 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.
Contents
Length
Roman unit Latin name Feet Equivalence one digit digitus ^{1}⁄_{16} 18.5 mm one inch uncia ^{1}⁄_{12} 24.6 mm one palm palmus ^{1}⁄_{4} 74 mm one foot pes 1 29.6 cm^{[1]} one cubit cubitus 1^{ 1}⁄_{2} 44.4 cm one step gradus 2^{ 1}⁄_{2} 0.74 m one pace passus 5 1.48 m one fathom ulna 6 1.78 m one perch pertica 10 2.96 m one arpent actus 120 35.5 m one furlong stadium 625 185 m one mile mille passuum (milliarium) 5000 1.48 km one league leuga 7500 2.2225 km Notes
 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.^{[citation needed]}  A Roman foot was approximately equal to the height of a modern A4 sheet of paper.
Area
Roman unit Latin name Acres Equivalence one square foot pes quadratus ^{1}⁄_{14 400} ~ 876 cm² one square perch scripulum ^{1}⁄_{144} ~ 8.76 m² one aune of furrows actus minimus ^{1}⁄_{30} ~ 42 m² one rood clima ^{1}⁄_{4} ~ 315 m² one acre actus quadratus
also known as acnua1 ~ 1260 m² one yoke iugerum 2 ~ 2520 m² one morn heredium 4 ~ 5040 m² one centurie centuria 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 crosssectional 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 ^{1}⁄_{48} ~ 11.25 ml one dose cyathus ^{1}⁄_{12} ~ 45 ml one sixthsester sextans ^{1}⁄_{6} ~ 90 ml one thirdsester triens ^{1}⁄_{3} ~ 180 ml one halfsester hemina ^{1}⁄_{2} ~ 270 ml one double thirdsester choenix ^{2}⁄_{3} ~ 360 ml one sester sextarius 1 ~ 540 ml one congius congius 6 ~ 3.25 l one urn urna 24 ~ 13 l one jar amphora 48 ~ 26 l one hose culleus 960 ~ 520 l The Roman jar, socalled "amphora quadrantal" is the cubic foot. The congius is halfafoot cubed. The Roman sester is the sixth of a congius.
Dry measures
Roman unit Latin name Pecks Equivalence one drawingspoon acetabulum ^{1}⁄_{128} ~ 67.5 ml one quartersester quartarius ^{1}⁄_{64} ~ 135 ml one halfsester hemina ^{1}⁄_{32} ~ 270 ml one sester sextarius ^{1}⁄_{16} ~ 540 ml one gallon semodius ^{1}⁄_{2} ~ 4^{ 1}⁄_{3} l one peck modius 1 ~ 8^{ 2}⁄_{3} 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. Onethird of a quandrantal is a Roman peck.
Mass
The units of weight (mass) were mostly based on factors of 12. Several of the unit names were also the names of coins during the Roman Republic and had the same fractional value of a larger base unit: libra for mass and as for coin. The modern mass of the libra is estimated to range from 322 to 327 grams (11.4 to 11.5 oz).^{[2]}
Unit of mass Conversion Centum podium 100 libra Mina 20 uncia Libra (podium) 12 uncia Deunx 11 uncia Dextans 10 uncia Dodrans 9 uncia Bes 8 uncia Septunx 7 uncia Semis 6 uncia Quincunx 5 uncia Triens 4 uncia Quadrans 3 uncia Sextans 2 uncia Uncia (ounce) Semuncia ^{1}⁄_{2} uncia Duella ^{1}⁄_{3} uncia Sicilium ^{1}⁄_{4} uncia Miliaresium ^{1}⁄_{5} uncia Solidus (sextula) ^{1}⁄_{6} uncia Denarius ^{1}⁄_{7} uncia Denier ^{1}⁄_{8} uncia Scripulum ^{1}⁄_{3} denier Reference: Cardarelli, François (2003). Encyclopaedia of Scientific Units, Weights and Measures: Their SI Equivalences and Origins. Trans. M.J. Shields. London: SpringerVerlag. pp. 74–5. ISBN 978185233682X. http://books.google.com/books?id=GV1aV7V7I00C&pg=SA3PA72. Retrieved 18 November 2011.
One and a half ounces was called by Romans "sescuncia". 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.^{[citation needed]}
Time
Years
The complicated Roman calendar was replaced by the Julian calendar in 45 BC. In the Julian calendar, an ordinary year is 365 days long, a leap year is 366 days long. Between 45 BC and 1 AD, leap years occurred at irregular intervals. Starting in the year 4 AD, leap years occurred regularly every four years. Year numbers were rarely used; rather, the year was specified by naming the Roman consuls for that year. When a year number was required, the Greek Olympiads were used, or the count of years since the founding of Rome, "Ab urbe condita" in 753 BC. In the middle ages, the year numbering was changed to the Anno Domini count.
Our currently used Gregorian calendar differs from the Julian calendar in that it skips three leap years every four centuries to more closely approximate the length of the tropical year.
Weeks
The Romans grouped days into an eightday cycle called a nundina, with every eighth day being a market day.
Independent of the nundinae, astrologers kept a sevenday cycle called a hebdomada where each day corresponded to one of the seven classical planets, with the first day of the week being Saturnday, followed by Sunday, Moonday, Marsday, Mercuryday, Joveday, and lastly Venusday. Each astrological day was reckoned to begin at sunrise. The Jews also used a sevenday week, which began Saturday evening. The seventh day of the week they called the Sabbath; the other days they numbered rather than named, except for Friday, which could be called either the Parasceve or the sixth day. Each Jewish day was reckoned to begin at sunset. Christians followed the Jewish sevenday week, except that they commonly called the first day of the week the Dominica, or the Lord's day. In 321 Constantine the Great gave his subjects every Sunday off in honor of his family's tutelary deity, the Unconquered Sun, thus cementing the sevenday week into Roman civil society.
Hours
The Romans divided the daytime into twelve horae or hours starting in the morning and ending in the evening. The night was divided into four watches. The duration of these hours varied with seasons; in the winter, when the daylight period was shorter, its 12 hours were correspondingly shorter and its four watches were correspondingly longer.
Astrologers divided the solar day into 24 equal hours, and these astrological hours became the basis for medieval clocks and our modern 24 hour mean solar day.
Although the division of hours into minutes and seconds did not occur until the middle ages, ancient astrologers had a minuta equal to a 60th of a day, and a secunda equal to one 3600th of a day.
See also
References
 ^ Hosch, William L. (ed.) (2010) The Britannica Guide to Numbers and Measurement New York, NY: Britannica Educational Publications, 1st edition. ISBN 9781615301089, p.206
 ^ Laniado, Avshalom; Dashti, Batya (1993). "A Byzantine lead weight from the port of Iamnia (YavnehYam) and the title 'ΈΦΟΡΟΣ". Revue des études byzantines (Paris) 51 (51): 229–35. ISSN 07665598. http://www.persee.fr/web/revues/home/prescript/article/rebyz_07665598_1993_num_51_1_1879. Retrieved 19 November 2011.
External links
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Other systems Categories: Ancient Roman units of measure
 From late Antiquity the Roman foot was sometimes divided into unciae comprising 12 equal parts.
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