Ancient Roman units of measurement
The ancient Roman units of measurement were largely built on the Hellenic system, which in turn was built upon Egyptian and Mesopotamian influences. The Roman units were comparatively consistent and well documented.
The basic unit of Roman linear measurement was the pes or Roman foot. Investigation of its relation to the English (Imperial) foot goes back at least to 1647, when John Greaves published his Discourse on the Romane foot. Greaves visited Rome in 1639, and measured, among other things, the foot measure on the tomb of Titus Statilius Aper, that on the statue of Cossutius formerly in the gardens of Angelo Colocci, the congius of Vespasian previously measured by Villalpandus, a number of brass measuring-rods found in the ruins of Rome, the paving-stones of the Pantheon and many other ancient Roman buildings, and the distance between the milestones on the Appian Way. He concluded that the Cossutian foot was the "true" Roman foot, and reported these values compared to the iron standard of the English foot in the Guildhall in London:
|Source||Reported value in English feet||Metric equivalent|
|Foot on the statue of Cossutius||0.967||294.7 mm|
|Foot on the monument of Statilius||0.972||296.3 mm|
|Foot of Villalpandus, derived from Congius of Vespasian||0.986||300.5 mm|
|Metric equivalents are approximate.|
Smith (1851) gives a value of 0.9708 English feet, or about 295.9 mm. An accepted modern value is 296 mm.
The Roman foot was sub-divided either like the Greek pous into 16 digiti or fingers; or into 12 unciae or inches. Frontinus writes in the 1st century AD that the digitus was used in Campania and most parts of Italy. The principal Roman units of length were:
|Roman unit||English name||Equal to||Metric equivalent||Imperial equivalent||Notes|
|digitus||finger||1⁄16 pes||18.5 mm||0.728 in
|1⁄12 pes||24.6 mm|| 0.971 in
|palmus||palm||1⁄4 pes||74 mm||0.243 ft|
|palmus major||palm length (lit."greater palm")||3⁄4 pes||222 mm||0.728 ft||in late times|
|pes||(Roman) foot||1 pes||296 mm||0.971 ft|
|palmipes||foot and a palm||1 1⁄4 pedes||370 mm||1.214 ft|
|cubitus||cubit||1 1⁄2 pedes||444 mm||1.456 ft|
|step||2 1⁄2 pedes||0.74 m||2.427 ft|
|passus||pace||5 pedes||1.48 m||4.854 ft|
|perch||10 pedes||2.96 m||9.708 ft|
|actus (length)||120 pedes||35.5 m||116.496 ft||60 passus or 12 decembeda|
|stadium||stade||625 pedes||185 m||607.14 ft|| 600 Greek feet|
or 125 passus
or 1⁄8 mille
| mille passus
|(Roman) mile||5000 pedes||1.48 km||4854 ft
|1000 passus or 8 stadia|
|leuga||(Gallic) league||7500 pedes||2.22 km||7281 ft
|Except where noted, based on Smith (1851). English and Metric equivalents are approximate, converted at 1 pes = 0.9708 English feet and 296 mm respectively.|
Other units include the schoenus (from the Greek for "rush rope") used for the distances in Isidore of Charax's Parthian Stations (where it had a value around 5 km or 3 miles) and in the name of the Nubian land of Triakontaschoenus between the First and Second Cataracts on the Nile (where it had a value closer to 10.5 km or 6 1⁄2 miles).
The ordinary units of measurement of area were:
|Roman unit||English name||Equal to||Metric equivalent||Imperial equivalent||Description|
|pes quadratus||square foot||1 pes qu.||0.0876 m2||0.943 sq ft|
|scrupulum or decempeda quadrata||100 pedes qu.||8.76 m2||94.3 sq ft||the square of the standard 10-foot measuring rod|
|actus simplex||480 pedes qu.||42.1 m2||453 sq ft||4 × 120 pedes|
|uncia||2400 pedes qu.||210 m2||2260 sq ft|
|clima||3600 pedes qu.||315 m2||3390 sq ft||60 × 60 pedes|
|actus quadratus or acnua||14400 pedes qu.||1262 m2||13600 sq ft||also called arpennis in Gaul|
|jugerum||28800 pedes qu.||2523 m2|| 27200 sq ft
|heredium||2 jugera||5047 m2|| 54300 sq ft
|centuria||200 jugera||50.5 ha||125 acres||formerly 100 jugera|
|saltus||800 jugera||201.9 ha||499 acres|
|Except where noted, based on Smith (1851). Metric equivalents are approximate, converted at 1 pes = 296 mm.|
Other units of area described by Columella in his De Re Rustica include the porca of 180 × 30 Roman feet (about 473 m2 or 5,090 sq ft) used in Hispania Baetica and the Gallic candetum or cadetum of 100 feet in the city or 150 in the country. Columella also gives uncial divisions of the jugerum, tabulated by the anonymous translator of the 1745 Millar edition as follows:
Both liquid and dry measures were based on the sextarius. As no two surviving examples are identical, scholarly opinion ranges from 530 ml (18 US fl oz) to 580 ml (20 US fl oz). Cardarelli gives a value 549.28 ml (18.573 US fl oz). A 1952 estimate for its value in Pliny the Elder's Natural History estimated it as 500 ml (17 US fl oz).
Since the Romans themselves defined the sextarius as 1⁄48 of an amphora quadrantal, and the amphora quadrantal as one cubic foot, assuming a value of 296 mm (11.7 in) for the Roman foot yields a theoretical value for the sextarius of about 540.3 ml (18.27 US fl oz), which falls comfortably within the accepted range.
The core volume units are:
- amphora quadrantal (Roman jar) – one cubic pes (Roman foot)
- congius – a half-pes cube (thus 1⁄8 amphora quadrantal)
- sextarius – literally 1⁄6, of a congius
The units of weight or 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 weight and as for coin. Modern estimates of the libra range from 322 to 329 g (11.4 to 11.6 oz) with 5076 grains or 328.9 g (11.60 oz) an accepted figure. The as was reduced from 12 ounces to 2 after the First Punic War, to 1 during the Second Punic War, and to half an ounce by the 191 BC Lex Papiria.
The divisions of the libra were:
The subdivisions of the uncia were:
|Roman unit||English name||Equal to||Metric equivalent||Imperial equivalent||Description|
|siliqua||carat||1⁄144 uncia||0.19 g|| 2.9 gr
| lit. "carob seed"|
The Greek κεράτιον (kerátion)
|obolus||obolus||1⁄48 uncia||0.57 g|| 8.8 gr
|lit. "obol", from the Greek word for "metal spit"|
|scrupulum||scruple||1⁄24 uncia||1.14 g|| 17.6 gr
|lit. "small pebble"|
|semisextula||1⁄12 uncia||2.28 g|| 35.2 gr
|lit. "half-little sixth"|
|sextula||sextula||1⁄6 uncia||4.57 g|| 70.5 gr
|lit. "little sixth"|
|1⁄4 uncia||6.85 g|| 106 gr
|lit. "little sickle"|
|duella||1⁄3 uncia||9.14 g|| 141 gr
|lit. "little double [sixths]"|
|1⁄2 uncia||13.7 g|| 211 gr
|uncia||Roman ounce||27.4 g|| 423 gr
|Except where noted, based on Smith (1851). Metric equivalents are approximate, converted at 1 libra = 328.9 g .|
The complicated Roman calendar was replaced by the Julian calendar in 45 BC. In the Julian calendar, an ordinary year is 365 days long, and a leap year is 366 days long. Between 45 BC and AD 1, leap years occurred at irregular intervals. Starting in AD 4, 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. (As consuls' terms latterly ran from January to December, this eventually caused January, rather than March, to be considered the start of the 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.
The calendar used in most of the modern world, the 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.
The Romans grouped days into an eight-day cycle called a nundina, with every eighth day being a market day.
Independent of the nundinae, astrologers kept a seven-day cycle called a hebdomada where each day corresponded to one of the seven classical planets, with the first day of the week being Saturn-day, followed by Sun-day, Moon-day, Mars-day, Mercury-day, Jupiter-day, and lastly Venus-day. Each astrological day was reckoned to begin at sunrise. The Jews also used a seven-day week, which began Saturday evening. The seventh day of the week they called 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 seven-day 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 seven-day week into Roman civil society.
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.
Although the division of hours into minutes and seconds did not occur until the middle ages, ancient astrologers had a minuta equal to 1⁄60 of a day (24 modern minutes), a secunda equal to 1⁄3600 of a day (24 modern seconds), and a tertia equal to 1⁄216000 of a day (0.4 modern seconds).
Ancient Roman units of measurement were added to the Unicode Standard in April 2008 with the release of version 5.1.
The Unicode block for ancient Roman units of measurement, called Ancient Symbols, is U+10190–U+101CF, i.e. in the upper plane:
| Ancient Symbols|
Official Unicode Consortium code chart (PDF)
- Greaves, John (1647) A discourse of the Romane foot and denarius; from whence, as from two principles, the measures and weights used by the ancients may be deduced London: William Lee
- Smith, Sir William; Charles Anthon (1851) A new classical dictionary of Greek and Roman biography, mythology, and geography partly based upon the Dictionary of Greek and Roman biography and mythology New York: Harper & Bros. Tables, pp. 1024–30
- Hosch, William L. (ed.) (2010) The Britannica Guide to Numbers and Measurement New York, NY: Britannica Educational Publications, 1st edition. ISBN 978-1-61530-108-9, p.206
- Sextus Julius Frontinus (c. 100 AD) De aquis 1:24. English translation.
- Equivalent to the English cable (600 feet) or furlong ( 1⁄8 mile)
- Edwell, Peter (1 December 2007). "Between Rome and Persia: The Middle Euphrates, Mesopotamia and Palmyra Under Roman Control". Routledge. p. 228 – via Google Books.
- Bell, Gertrude; Mason, Fergus (2 June 2014). "Amurath to Amurath: Includes Biography of Gertrude Bell". BookCaps Study Guides. p. 105 – via Google Books.
- Herodotus (5 March 1998). "The Histories". OUP Oxford. p. 592 – via Google Books.
- Fage, J. D. (1 February 1979). "The Cambridge History of Africa". Cambridge University Press. p. 258 – via Google Books.
- Lucius Junius Moderatus Columella, Anon. (trans.) (1745) L. Junius Moderatus Columella of Husbandry, in Twelve Books: and his book, concerning Trees. Translated into English, with illustrations from Pliny, Cato, Varro, Palladius and other ancient and modern authors London: A. Millar. pp xiv, 600. Pages 208–216.
- Encyclopædia Britannica almanac 2008. Encyclopædia Britannica. 2009. p. 162. ISBN 978-1-59339-475-2. Retrieved December 2011. Check date values in:
- Zupko, Ronald Edward (1977). British weights & measures: a history from antiquity to the seventeenth century. University of Wisconsin Press. p. 7. Retrieved 9 December 2011.
- Cardarelli, François; M.J. Shields (tr.) (2003). Encyclopaedia of Scientific Units, Weights and Measures: Their SI Equivalences and Origins. Springer. pp. 74–5. ISBN 9781852336820.
- W.H. Jones (1954). "Pliny's Natural History (Introduction to Chapter 6)".
- Dominic Rathbone, "Earnings and Costs: Living Standards and the Roman Economy (First to Third Centuries AD), p. 301, in Alan Bowman and Andrew Wilson, Quantifying the Roman Economy: Methods and Problems.
- Skinner, Frederick George (1967). Weights and measures: their ancient origins and their development in Great Britain up to A.D. 1855. H.M.S.O. p. 65. Retrieved 9 December 2011.
- "as, n.", Oxford English Dictionary (1st ed.), Oxford: Oxford University Press, 1885.
- "ounce, n.1", Oxford English Dictionary, 1st ed., Oxford: Oxford University Press, 1911.
- "quincunx, n.", Oxford English Dictionary, 3rd ed., Oxford: Oxford University Press, 2007.
- "libra, n.", Oxford English Dictionary, 1st ed., Oxford: Oxford University Press, 1902.
- "obelus, n.", Oxford English Dictionary, 3rd ed., Oxford: Oxford University Press, 2004.
- "scruple, n.1", Oxford English Dictionary, 1st ed., Oxford: Oxford University Press, 1911.
- "sextula, n.", Oxford English Dictionary, 3rd ed., Oxford: Oxford University Press, 2008.
- "semuncia, n.", Oxford English Dictionary, 1st ed., Oxford: Oxford University Press, 1911.