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 congiusofVespasian 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
295 mm
Foot on the monument of Statilius
0.972
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 unit
English
name
Equal
to
Metric
equivalent
Imperial
equivalent
Notes
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 (minor)
palm
1⁄4 pes
74 mm
0.243 ft
palm length (lit."greater palm")
3⁄4 pes
222 mm
0.728 ft
in late times
pes (plural: pedes)
1 pes
296 mm
0.971 ft
sometimes distinguished as the pes monetalis[a]
palmipes
foot and a palm
1+1⁄4 pedes
370 mm
1.214 ft
cubitum
1+1⁄2 pedes
444 mm
1.456 ft
gradus
pes sestertius
2+1⁄2 pedes
0.74 m
2.427 ft
passus
5 pedes
1.48 m
4.854 ft
decempeda
pertica
10 pedes
2.96 m
9.708 ft
actus (length)
120 pedes
35.5 m
116.496 ft
stade
625 pedes
185 m
607.14 ft
600 Greek feet
or 125 passus
or1⁄8 mille[7]
mille passus
mille passuum
5,000 pedes
1.48 km
4,854 ft
0.919 mi
1000 passus or 8 stadia
leuga
leuca
(Gallic) league
7,500 pedes
2.22 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+1⁄2 miles).[10][11]
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[12]
uncia
2,400 pedes qu.
210 m2
2,260 sq ft
clima
3,600 pedes qu.
315 m2
3,390 sq ft
60 × 60 pedes[12]
actus quadratus or acnua
14,400 pedes qu.
1,262 m2
13,600 sq ft
also called arpennisinGaul[12]
28,800 pedes qu.
2,523 m2
27,200 sq ft
0.623 acres
heredium
2 jugera
5,047 m2
54,300 sq ft
1.248 acres
200 jugera
50.5 ha
125 acres
formerly 100 jugera[12]
saltus
800 jugera
201.9 ha
499 acres
modius
16 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 candetumorcadetum 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
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
1,200
1⁄24
105 m2
1,130 sq ft
uncia
2,400
1⁄12
210 m2
2,260 sq ft
sextans
4,800
1⁄6
421 m2
4,530 sq ft
quadrans
7,200
1⁄4
631 m2
6,790 sq ft
triens
9,600
1⁄3
841 m2
9,050 sq ft
quincunx
12,000
5⁄12
1,051 m2
11,310 sq ft
semis
14,400
1⁄2
1,262 m2
15,380 sq ft
= actus quadratus[2]
septunx
16,800
7⁄12
1,472 m2
15,840 sq ft
bes
19,200
2⁄3
1,682 m2
18,100 sq ft
dodrans
21,600
3⁄4
1,893 m2
20,380 sq ft
dextans
24,000
5⁄6
2,103 m2
22,640 sq ft
deunx
26,400
11⁄12
2,313 m2
24,900 sq ft
jugerum
28,800
1
2,523 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 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)[14] and 580 ml (20 US fl oz).[15]
The core volume units are:
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).[2]
Modern equivalents are approximate.
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[16]
2.84 gal
2.94 gal
Except where noted, based on Smith (1851).[2]
Modern equivalents are approximate.
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 BCLex Papiria.[18][19]
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"[20]
sescuncia or sescunx
1⁄8 libra
41.1 g
1.45 oz
lit. "one and one-half 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"[21]
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[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 unit
English
name
Equal
to
Metric
equivalent
Imperial
equivalent
Description
1⁄144 uncia
0.19 g
2.9 gr
0.0067 oz
lit. "carob seed"
The Greek κεράτιον (kerátion)
obolus[23]
1⁄48 uncia
0.57 g
8.8 gr
0.020 oz
lit. "obol", from the Greek word for "metal spit"[23]
scrupulum
1⁄24 uncia
1.14 g
17.6 gr
0.040 oz
lit. "small pebble"[24]
semisextula or dimidia sextula
1⁄12 uncia
2.28 g
35.2 gr
0.080 oz
lit. "half-sixth", "little sixth"
sextula
sextula[25]
1⁄6 uncia
4.57 g
70.5 gr
0.161 oz
lit. "little sixth"[25]
sicilicus or 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[26]
1⁄2 uncia
13.7 g
211 gr
0.483 oz
lit. "half-twelfth"[26]
uncia
Roman ounce
27.4 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 horaeorhours 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 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).
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 ).
0
1
2
3
4
5
6
7
8
9
A
B
C
D
E
F
U+1019x
𐆜
U+101Ax
U+101Bx
U+101Cx
Notes
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:
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