Definitions

Ancient Roman

Ancient Roman units of measurement

The ancient Roman units of measurement were built on the Hellenic system with Egyptian, Hebrew, and Mesopotamian influences. The Roman units were comparatively consistent and well documented.

Length

  Modern metrologists have found the Roman foot to be of the Nippur cubit.

Roman unit Latin name Feet Equivalence
one digit digitus 18.5 mm
one inch uncia 24.6 mm
one palm palmus 74 mm
one foot pes 1 296 mm
one cubit cubitus 444 mm
one step gradus 0.74 m
one pace passus 5 1.48 m
one perch pertica 10 2.96 m
one arpent actus 120 35.5 m
one stadium stadium 625 185 m
one mile milliarium 5000 1.48 km
one league leuga 7500 2.22 km

Notes

  1. From late Antiquity the Roman foot was sometimes divided into unciae comprising 12 equal parts.
    The ancient digit measure, however, largely dominated before the beginning of the Middle Ages.
  2. The value of the historical Roman foot scientifically obtained through modern statistical methods is 296.2 mm ± 0.5 mm, or about (296.2 ±0.17%) mm (cf. Rottländer, Tübingen, Germany). The table above is based on this value, but rounded to the millimetre precision for the foot.
  3. The widely accepted ratio between the Roman foot and the English foot is 36:35. That is, 36 Roman feet to 35 English feet, making the Roman foot slightly shorter than its modern equivalent. The latter one is 16/28 Mesopotamian cubit and the ratio between this one and the Roman cubit is 20:24. If the present English foot is taken as for reference, the Roman foot should be 296 1/3 mm or approximately 11.65 English inches. That is within the margin obtained by R.C.A. Rottländer (see references).
  4. A Roman foot can be visualised as being approximately equal to the height of an A4 sheet of paper(297mm). This comparison, although descriptive, is +0.27% out of the range given above.

Area

Roman unit Latin name Acres Equivalence

one square foot
pes quadratus
~ 876 cm²
one square perch
scripulum
~ 8.76 m²
one aune of furrows
actus minimus
~ 42 m²
one rood
clima
~ 315 m²
one acre
actus quadratus
also known as acnua
1
~ 1260 m²
one yoke
iugerum
2
~ 2520 m²
one morn
heredium
4
~ 5040 m²
one centurie
centurium
400
~ 50.5 ha
one "quadruplex"
saltus
1600
~ 201.9 ha
The Roman acre is the squared Roman arpent, 120 pedes by 120 pedes. This equals 14 400 square feet or about 0.126 hectares.

The Romans also had a unit of area called a quinaria, which was used to measure the cross-sectional area of pipes. One quinaria was considered to be roughly 4.2 cm².

Note:  Some researchers assert that the Roman surveyors used a perch of ten Greek "Pous of Kyrenaika", i.e. 3.087 m instead of the perch of ten of their own feet, equal 2.964 m.
According to this hypothesis  – currently not supported by the majority of modern metrologists –; all the Roman area measures should be multiplied by 625/576, i.e. 8.5 % larger.
If the irrefutable proof for the real existence of a Roman surveyor perch of 10 Roman feet  6⅔ digits can be adduced, then the saltus equates to one Roman square mile exactly.

Volume

Liquid measures

Roman unit Latin name Sesters Equivalence

one spoonful
ligula
~ cl
one dose
cyathus
~ cl
one sixth-sester
sextans
~ 9 cl
one third-sester
triens
~ 18 cl
one half-sester
hemina
~ 27 cl
one double third-sester
choenix
~ 36 cl
one sester
sextarius
1
~ 54 cl
one congius
congius
6
~ l
one urn
urna
24
~ 13 l
one jar
amphora
48
~ 26 l
one hose
culleus
960
~ 520 l
The Roman jar, so-called "amphora quadrantal" is the cubic foot. The congius is half-a-foot cubed. The Roman sester is the sixth of a congius.

Dry measures

Roman unit Latin name Pecks Equivalence

one drawing-spoon
acetabulum
~ cl
one quarter-sester
quartarius
~ cl
one half-sester
hemina
~ 27 cl
one sester
sextarius
~ 54 cl
one gallon
semodius
~ l
one peck
modius
1
~ l
one bushel
quadrantal
3
~ 26 l
Like the jar, the Roman bushel or "quadrantal" is one cubic foot. It is almost 26.027 litres. One-third of a quandrantal is a Roman peck.

Mass and coins

Roman unit
Latin name
Drachms
Equivalence
one chalcus
chalcus
1 / 48
~ 71 mg
one siliqua
siliqua
1 / 18
~ 189⅓ mg
one obolus
obolus
1 / 6
~ 0.568 g
one scruple
scrupulum
1 / 3
~ 1.136 g
one dram
drachma
1
~ 3.408 g
one shekel
sicilicus
2
~ 6.816 g
one ounce
uncia
8
~ 27.264 g
one pound
libra
96
~ 327.168 g
one mine
mina
128
~ 436.224 g

The Roman pound is exactly three quarters of the Greek mine.
Thus the Greek and Roman drachm is related by the ratio 32 to 25.

All the multiples of the Roman ounce have their own names
  1 ounce    =
uncia
  7 ounces  =
septunx
  2 ounces  =
semis
  8 ounces  =
bes
  3 ounces  =
triens
  9 ounces  =
dodrans
  4 ounces  =
quadrans
10 ounces  =
dextans
  5 ounces  =
quincunx
11 ounces  =
deunx
  6 ounces  =
sextans
12 ounces  =
as

One and a half ounces was called by Romans "sescuncia". Some of these nouns were used to designate Roman bronze coins.

Time

The Julian calendar was introduced in 45 BC replacing the earlier Roman calendar. In the Julian calendar as in the Gregorian calendar an ordinary year is 365 days long and a leap year is 366 days long. The difference is which years are leap years. In the Julian calendar every fourth year is a leap year. The Gregorian calendar uses a more complex algorithm to more closely approximate the length of the tropical year.

References

See also

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