Ancient Roman units of measurement

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Bronze modius measure (4th century AD) with inscription acknowledging Imperial regulation of weights and measures Modio de Ponte Punide (M.A.N. 1930-16-1) 01.jpg
Bronze modius measure (4th century AD) with inscription acknowledging Imperial regulation of weights and measures

The units of measurement of ancient Rome were generally consistent and well documented.



The basic unit of Roman linear measurement was the pes (plural: pedes) 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
SourceReported value
in English feet
Foot on the statue of Cossutius0.967 295 mm
Foot on the monument of Statilius0.972 296 mm
Foot of Villalpandus, derived from Congius of Vespasian 0.986 301 mm

William Smith (1851) gives a value of 0.9708 English feet, or about 295.9 mm. [2] An accepted modern value is 296 mm. [3] That foot is also called the pes monetalis to distinguish it from the pes Drusianus (about 333 or 335 mm) sometimes used in some provinces, particularly Germania Inferior. [4] [5]

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

Ancient Roman units of length
Roman unitEnglish
digitus finger 116 pes18.5 mm 0.728 in 
0.0607 ft 
112 pes24.6 mm 0.971 in 
0.0809 ft 
palmus (minor)palm14 pes74 mm 0.243 ft 
palmus maior palm length (lit."greater palm")34 pes222 mm 0.728 ft in late times
pes (plural: pedes)(Roman) foot 1 pes296 mm 0.971 ft sometimes distinguished as the pes monetalis [lower-alpha 1]
palmipesfoot and a palm1+14 pedes370 mm 1.214 ft 
cubitum cubit 1+12 pedes444 mm 1.456 ft 
pes sestertius
step 2+12 pedes0.74 m 2.427 ft 
passus pace 5 pedes1.48 m 4.854 ft 
perch 10 pedes2.96 m 9.708 ft 
actus (length)120 pedes35.5 m 116.496 ft  24 passus or 12 decembeda
stadium stade625 pedes185 m 607.14 ft  600 Greek feet
or 125 passus
or 18 mille [7]
mille passus
mille passuum
(Roman) mile 5,000 pedes1.48 km 4,854 ft 
0.919  mi  
1000 passus or 8 stadia
(Gallic) league 7,500 pedes2.22 km 7,281 ft 
1.379  mi  
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.

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) [8] [9] 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+12 miles). [10] [11]


The ordinary units of measurement of area were:

Ancient Roman units of area
Roman unitEnglish
pes quadratussquare foot1 pes qu.0.0876 m2 0.943 sq ft 
scrupulum or decempeda quadrata100 pedes qu.8.76 m2 94.3 sq ft the square of the standard 10-foot measuring rod
actus simplex480 pedes qu.42.1 m2 453 sq ft 4 × 120 pedes [12]
uncia2,400 pedes qu.210 m2 2,260 sq ft 
clima3,600 pedes qu.315 m2 3,390 sq ft 60 × 60 pedes [12]
actus quadratus or acnua14,400 pedes qu.1,262 m2 13,600 sq ft also called arpennis in Gaul [12]
jugerum 28,800 pedes qu.2,523 m2 27,200 sq ft 
0.623 acres 
heredium2 jugera5,047 m2 54,300 sq ft 
1.248 acres 
centuria 200 jugera50.5 ha  125 acres formerly 100 jugera [12]
saltus800 jugera201.9 ha 499 acres 
modius16 ha 40 acres  Medieval Latin, plural modii [13]
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 or 5,090 sq ft) used in Hispania Baetica and the Gallic candetum or cadetum of 100 feet[ clarification needed ] 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
square feet
of jugerum
dimidium scrupulum5015764.38 m2 47.1 sq ft 
scrupulum10012888.76 m2 94.3 sq ft 
duo scrupula200114417.5 m2 188 sq ft 
sextula40017235.0 m2 377 sq ft 
sicilicus60014852.6 m2 566 sq ft 
semiuncia1,200124105 m2 1,130 sq ft 
uncia2,400112210 m2 2,260 sq ft 
sextans4,80016421 m2 4,530 sq ft 
quadrans7,20014631 m2 6,790 sq ft 
triens9,60013841 m2 9,050 sq ft 
quincunx12,0005121,051 m2 11,310 sq ft 
semis14,400121,262 m2 15,380 sq ft = actus quadratus [2]
septunx16,8007121,472 m2 15,840 sq ft 
bes19,200231,682 m2 18,100 sq ft 
dodrans21,600341,893 m2 20,380 sq ft 
dextans24,000562,103 m2 22,640 sq ft 
deunx26,40011122,313 m2 24,900 sq ft 
jugerum28,80012,523 m2 27,160 sq ft 
Except where noted, based on Millar (1745). [12] Metric equivalents are approximate, converted at 1 pes = 296 mm.


Both liquid and dry volume measurements were based on the sextarius. The sextarius was defined as 148 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) [14] and 580 ml (20 US fl oz). [15]

The core volume units are:

Liquid measure

Ancient Roman liquid measures
Roman unitEqual toMetricImperialUS fluid
ligula1288 congius11.4 mL0.401 fl oz0.385 fl oz
cyathus172 congius45 mL1.58 fl oz1.52 fl oz
acetabulum148 congius68 mL2.39 fl oz2.30 fl oz
quartarius124 congius136 mL4.79 fl oz4.61 fl oz
hemina or cotyla112 congius273 mL9.61 fl oz9.23 fl oz
sextarius16 congius546 mL19.22 fl oz
0.961 pt
18.47 fl oz
1.153 pt
congius1 congius3.27 L5.75 pt
0.719 gal
3.46 qt
0.864 gal
urna4 congii13.1 L2.88 gal3.46 gal
amphora quadrantal8 congii26.2 L5.76 gal6.92 gal
culeus160 congii524 L115.3 gal138.4 gal
Except where noted, based on Smith (1851). [2]
Modern equivalents are approximate.

Dry measure

Ancient Roman dry measures
Roman unitEqual toMetricImperialUS dry
ligula1288 congius11.4 ml0.401 fl oz0.0207 pt
cyathus172 congius45 ml1.58 fl oz0.082 pt
acetabulum148 congius68 ml2.39 fl oz0.124 pt
quartarius124 congius136 ml4.79 fl oz0.247 pt
hemina or cotyla112 congius273 ml9.61 fl oz0.496 pt
sextarius16 congius546 ml19.22 fl oz
0.961 pt
0.991 pt
semimodius1+13 congii4.36 L0.96 gal0.99 gal
modius2+23 congii8.73 L1.92 gal1.98 gal
modius castrensis4 congii12.93 L [16] 2.84 gal2.94 gal
Except where noted, based on Smith (1851). [2]
Modern equivalents are approximate.


A Roman steelyard weight of one dodrans, i.e.
3/4 libra Roman steelyard weight (probably) (FindID 227547).jpg
A Roman steelyard weight of one dodrans, i.e. 34 libra

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. [3] [15] [17] 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 131 BC Lex Papiria. [18] [19]

The divisions of the libra were:

Uncial divisions of the libra
Roman unitEnglish
unciaRoman ounce112 libra27.4 g 0.967 oz lit. "a twelfth" [20]
sescuncia or sescunx18 libra41.1 g 1.45 oz lit. "one and one-half twelfths"
sextans16 libra54.8 g 1.93 oz lit. "a sixth"
14 libra82.2 g 2.90 oz lit. "a fourth"
lit. "triple twelfth"
triens13 libra109.6 g 3.87 oz lit. "a third"
quincunx512 libra137.0 g 4.83 oz lit. "five-twelfths" [21]
semis or semissis12 libra164.5 g 5.80 oz lit. "a half"
septunx712 libra191.9 g 6.77 oz lit. "seven-twelfths"
bes or bessis23 libra219.3 g 7.74 oz lit. "two [parts] of an as"
dodrans34 libra246.7 g 8.70 oz lit. "less a fourth"
dextans56 libra274.1 g 9.67 oz lit. "less a sixth"
deunx1112 libra301.5 g 10.64 oz lit. "less a twelfth"
libraRoman pound
libra [22]
328.9 g 11.60 oz 
0.725 lb 
lit. "balance" [22]
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 unitEnglish
siliqua carat 1144 uncia0.19 g 2.9  gr  
0.0067 oz 
lit. "carob seed"
The Greek κεράτιον (kerátion)
obolus obolus [23] 148 uncia0.57 g 8.8 gr 
0.020 oz 
lit. "obol", from the Greek word for "metal spit" [23]
scrupulum scruple [24] 124 uncia1.14 g 17.6 gr 
0.040 oz 
lit. "small pebble" [24]
semisextula or dimidia sextula112 uncia2.28 g 35.2 gr 
0.080 oz 
lit. "half-sixth", "little sixth"
sextulasextula [25] 16 uncia4.57 g 70.5 gr 
0.161 oz 
lit. "little sixth" [25]
sicilicus or siciliquus14 uncia6.85 g 106 gr 
0.242 oz 
lit. "little sickle"
duella13 uncia9.14 g 141 gr 
0.322 oz 
lit. "little double [sixths]"
semuncia [26]
12 uncia13.7 g 211 gr 
0.483 oz 
lit. "half-twelfth" [26]
unciaRoman ounce27.4 g 423 gr 
0.967 oz 
Derived from unus, "one," in the sense of "single unit of weight." [27]
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. [28] 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 the nundinae , with every eighth day being a market day.

Independent of the nundinae, astrologers kept a seven-day cycle called a hebdomas 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 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.


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, Classical astrologers had a minuta equal to 160 of a day (24 modern minutes), a secunda equal to 13600 of a day (24 modern seconds), and a tertia equal to 1216,000 of a day (0.4 modern seconds).


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)
U+1019x 𐆐 𐆑 𐆒 𐆓 𐆔 𐆕 𐆖 𐆗 𐆘 𐆙 𐆚 𐆛 𐆜
U+101Ax 𐆠
1. ^ As of Unicode version 15.1
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:

See also


  1. The pes Drusianus, 333 or 335 mm, was sometimes used in Roman provinces, particularly Germania Inferior. [4] [5]

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  7. Equivalent to the English cable (600 feet) or furlong (18 mile)
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  26. 1 2 "semuncia, n.", Oxford English Dictionary, 1st ed., Oxford: Oxford University Press, 1911.
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