Year 303 (CCCIII) was a common year starting on Friday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Valerius and Valerius (or, less frequently, year 1056 Ab urbe condita). The denomination 303 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.

.303 may refer to:

• .303 British, a rifle cartridge
• .303 Savage, a rifle cartridge
• Lee–Enfield rifle
• .303 (film), a short film