early
civilizations of the Middle East by a longer foot, roughly 30
centimeters or the size of the modern unit, because this longer
length was conveniently expressed in terms of other natural units:

1 foot = 3 hands = 4 palms = 12 inches (thumb widths) = 16 digits
(finger widths)

This unit was used in both Greece and Rome; the Greek foot is
estimated at 30.8 centimeters (12.1 inches) and the Roman foot at
29.6 centimeters (11.7 inches). In northern Europe, however, there
was a competing unit known in Latin as the pes manualis or manual
foot. This unit was equal to 2 shaftments, and it was measured "by
hand," grasping a rod with both hands, thumbs extended and touching.
The manual foot is estimated at 33.3 centimeters (13.1 inches).

In England, the Roman foot was replaced after the fall of Rome by
the natural foot and the Saxon shaftment (16.5 centimeters). The
modern foot (1/3 yard or about 30.5 centimeters) did not appear
until after the Norman conquest of 1066. It may be an innovation of
Henry I, who reigned from 1100 to 1135. Later in the 1100s a foot of
modern length, the "foot of St. Paul's," was inscribed on the base
of a column of St. Paul's Church in London, so that everyone could
see the length of this new foot. From 1300, at least, to the present
day there appears be little or no change in the length of the foot.

Late in the nineteenth century, after both Britain and the U.S.
signed the Treaty of the Meter, the foot was officially defined in
terms of the new metric standards. In the U.S., the Metric Act of
1866 defined the foot to equal exactly 1200/3937 meter, or about
30.480 060 96 centimeters. This unit, still used for geodetic
surveying in the United States, is now called the survey foot. In
1959, the U.S. National Bureau of Standards redefined the foot to
equal exactly 30.48 centimeters (about 0.999 998 survey foot). This
definition was also adopted in Britain by the Weights and Measures
Act of 1963, so the foot of 30.48 centimeters is now called the
international foot.

**furlong** (fur)

a traditional unit of distance. Long before the Norman Conquest in
1066, Saxon farmers in England were measuring distance in rods and
furlongs and areas in acres. The word "furlong", from the Old
English fuhrlang, means "the length of a furrow"; it represents the
distance a team of oxen could plow without needing a rest. A furlong
equals 40 rods, which is exactly 10 chains, 220 yards, 660 feet, or
1/8 mile. One furlong is exactly 201.168 meters, so a 200-meter dash
covers a distance very close to a furlong. The length of horse races
is often stated in furlongs.

**hide**

a very old English unit of land area, dating from perhaps the
seventh century. The hide was the amount of land that could be
cultivated by a single plowman and thus the amount of land necessary
to support a family. Depending on local conditions, this could be as
little as 60 acres or as much as 180 acres (24-72 hectares). The
hide was more or less standardized as 120 acres (48.6 hectares)
after the Norman conquest of 1066. The hide continued in use
throughout medieval times, but it is now obsolete. The unit was also
known as the carucate

**perch [1]**

an alternate name for the rod (16.5 feet or 5.0292 meters),
introduced in the twelfth century by the Norman conquerors of
England. The word perch (perche in French: see below) comes from the
Latin pertica (pole). The Romans also had a distance unit called the
pertica, but it was shorter: 10 Roman feet (9.71 English feet or
2.96 meters).

**perch [2]**

a unit of area equal to one square perch [1]. A perch of area covers
exactly 272.25 square feet or about 25.292 85 square meters. There
are 40 perches in a rood and 160 perches in an acre.

**rod (rd)**

a traditional unit of distance equal to 5.5 yards (16 feet 6 inches
or exactly 5.0292 meters). The rod and the furlong were the basic
distance units used by the Anglo-Saxon residents of England before
the Norman conquest of 1066. The Saxons generally called this unit
the gyrd, a word which comes down to us as the name of a different
unit, the yard. "Rod" is another Saxon word which meant just what it
means today: a straight stick. The Normans preferred to call the
gyrd a pole or a perch (a word of French origin, meaning a pole; see
perche). The length of the rod was well established at least as
early as the eighth century. It may have originated as the length of
an ox-goad, a pole used to control a team of 8 oxen (4 yokes).
Scholars are not sure how the rod was related to shorter units. It
may have been considered equal to 20 "natural" feet (actual foot
lengths; see foot), or it may have been measured "by hand" as 30
shaftments. In any case, when the modern foot became established in
the twelfth century, the royal government did not want to change the
length of the rod, since that length was the basis of land
measurement, land records, and taxes. Therefore the rod was
redefined to equal 16.5 of the new feet. This length was called the
"king's perch" at least as early as the time of King Richard the
Lionheart (1198). Although rods and perches of other lengths were
used locally in Britain, the king's perch eventually prevailed. The
relationship between the rod and the other English distance units
was confirmed again by the Parliamentary statute of 1592, which
defined the statute mile to be either 320 rods or 1760 yards, thus
forcing the rod to equal exactly 5.5 yards or 16.5 feet.

**rood** [1]

an old unit of distance, used in several ways. Rood (or roede) is an
old Dutch word meaning a rod or pole. So the rood is in some cases
another name for a rod. But in old England and Scotland the rood was
often longer than a "modern" rod of 16.5 feet; sometimes it was 20
feet, 21 feet, or even 24 feet. In Afrikaans-speaking South Africa,
the rood was a standardized measure equal to 12 Cape feet, which is
12.396 English feet or 3.7783 meters.

**rood** [2]

a traditional unit of area used to measure land. A rood is the area
of a narrow strip of land one furlong (40 rods, or 660 feet) long
and one rod (16.5 feet) wide. Thus the rood is equal to 40 square
rods (or perches), which equals 1210 square yards, or 10 890 square
feet, or exactly 1/4 acre. That would be the area of a lot 22 yards
wide and 55 yards deep, about the size of many suburban lots. One
rood is approximately 1011.714 square meters, or 0.101 171 4
hectare.

**virgate**

an old English unit of land area equal to 1/4 hide. This is roughly
30 acres or 12 hectares. The virgate was also called the yardland or
yard of land

**yard of land, yardland**

one of several traditional units of area in old England; a "yard of
land" (1/4 of a hide) sometimes meant a virgate (roughly 30 acres)
and sometimes a rood (1/4 acre).