# Ancient Roman units of measurement

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

## Length

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
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. An accepted modern value is 296 mm. 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.
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. 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 (minor) | 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 | sometimes distinguished as the pes monetalis |
| 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 | path, track | 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 |
| mille passus mille passuum | (Roman) mile | 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). 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) 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).

## 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 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 10-foot measuring rod |
| actus simplex | | 480 pedes qu. | 42.1 m$^2$ | 453 sq ft | 4 × 120 pedes |
| uncia | | 2,400 pedes qu. | 210 m$^2$ | 2,260 sq ft | |
| clima | | 3,600 pedes qu. | 315 m$^2$ | 3,390 sq ft | 60 × 60 pedes |
| actus quadratus or acnua | | 14,400 pedes qu. | 1,262 m$^2$ | 13,600 sq ft | also called arpennis in Gaul |
| jugerum | | 28,800 pedes qu. | 2,523 m$^2$ | 27,200 sq ft 0.623 acres | |
| heredium | | 2 jugera | 5,047 m$^2$ | 54,300 sq ft 1.248 acres | |
| centuria | | 200 jugera | 50.5 ha | 125 acres | formerly 100 jugera |
| saltus | | 800 jugera | 201.9 ha | 499 acres | |
| modius | | | 16 ha | 40 acres | Medieval Latin, plural modii |
| Except where noted, based on Smith (1851). 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 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 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 | 1,200 | 1⁄24 | 105 m$^2$ | 1,130 sq ft | |
| uncia | 2,400 | 1⁄12 | 210 m$^2$ | 2,260 sq ft | |
| sextans | 4,800 | 1⁄6 | 421 m$^2$ | 4,530 sq ft | |
| quadrans | 7,200 | 1⁄4 | 631 m$^2$ | 6,790 sq ft | |
| triens | 9,600 | 1⁄3 | 841 m$^2$ | 9,050 sq ft | |
| quincunx | 12,000 | 5⁄12 | 1,051 m$^2$ | 11,310 sq ft | |
| semis | 14,400 | 1⁄2 | 1,262 m$^2$ | 15,380 sq ft | = actus quadratus |
| septunx | 16,800 | 7⁄12 | 1,472 m$^2$ | 15,840 sq ft | |
| bes | 19,200 | 2⁄3 | 1,682 m$^2$ | 18,100 sq ft | |
| dodrans | 21,600 | 3⁄4 | 1,893 m$^2$ | 20,380 sq ft | |
| dextans | 24,000 | 5⁄6 | 2,103 m$^2$ | 22,640 sq ft | |
| deunx | 26,400 | 11⁄12 | 2,313 m$^2$ | 24,900 sq ft | |
| jugerum | 28,800 | 1 | 2,523 m$^2$ | 27,160 sq ft | |
| Except where noted, based on Millar (1745). 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 pes (Roman 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 (5.7 imp gal; 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 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 and 580 ml (17–20 US fl oz).
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). 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 | 2.84 gal | 2.94 gal |
| Except where noted, based on Smith (1851). 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. 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.
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" |
| 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" |
| 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 | | 328.9 g | 11.60 oz 0.725 lb | lit. "balance" |
| Except where noted, based on Smith (1851). 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 | 1⁄48 uncia | 0.57 g | 8.8 gr 0.020 oz | lit. "obol", from the Greek word for "metal spit" |
| scrupulum | scruple | 1⁄24 uncia | 1.14 g | 17.6 gr 0.040 oz | lit. "small pebble" |
| semisextula or dimidia sextula | | 1⁄12 uncia | 2.28 g | 35.2 gr 0.080 oz | lit. "half-sixth", "little sixth" |
| sextula | sextula | 1⁄6 uncia | 4.57 g | 70.5 gr 0.161 oz | lit. "little sixth" |
| 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 | 1⁄2 uncia | 13.7 g | 211 gr 0.483 oz | lit. "half-twelfth" |
| uncia | Roman ounce | | 27.4 g | 423 gr 0.967 oz | "a twelfth" |
| Except where noted, based on Smith (1851). Metric equivalents are approximate, converted at 1 libra = 328.9 g . ||||||

## Time
### Years

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 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, based on the supposed birth year of Jesus.
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 (i.e. 97 leap years in every 400) to more closely approximate the length of the tropical year.

### Weeks

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.

### Hours

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 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).

## Unicode

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 Official Unicode Consortium code chart (PDF) :
| | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | A | B | C |
| U+1019x | 𐆐 | 𐆑 | 𐆒 | 𐆓 | 𐆔 | 𐆕 | 𐆖 | 𐆗 | 𐆘 | 𐆙 | 𐆚 | 𐆛 | 𐆜 |
| U+101Ax | 𐆠 | | | | | | | | | | | | |
| U+101Bx | | | | | | | | | | | | | |
| U+101Cx | | | | | | | | | | | | | |
| Notes 1.^ As of Unicode version 16.0 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