The "cubit" is an ancient unit of measurement for length that was historically used in various cultures, including ancient Egypt, Mesopotamia, and the Hebrew Bible. It was typically based on the length of a person's forearm from the elbow to the tip of the middle finger. As a result, the actual length of a cubit could vary from region to region and even from person to person.
In the United Kingdom and other parts of the world where the British imperial system was historically used, a cubit was typically defined as roughly 18 inches or about 45.72 centimeters. This is often referred to as the "British cubit."
However, it's important to note that the cubit is an ancient and non-standardized unit of measurement that has largely fallen out of use in modern times. Today, standardized units such as feet, meters, and inches are used for precise measurements, and the cubit is primarily of historical and cultural interest.