The diameter of a penny is 19.05 millimeters (0.748 inches). This measurement has remained consistent since the penny was first introduced in its current form in 1792.
The size of the penny is important for a few reasons. First, it ensures that the coin can be easily handled and distinguished from other denominations. Second, the dimensions help maintain standardization in currency, allowing machines like coin sorters and vending machines to recognize and accept pennies correctly. Understanding the physical measurements of coins also provides insight into their design and production processes.