Ancient Roman units of measurement

The ancient Roman units of measurement were primarily founded on the Hellenic system, which in turn were influenced by the Egyptian system and the Mesopotamian system. The Roman units were comparatively consistent and well documented.

Bronze modius measure (4th century AD) with inscription acknowledging Imperial regulation of weights and measures

Length

The basic unit of Roman linear measurement was the pes or Roman foot (plural: pedes). Investigation of its relation to the English 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[1] (30.4919 cm):[2]

Values of the ancient Roman foot determined by Greaves in 1639
Source Reported value in English feet Metric equivalent
Foot on the statue of Cossutius 0.96700  29.486 cm 
Foot on the monument of Statilius 0.97200  29.638 cm 
Foot of Villalpandus, derived from Congius of Vespasian 0.98600  30.065 cm 

Smith (1851) gives a value of 0.9708 English feet, or about 295.9 mm.[3] An accepted modern value is 296 mm.[4]

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.[5] The principal Roman units of length were:

Ancient Roman units of length
Roman unit English name Equal to Metric equivalent Imperial equivalent Notes
digitus finger ​1⁄16 pes 18.5 mm  0.728 in 
0.0607 ft 
uncia
pollex		 inch
thumb		 ​1⁄12 pes 24.6 mm  0.971 in 
0.0809 ft 
palmus palm ​1⁄4 pes 74 mm  0.243 ft 
palmus maior palm length (lit."greater palm") ​3⁄4 pes 222 mm  0.728 ft  in late times
pes (plural: pedes) (Roman) foot 1 pes 296 mm  0.971 ft 
palmipes foot and a palm ​1 1⁄4 pedes 370 mm  1.214 ft 
cubitum cubit ​1 1⁄2 pedes 444 mm  1.456 ft 
gradus
pes sestertius		 step ​2 1⁄2 pedes 0.74 m  2.427 ft 
passus pace 5 pedes 1.48 m  4.854 ft 
decempeda
pertica		 perch 10 pedes 2.96 m  9.708 ft 
actus (length) 120 pedes 35.5 m  116.496 ft  24 passus or 12 decembeda
stadium stade 625 pedes 185 m  607.14 ft  600 Greek feet
or 125 passus
or ​1⁄8 mille[6]
mille passus
mille passuum		 (Roman) mile 5000 pedes 1.48 km  4854 ft 
0.919 mi 		 1000 passus or 8 stadia
leuga
leuca		 (Gallic) league 7500 pedes 2.22 km  7281 ft 
1.379 mi 
Except where noted, based on Smith (1851).[3] 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)[7][8] and in the name of the Nubian land of Triacontaschoenus between the First and Second Cataracts on the Nile (where it had a value closer to 10.5 km or 6 1⁄2 miles).[9][10]

Area

The ordinary units of measurement of area were:

Ancient Roman units of area
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[11]
uncia 2400 pedes qu. 210 m2  2260 sq ft 
clima 3600 pedes qu. 315 m2  3390 sq ft  60 × 60 pedes[11]
actus quadratus or acnua 14400 pedes qu. 1262 m2  13600 sq ft  also called arpennis in Gaul[11]
jugerum 28800 pedes qu. 2523 m2  27200 sq ft 
0.623 acres 
heredium 2 jugera 5047 m2  54300 sq ft 
1.248 acres 
centuria 200 jugera 50.5 ha  125 acres  formerly 100 jugera[11]
saltus 800 jugera 201.9 ha  499 acres 
Except where noted, based on Smith (1851).[3] 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:

Uncial divisions of the jugerum
Roman unit Roman square feet Fraction of jugerum Metric equivalent Imperial equivalent Description
dimidium scrupulum 50 ​1⁄576 4.38 m2  47.1 sq ft 
scrupulum 100 ​1⁄288 8.76 m2  94.3 sq ft 
duo scrupula 200 ​1⁄144 17.5 m2  188 sq ft 
sextula 400 ​1⁄72 35.0 m2  377 sq ft 
sicilicus 600 ​1⁄48 52.6 m2  566 sq ft 
semiuncia 1200 ​1⁄24 105 m2  1130 sq ft 
uncia 2400 ​1⁄12 210 m2  2260 sq ft 
sextans 4800 ​1⁄6 421 m2  4530 sq ft 
quadrans 7200 ​1⁄4 631 m2  6790 sq ft 
triens 9600 ​1⁄3 841 m2  9050 sq ft 
quincunx 12000 ​5⁄12 1051 m2  11310 sq ft 
semis 14400 ​1⁄2 1262 m2  15380 sq ft  = actus quadratus[3]
septunx 16800 ​7⁄12 1472 m2  15840 sq ft 
bes 19200 ​2⁄3 1682 m2  18100 sq ft 
dodrans 21600 ​3⁄4 1893 m2  20380 sq ft 
dextans 24000 ​5⁄6 2103 m2  22640 sq ft 
deunx 26400 ​11⁄12 2313 m2  24900 sq ft 
jugerum 28800 1 2523 m2  27160 sq ft 
Except where noted, based on Millar (1745).[11] Metric equivalents are approximate, converted at 1 pes = 296 mm.

Volume

Both liquid and dry volume measurements were based on the sextarius. The sextarius was defined as ​1⁄48 of a cubic foot, known as an amphora quadrantal. Using the value 296 mm (11.7 in) for the Roman foot, an amphora quadrantal can be computed at approximately 25.9 L (6.8 US gal), so a sextarius (by the same method) would theoretically measure 540.3 ml (19.02 imp fl oz; 18.27 US fl oz), which is about 95% of an imperial pint (568.26125 ml).

Archaeologically, however, the evidence is not as precise. No two surviving vessels measure an identical volume, and scholarly opinion on the actual volume ranges between 500 ml (17 US fl oz)[12] and 580 ml (20 US fl oz).[13]

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

Liquid measure
Ancient Roman liquid measures
Roman unit Equal to Metric Imperial US fluid
ligula ​1⁄288 congius 11.4 mL 0.401 fl oz 0.385 fl oz
cyathus ​1⁄72 congius 45 mL 1.58 fl oz 1.52 fl oz
acetabulum ​1⁄48 congius 68 mL 2.39 fl oz 2.30 fl oz
quartarius ​1⁄24 congius 136 mL 4.79 fl oz 4.61 fl oz
hemina or cotyla ​1⁄12 congius 273 mL 9.61 fl oz 9.23 fl oz
sextarius ​1⁄6 congius 546 mL 19.22 fl oz
0.961 pt		 18.47 fl oz
1.153 pt
congius 1 congius 3.27 L 5.75 pt
0.719 gal		 3.46 qt
0.864 gal
urna 4 congii 13.1 L 2.88 gal 3.46 gal
amphora quadrantal 8 congii 26.2 L 5.76 gal 6.92 gal
culeus 160 congii 524 L 115.3 gal 138.4 gal
Except where noted, based on Smith (1851).[3]
Modern equivalents are approximate.

Dry measure
Ancient Roman dry measures
Roman unit Equal to Metric Imperial US dry
ligula ​1⁄288 congius 11.4 ml 0.401 fl oz 0.0207 pt
cyathus ​1⁄72 congius 45 ml 1.58 fl oz 0.082 pt
acetabulum ​1⁄48 congius 68 ml 2.39 fl oz 0.124 pt
quartarius ​1⁄24 congius 136 ml 4.79 fl oz 0.247 pt
hemina or cotyla ​1⁄12 congius 273 ml 9.61 fl oz 0.496 pt
sextarius ​1⁄6 congius 546 ml 19.22 fl oz
0.961 pt		 0.991 pt
semimodius ​1 1⁄3 congii 4.36 l 0.96 gal 0.99 gal
modius ​2 2⁄3 congii 8.73 l 1.92 gal 1.98 gal
modius castrensis 4 congii 12.93 l[14] 2.84 gal 2.94 gal
Except where noted, based on Smith (1851).[3]
Modern equivalents are approximate.

Weight

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.[4][13][15] 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.[16]

The divisions of the libra were:

Uncial divisions of the libra
Roman unit English name Equal to Metric equivalent Imperial equivalent Description
uncia Roman ounce ​1⁄12 libra 27.4 g  0.967 oz  lit. "a twelfth"[17]
sescuncia or sescunx ​1⁄8 libra 41.1 g  1.45 oz  lit. "​1 1⁄2 twelfths"
sextans ​1⁄6 libra 54.8 g  1.93 oz  lit. "a sixth"
quadrans
teruncius		 ​1⁄4 libra 82.2 g  2.90 oz  lit. "a fourth"
lit. "triple twelfth"
triens ​1⁄3 libra 109.6 g  3.87 oz  lit. "a third"
quincunx ​5⁄12 libra 137.0 g  4.83 oz  lit. "five-twelfths"[18]
semis or semissis ​1⁄2 libra 164.5 g  5.80 oz  lit. "a half"
septunx ​7⁄12 libra 191.9 g  6.77 oz  lit. "seven-twelfths"
bes or bessis ​2⁄3 libra 219.3 g  7.74 oz  lit. "two [parts] of an as"
dodrans ​3⁄4 libra 246.7 g  8.70 oz  lit. "less a fourth"
dextans ​5⁄6 libra 274.1 g  9.67 oz  lit. "less a sixth"
deunx ​11⁄12 libra 301.5 g  10.64 oz  lit. "less a twelfth"
libra Roman pound
libra[19]		 328.9 g  11.60 oz 
0.725 lb 		 lit. "balance"[19]
Except where noted, based on Smith (1851).[3] Metric equivalents are approximate, converted at 1 libra = 328.9 g .

The subdivisions of the uncia were:

Subdivisions of the uncia
Roman unit English name Equal to Metric equivalent Imperial equivalent Description
siliqua carat ​1⁄144 uncia 0.19 g  2.9 gr 
0.0067 oz 		 lit. "carob seed"
The Greek κεράτιον (kerátion)
obolus obolus[20] ​1⁄48 uncia 0.57 g  8.8 gr 
0.020 oz 		 lit. "obol", from the Greek word for "metal spit"[20]
scrupulum scruple[21] ​1⁄24 uncia 1.14 g  17.6 gr 
0.040 oz 		 lit. "small pebble"[21]
semisextula
dimidia sextula		 ​1⁄12 uncia 2.28 g  35.2 gr 
0.080 oz 		 lit. "half-sixth", "little sixth"
sextula sextula[22] ​1⁄6 uncia 4.57 g  70.5 gr 
0.161 oz 		 lit. "little sixth"[22]
sicilicus
siciliquus		 ​1⁄4 uncia 6.85 g  106 gr 
0.242 oz 		 lit. "little sickle"
duella ​1⁄3 uncia 9.14 g  141 gr 
0.322 oz 		 lit. "little double [sixths]"
semuncia half-ounce
semuncia[23]		 ​1⁄2 uncia 13.7 g  211 gr 
0.483 oz 		 lit. "half-twelfth"[23]
uncia Roman ounce 27.4 g  423 gr 
0.967 oz 
Except where noted, based on Smith (1851).[3] Metric equivalents are approximate, converted at 1 libra = 328.9 g .

Unicode
Main article: Ancient Symbols (Unicode block)

A number of special symbols for Roman currency were added to the Unicode Standard version 5.1 (April 2008) as the Ancient Symbols block (U+10190–U+101CF, in the Supplementary Multilingual Plane ).

Ancient Symbols[1][2]
Official Unicode Consortium code chart (PDF)
 0123456789ABCDEF
U+1019x 𐆐 𐆑 𐆒 𐆓 𐆔 𐆕 𐆖 𐆗 𐆘 𐆙 𐆚 𐆛 𐆜
U+101Ax 𐆠
U+101Bx
U+101Cx
Notes
1.^ As of Unicode version 13.0
2.^ Grey areas indicate non-assigned code points

As mentioned above, the names for divisions of an as coin (originally one libra of bronze) were also used for divisions of a libra, and the symbols U+10190–U+10195 are likewise also symbols for weights:

  • U+10190 (𐆐): Sextans
  • U+10191 (𐆑): Uncia
  • U+10192 (𐆒): Semuncia
  • U+10193 (𐆓): Sextula
  • U+10194 (𐆔): Semisextula
  • U+10195 (𐆕): Siliqua

Time

Years

The complicated Roman calendar was replaced by the Julian calendar in 45 BC.[24] 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.

Weeks

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 use 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 begins 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.

Hours
Main article: Roman timekeeping

The Romans divided the daytime into twelve horae or hours starting at sunrise and ending at sunset. 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 ​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 ​1⁄216,000 of a day (0.4 modern seconds).

See also

References
  1. 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
  2. Stecchini, Livio C., "The Origin of English Measures", A History of Measures, retrieved 16 January 2017.
  3. 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
  4. 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
  5. Sextus Julius Frontinus (c. 100 AD) De aquis 1:24. English translation.
  6. Equivalent to the English cable (600 feet) or furlong (​1⁄8 mile)
  7. Edwell, Peter (1 December 2007). Between Rome and Persia: The Middle Euphrates, Mesopotamia and Palmyra Under Roman Control. Routledge. p. 228. ISBN 9781134095735.
  8. Bell, Gertrude; Mason, Fergus (2 June 2014). Amurath to Amurath: Includes Biography of Gertrude Bell. BookCaps Study Guides. p. 105. ISBN 9781629172859.
  9. Herodotus (5 March 1998). The Histories. OUP Oxford. p. 592. ISBN 9780191589553.
  10. Fage, J. D. (1 February 1979). The Cambridge History of Africa. Cambridge University Press. p. 258. ISBN 9780521215923.
  11. 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.
  12. W.H. Jones (1954). "Pliny's Natural History (Introduction to Chapter 6)". Archived from the original on 1 January 2017. Retrieved 1 June 2014.
  13. Zupko, Ronald Edward (1977). British weights & measures: a history from antiquity to the seventeenth century. University of Wisconsin Press. p. 7. ISBN 9780299073404. Retrieved 9 December 2011.
  14. 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.
  15. 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.
  16. "as, n.", Oxford English Dictionary (1st ed.), Oxford: Oxford University Press, 1885.
  17. "ounce, n.1", Oxford English Dictionary, 1st ed., Oxford: Oxford University Press, 1911.
  18. "quincunx, n.", Oxford English Dictionary, 3rd ed., Oxford: Oxford University Press, 2007.
  19. "libra, n.", Oxford English Dictionary, 1st ed., Oxford: Oxford University Press, 1902.
  20. "obelus, n.", Oxford English Dictionary, 3rd ed., Oxford: Oxford University Press, 2004.
  21. "scruple, n.1", Oxford English Dictionary, 1st ed., Oxford: Oxford University Press, 1911.
  22. "sextula, n.", Oxford English Dictionary, 3rd ed., Oxford: Oxford University Press, 2008.
  23. "semuncia, n.", Oxford English Dictionary, 1st ed., Oxford: Oxford University Press, 1911.
  24. "The Julian Calendar". timeanddate.com. Retrieved 25 May 2019.
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