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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.

Length

  Modern metrologists have found the Roman foot to be ¹⁶⁄₂₈ of the Nippur cubit.

Notes

1. From late Antiquity the Roman foot was sometimes divided into unciae comprising 12 equal parts.
   The ancient digit measure, however, largely dominated before the beginning of the Middle Ages.
2. The value of the historical Roman foot scientifically obtained through modern statistical methods is 296.2 mm ± 0.5 mm, or about (296.2 ± 0.17%) mm (cf. Rottländer, Tübingen, Germany). The table above is based on this value, but rounded to the millimetre precision for the foot.
3. The widely accepted ratio between the Roman foot and the English foot is 36:35. That is, 36 Roman feet to 35 English feet, making the Roman foot slightly shorter than its modern equivalent. The latter one is 16/28 Mesopotamian cubit and the ratio between this one and the Roman cubit is 20:24. If the present English foot is taken as for reference, the Roman foot should be 296 1/3 mm or approximately 11.65 English inches. That is within the margin obtained by R.C.A. Rottländer (see references).
4. A Roman foot can be visualised as being approximately equal to the height of an A4 sheet of paper (297 mm). This comparison, although descriptive, is +0.27% out of the range given above.

Area

The Roman acre is the squared Roman arpent, 120 pedes by 120 pedes. This equals 14 400 square feet or about 0.126 hectares.

The Romans also had a unit of area called a quinaria, which was used to measure the cross-sectional area of pipes. One quinaria was considered to be roughly 4.2 cm².

Volume

Liquid measures

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

Dry measures

Bronze modius (4th cent. CE)

Like the jar, the Roman bushel or "quadrantal" is one cubic foot. It is almost 26.027 litres. One-third of a quandrantal is a Roman peck.

Mass and coins

The Roman pound is exactly three quarters of the Greek mine.
Thus the Greek and Roman drachm is related by the ratio 32 to 25.

One and a half ounces was called by Romans "sescuncia". Some of these nouns were used to designate Roman bronze coins.

Time

The Julian calendar was introduced in 45 BC replacing the earlier Roman calendar. In the Julian calendar, an ordinary year is 365 days long, a leap year is 366 days long, and every fourth year is a leap year. 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.

References

1. ^ Accuracy of length units Google translation of http://vormetrische-laengeneinheiten.de/html/genauigkeit.html by Rolf C. A. Rottländer, Rottenburg / Köln

Sources

• Vormetrische Längeneinheiten by Rolf C. A. Rottländer, Rottenburg / Köln (also see Search-Engine).
• Recovery of the Ancient System Foot/Cubit/Stadion by Dieter Lelgemann, acting Director of the Institute for Geodesy and Geo-Information Technology, TU Berlin.
• On the Ancient Determination of Meridian Arc Length by Eratosthenes of Kyrene Dieter Lelgemann, WS – History of Surveying and Measurement, Athens, Greece, May 22-27, 2004.
• Knobloch, Eberhard, Dieter Lelgemann und Andreas Fuls: "Zur hellenistischen Methode der Bestimmung des Erdumfangs und zur Asienkarte des Klaudios Ptolemaios.", published in zfv (Zeitschrift für Geodäsie, Geoinformation und Landmanagment) 128. Jahrgang, Heft 3/2003, S. 211-217.
• Reference draws of the Nippur Cubit at Florencetime.net.
• Proposal to Add Ancient Roman Weights and Monetary Signs to UCS (Universal Character Set)

See also

• Systems of measurement
• History of measurement
• Units of measurement