A cubit is an ancient unit of length based on the distance from the elbow to the tip of the middle finger. Its length varied among cultures and over time but generally ranged between about 17.5 inches (44.5 cm) and 21 inches (53 cm).
- The common cubit is often taken as approximately 18 inches (457 mm), equivalent to 6 palms or 2 spans
- Ancient Egyptian royal cubits were about 52.2 to 52.9 cm (20.6 to 20.8 inches)
- Biblical or Hebrew cubits varied; some sources estimate around 17.5 inches (44.5 cm) for a short cubit and about 20.4 to 21.5 inches (52 to 54.5 cm) for a long or royal cubit
- The ancient Roman cubit could be as long as 120 cm (3 ft 11 in), though that was an outlier
In summary, a cubit typically measures roughly 18 to 21 inches (45 to 53 cm), with the royal cubit being the longer standard used in large-scale constructions like the Egyptian pyramids and biblical structures
