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Ancient Roman weights and measures

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Title: Ancient Roman weights and measures  
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Subject: Siliqua, Roman abacus, Roman commerce, System of measurement, Pace (unit), Lex Licinia Sextia, Comparison of the imperial and US customary measurement systems, Fyrkat, Quinaria, Uncia (unit)
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Ancient Roman weights and measures

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.


The basic unit of Roman linear measurement was the pes or Roman foot. 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]

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 0.967  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.[2] An accepted modern value is 296 mm.[3]

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

Ancient Roman units of length
Roman unit English name Equal to English equivalent Metric equivalent Description
digitus finger 116 pes 0.0607 ft (0.728 in)  18.5 mm 
uncia or pollex inch or thumb 112 pes 0.0809 ft (0.971 in)  24.6 mm 
palmus palm width 14 pes 0.243 ft  74 mm 
palmus major palm length 34 pes 0.728 ft  222 mm  in late times
pes foot 1 pes 0.971 ft  296 mm 
palmipes 114 pedes 1.214 ft  370 mm 
cubitus cubit 112 pedes 1.456 ft  444 mm 
gradus or pes sestertius step 212 pedes 2.427 ft  0.74 m 
passus (double) pace 5 pedes 4.854 ft  1.48 m 
decempeda or pertica perch 10 pedes 9.708 ft  2.96 m 
actus (in length) 120 pedes 116.496 ft  35.5 m 
stadium furlong 625 pedes 607.14 ft  185 m 
mille passuum or milliarium[5][6][7] mile 5000 pedes 4854 ft (0.919 standard mi)  1.48 km 
Gallic leuga league 7500 pedes 7281 ft (1.379 standard mi)  2.22 km 
Except where noted, based on Smith (1851).[2] English and Metric equivalents are approximate, converted at 1 pes = 0.9708 English feet and 296 mm respectively.


The ordinary units of measurement of area were:

Ancient Roman units of area
Roman unit English name Equal to Metric equivalent Description
pes quadratus square foot 1 pes² 0.0876 m² 
scrupulum or decempeda quadrata 100 pedes² 8.76 m²  the square of the standard 10-foot measuring rod
actus simplex 480 pedes² 42.1 m²  4 × 120 pedes[8]
uncia 2400 pedes² 210 m² 
clima 3600 pedes² 315 m²  60 × 60 pedes[8]
actus quadratus or acnua 14400 pedes² 1262 m²  also called arpennis in Gaul[8]
jugerum 28800 pedes² 2523 m² 
heredium 2 jugera 5047 m² 
centuria 200 jugera 50.5 ha  formerly 100 jugera[8]
saltus 800 jugera 201.9 ha 
Except where noted, based on Smith (1851).[2] 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) 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 Description
dimidium scrupulum 50 1576 4.38 m² 
scrupulum 100 1288 8.76 m² 
duo scrupula 200 1144 17.5 m² 
sextula 400 172 35.0 m² 
sicilicus 600 148 52.6 m² 
semiuncia 1200 124 105 m² 
uncia 2400 112 210 m² 
sextans 4800 16 421 m² 
quadrans 7200 14 631 m² 
triens 9600 13 841 m² 
quincunx 12000 512 1051 m² 
semis 14400 12 1262 m²  = actus quadratus[2]
septunx 16800 712 1472 m² 
bes 19200 23 1682 m² 
dodrans 21600 34 1893 m² 
dextans 24000 56 2103 m² 
deunx 26400 1112 2313 m² 
jugerum 28800 1 2523 m² 
Except where noted, based on Millar (1745).[8] Metric equivalents are approximate, converted at 1 pes = 296 mm.


Both liquid and dry measures were based on the sextarius. As no two surviving examples are identical, scholarly opinion ranges from 0.53 l[9] to 0.58 l.[10] Cardarelli gives a value 0.54928 l.[11]

Since the Romans themselves defined the sextarius as 1/48th of an amphora quadrantal, and the amphora quadrantal as one cubic foot, assuming a value of 296 mm for the Roman foot yields a theoretical value for the sextarius of about 540.3 ml, which falls comfortably within the accepted range.

Liquid measures

The Roman jar, so-called "amphora quadrantal" is the cubic foot. The congius is a half-foot cubed.

Ancient Roman liquid measures
Roman unit English name Equal to Metric equivalent Description
ligula 148 sextarius  11.4 ml 
cyathus 112 sextarius  45 ml 
acetabulum 18 sextarius  68 ml 
quartarius 14 sextarius  136 ml 
hemina or cotyla 12 sextarius  273 ml 
sextarius 546 ml  a sixth of a congius
congius 6 sextarii  3.27 l 
urna 4 congii  13.1 l 
amphora quadrantal 8 congii  26.2 l 
culeus 160 congii  524 l 
Except where noted, based on Smith (1851).[2] Metric equivalents are approximate.

Dry measures

Ancient Roman dry measures
Roman unit English name Equal to Metric equivalent Description
ligula 148 sextarius  11.4 ml 
cyathus 112 sextarius  45 ml 
acetabulum 18 sextarius  68 ml 
quartarius 14 sextarius  136 ml 
hemina or cotyla 12 sextarius  273 ml 
sextarius 546 ml  a sixth of a congius
semimodius 8 sextarii  4.36 l 
modius 16 sextarii  8.73 l 
Except where noted, based on Smith (1851).[2] Metric equivalents are approximate.


The units of weight (in the everyday sense of the word; technically, "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 grams (11.4 to 11.6 oz) with 5076 grains or 328.9 grams (11.60 oz) an accepted figure.[3][10][12]

The uncial divisions of the as or libra were:

Uncial divisions of the libra
Roman unit English name Equal to Metric equivalent Description
uncia Roman ounce 112 libra 27.4 g 
sescuncia or sescunx 18 libra 41.1 g 
sextans 16 libra 54.8 g 
quadrans or teruncius 14 libra 82.2 g 
triens 13 libra 109.6 g 
quincunx 512 libra 137.0 g 
semis or semissis 12 libra 164.5 g 
septunx 712 libra 191.9 g 
bes or bessis 23 libra 219.3 g 
dodrans 34 libra 246.7 g 
dextans 56 libra 274.1 g 
deunx 1112 libra 301.5 g 
as or libra Roman pound 328.9 g 
Except where noted, based on Smith (1851).[2] 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 Description
siliqua 1144 uncia 0.19 g 
obolus 148 uncia 0.57 g 
scrupulum 124 uncia 1.14 g 
semisextula 112 uncia 2.28 g 
sextula 16 uncia 4.57 g 
sicilicius 14 uncia 6.85 g 
duella 13 uncia 9.14 g 
semuncia 12 uncia 13.7 g 
uncia Roman ounce 27.4 g 
Except where noted, based on Smith (1851).[2] 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 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.

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, Jove-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.


Main article: Roman timekeeping

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


External links

  • Proposal to Add Ancient Roman Weights and Monetary Signs to UCS (Universal Character Set)

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