Cubit

A cubit is the first recorded unit of length and was one of many different standards of measurement used through history. It was originally based on measuring by comparing to one's forearm length.

Cubits were employed through Antiquity, the Middle Ages up to the Early Modern Times, especially for measuring cords and textiles, but also for timbers, stone and volumes of grain.

The Egyptian hieroglyph for the unit shows the symbol of a forearm, but it was rather longer than any actual forearms. The Egyptian cubit was not subdivided into centimetres or inches, but into palms and digits. The Egyptian cubit was subdivided into 7 'palms' of 4 'digits', making 28 parts in all, and was between 52.3 and 52.4cm in length.

The distance between thumb and another finger to the elbow on an average person measures about 24 digits or 6 palms or 1½ feet. This is about 45 cm or 18 inches. This cubit is sometimes referred to as a "natural cubit" of 1½ feet and was used in the Roman system of measures and in different Greek systems.

Over time, various cubits and variations on the cubit have measured:

From late Antiquity, the Roman ulna, a four-foot cubit (about 120 cm) is also attested. This length is the measure from a man's hip to the fingers of the outstretched opposite arm.

The English yard could be considered to be a type of cubit, measuring 12 palms, ~90 cm, or 36 inches (3.00 ft). This is the measure from the middle of a man's body to his fingers, always with outstretched arm. The English ell is essentially a kind of great cubit of 15 palms, 114 cm, or 45 inches (3.75 ft).

History of the different cubits

The Egyptian royal cubit and Sumerian Nippur cubit

Old Egyptian geometers could calculate the square root of two from the value of the hypotenuse of a cubit. This well-attested old Egyptian unit was known as the "construction remen" and used a good approximation: $2\; \backslash times\; 20\; /\; 28\; \backslash ge\; \backslash sqrt\; 2$.

Other important cubits

The Greek pēchys () was also a 24-digit cubit. So, the kyrēnaikos pēchys ("Cyrenaican cubit") measured about 463.1 mm and the metrios pēchys ("middle cubit") about 474.2 mm; respectively roughly and Roman cubits. Other Greek cubits based on different digit measures of other city-states are less important. The Greek 40-digit-measure, called bēma, corresponds to the Latin gradus, the step or half-a-pace.

The guard cubit (Arabic: ) measured about 555.6 mm; of the Roman cubit. Therefore: 96 guard cubits ≈ 120 Roman cubits ≈ 175 English feet.

The Arabic nil cubit (or black cubit) measured about 540.2 mm. This means 28 (later called) Greek digits of the kyrēnaikos pēchys ≈ of a Roman foot or just 308.7 mm. Thus 175 Roman cubits ≈ 144 black cubits.

The Mesopotamian cubit measured about 533.4 mm, Roman cubit. Thus, 20 Mesopotamian cubits ≈ 24 Roman cubits ≈ 35 English feet.

The Babylonian cubit (or cubit of Lagash) measured about 496.1 mm. Also a Babylonian trade cubit existed, nine-tenths of the normal cubit, i.e. 446.5 mm. The Babylonian cubit is of the royal cubit. 160 Babylonian trade cubits ≈ 144 Babylonian cubits ≈ 135 Egyptian royal cubits. (The royal cubit ≈ 529.2 mm. See above.)

The (Pergamon) cubit 520.9 mm or of the Roman cubit. The (Salamis) cubit 484.0 mm or of the Roman cubit. The (Persia) cubit of about 500.1 mm or of the Roman cubit, which is also of the guard cubit.

See also

Notes