For the unit of information, see qubit. For the bone, see ulna.
Cubit is the name for any one of many units of measure used by various ancient peoples, based on the distance between the tip of the middle finger and the elbow on an average person or a similar forearm-based measurement. This definition was often made more specific when a cubit-using culture adopted more standardized measurements. Some cubits are still used today, especially for religious purposes (such as in Judaism).
The cubit is among the first recorded units of length used by an ancient people. From around 1950 BC, the copper bar cubit of Nippur defines the Sumerian cubit as 517.2 mm (20.36 inches) and is the earliest known length standard.
While no standard rule exists from Old Kingdom Egypt, it has been securely estabished from surviving architectural evidence that a standard measure was employed as early as c. 2750 BC at Saqqara. From the evidence this is widely accepted to have been 523.5 to 524 mm (20.61 to 20.63 in) in length, and was subdivided into 7 palms of 4 digits, giving a 28 part measure in total. A shorter rule of 6 palms may also have been employed, but based on the same 7 part standard. The basic length was probably originally based on the length of the forearm from the elbow to the middle finger tip. Standard Egyptian cubits survive from later dynasties.
Many other cultures used cubits as well. Persian cubits were 52–64 cm (20–25 in), the Greek πε&khi;υα (pechua) was some 47.4 cm (18.7 in), the Roman cubitus was 44.46 cm (17.50 in), the Arabic arsh 48–64 cm (19–28 in), and the אַמָּה (ama) used for Jewish religious purposes today is considered to be some 46–61 cm (18–24 in).
See also