The cubit is an archaic unit of length based on the length of the forearm from the elbow to the tip of the middle finger. Cubits of various lengths were employed in many parts of the world in antiquity, during the Middle Ages and as recently as Early Modern Times. The cubit has also been expressed as "any of various ancient units of length based on the length of the forearm from the elbow to the tip of the middle finger and usually equal to almost 18 inches (46 centimeters)". It is still used in hedge laying. The length of the forearm being frequently used to determine the interval between stakes placed within the hedge.
The Egyptian royal cubit and Sumerian Nippur cubit 
Among the various cubits that have been identified in history the Egyptian and Sumerian Nippur (Biblical) cubits figure prominently.
- Egyptian royal cubit: 7 palms × 4 fingers = 28 digits
- Sumerian Nippur cubit: 6 palms × 4 fingers = 24 digits
The earliest attested standard measure is from the Old Kingdom pyramids of Egypt and was called the royal cubit (mahe). The royal cubit was 523 to 529 mm (20.6 to 20.8 in) in length, and was subdivided into 7 palms of 4 digits each, for a 28-part measure in total. Evidence for the royal cubit unit is known from Old Kingdom architecture, from at least as early as the construction of the Step Pyramid of Djoser from around 2,700 B.C.
The Egyptian hieroglyph for the cubit shows the symbol of a longer than normal forearm. According to the Ancient Egyptian units of measurement, the Egyptian Royal cubit was subdivided into 7 palms of 4 fingers/digits each; surviving cubit rods are between 52.3 and 52.9 cm (20.6 to 20.8 inches) in length.
In 1916, during the last years of Ottoman Empire and in the middle of WWI, the German Assyriologist Eckhard Unger found a copper-alloy bar while excavating at Nippur. The bar dates from c. 2650 BCE and Unger claimed it was used as a measurement standard. This irregularly formed and irregularly marked graduated rule supposedly defined the Sumerian cubit as about 518.6 mm.
Near Eastern or Biblical cubit 
The Near Eastern or Biblical cubit is usually estimated as approximately 18 inches for conversion into English units. Editors' comments in many editions of the Torah, Tanakh and Christian Bibles reflect this.
The first mention of cubits in the Hebrew Bible appears in Genesis in reference to Noah's ark: "the length of the ark three hundred cubits, its width fifty cubits, and its height thirty cubits." (NRSV) Estimating the length of this cubit as approximately 18 inches yields dimensions of approximately 450 × 75 × 45 feet.  Measurement in cubits appears in the Hebrew Scriptures for a number of other objects as well, including the Tabernacle and Ark of the Covenant (Exodus 27, etc.).
Other systems 
Other measurements based on the length of the forearm are the Indian Hasta and Thai sok. A traditional measure in Karnataka commonly used by flower sellers is the "Mola" which is equal to a cubit and "Maaru" which is equal to a fathom.
Cubit arm in heraldry 
A cubit arm in heraldry may be dexter or sinister. It may be vested (with a sleeve) and may be shown in various positions, most commonly erect, but also fesswise (horizontal), bendwise (diagonal) and is often shown grasping objects. It is most often used erect as a crest, for example by the families of Poyntz of Iron Acton, Rolle of Stevenstone and Turton.
See also 
- Ancient Mesopotamian units of measurement
- Anthropic units
- History of measurement
- Systems of measurement
- Units of measurement
- Cassell's Latin Dictionary
- Oxford English Dictionary, Second edition, 1989; online version September 2011. s.v. "cubit"
- Dieter, Arnold (1991). Building in Egypt: pharaonic stone masonry. Oxford: Oxford University Press. ISBN 978-0-19-506350-9. p.251.
- Sacred Geometry p. 31 by Stephen Skinner (Sterling, 2006)
- Lauer, Jean Philippe (1931). "Étude sur Quelques Monuments de la IIIe Dynastie (Pyramide à Degrés de Saqqarah)". Annales du Service des Antiquités de L'Egypte IFAO 31:60 p. 59
- Acta praehistorica et archaeologica Volumes 7–8. Berliner Gesellschaft für Anthropologie, Ethnologie und Urgeschichte; Ibero-Amerikanisches Institut (Berlin, Germany); Staatliche Museen Preussischer Kulturbesitz. Berlin: Bruno Hessling Verlag, 1976. p. 49.
- the Chumash Stone Edition footnotes to Gen 6:15-16
- "Figuring a cubit to be about 18 inches"—footnote to Gen. 6:15 in The Torah edited by W. G. Plaut (Jewish Publication Society 1962, 1967 / Union of American Hebrew Congregations 1981)
- The New American Bible notes to Gen 6:15
- Arnold, Dieter (2003). The Encyclopaedia of Ancient Egyptian Architecture. Taurus. ISBN 1-86064-465-1.
- Petrie, Sir Flinders (1881). Pyramids and Temples of Gizeh.
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- Measurements of the Nippur Ell, now in a museum in Istanbul (Turkey).