The ancient Roman units of measurement were primarily founded on the Hellenic system, which in turn was influenced by the Egyptian system and the Mesopotamian system.^{[]} The Roman units were comparatively consistent and well documented.
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 measuringrods found in the ruins of Rome, the pavingstones 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]} (30.4919cm):^{[2]}
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 subdivided 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:
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]}
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 m^{2}  0.943 sq ft  
scrupulum or decempeda quadrata  100 pedes qu.  8.76 m^{2}  94.3 sq ft  the square of the standard 10foot measuring rod  
actus simplex  480 pedes qu.  42.1 m^{2}  453 sq ft  4 × 120 pedes^{[11]}  
uncia  2400 pedes qu.  210 m^{2}  2260 sq ft  
clima  3600 pedes qu.  315 m^{2}  3390 sq ft  60 × 60 pedes^{[11]}  
actus quadratus or acnua  14400 pedes qu.  1262 m^{2}  13600 sq ft  also called arpennis in Gaul^{[11]}  
jugerum  28800 pedes qu.  2523 m^{2}  27200 sq ft 0.623 acres 

heredium  2 jugera  5047 m^{2}  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 m^{2} 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:
Roman unit  Roman square feet  Fraction of jugerum  Metric equivalent  Imperial equivalent  Description 

dimidium scrupulum  50  1⁄576  4.38 m^{2}  47.1 sq ft  
scrupulum  100  1⁄288  8.76 m^{2}  94.3 sq ft  
duo scrupula  200  1⁄144  17.5 m^{2}  188 sq ft  
sextula  400  1⁄72  35.0 m^{2}  377 sq ft  
sicilicus  600  1⁄48  52.6 m^{2}  566 sq ft  
semiuncia  1200  1⁄24  105 m^{2}  1130 sq ft  
uncia  2400  1⁄12  210 m^{2}  2260 sq ft  
sextans  4800  1⁄6  421 m^{2}  4530 sq ft  
quadrans  7200  1⁄4  631 m^{2}  6790 sq ft  
triens  9600  1⁄3  841 m^{2}  9050 sq ft  
quincunx  12000  5⁄12  1051 m^{2}  11310 sq ft  
semis  14400  1⁄2  1262 m^{2}  15380 sq ft  = actus quadratus^{[3]} 
septunx  16800  7⁄12  1472 m^{2}  15840 sq ft  
bes  19200  2⁄3  1682 m^{2}  18100 sq ft  
dodrans  21600  3⁄4  1893 m^{2}  20380 sq ft  
dextans  24000  5⁄6  2103 m^{2}  22640 sq ft  
deunx  26400  11⁄12  2313 m^{2}  24900 sq ft  
jugerum  28800  1  2523 m^{2}  27160 sq ft  
Except where noted, based on Millar (1745).^{[11]} 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)^{[12]} and 580 ml (20 US fl oz).^{[13]}
The core volume units are:
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. 
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. 
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:
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. "fivetwelfths"^{[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. "seventwelfths"  
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:
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 (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. "halfsixth", "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  halfounce semuncia^{[23]} 
1⁄2 uncia  13.7 g  211 gr 0.483 oz 
lit. "halftwelfth"^{[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 . 
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+10190U+101CF, in the Supplementary Multilingual Plane ).
Ancient Symbols^{[1]}^{[2]} Official Unicode Consortium code chart (PDF)  
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+10190U+10195 are likewise also symbols for weights:
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.
The Romans grouped days into an eightday cycle called a nundina, with every eighth day being a market day.
Independent of the nundinae, astrologers kept a sevenday cycle called a hebdomada where each day corresponded to one of the seven classical planets, with the first day of the week being Saturnday, followed by Sunday, Moonday, Marsday, Mercuryday, Jupiterday, and lastly Venusday. Each astrological day was reckoned to begin at sunrise. The Jews also use a sevenday 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 sevenday 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 sevenday 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 24hour 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).