|Millennium:||1st millennium BC|
|305 BC by topic|
|Gregorian calendar||305 BC|
|Ab urbe condita||449|
|Ancient Egypt era||XXXIII dynasty, 19|
|- Pharaoh||Ptolemy I Soter, 19|
|Ancient Greek era||118th Olympiad, year 4|
|Balinese saka calendar||N/A|
|Chinese calendar||乙卯年 (Wood Rabbit)|
2392 or 2332
— to —
丙辰年 (Fire Dragon)
2393 or 2333
|Coptic calendar||−588 – −587|
|Ethiopian calendar||−312 – −311|
|- Vikram Samvat||−248 – −247|
|- Shaka Samvat||N/A|
|- Kali Yuga||2796–2797|
|Iranian calendar||926 BP – 925 BP|
|Islamic calendar||954 BH – 953 BH|
|Minguo calendar||2216 before ROC|
|Seleucid era||7/8 AG|
|Thai solar calendar||238–239|
−178 or −559 or −1331
— to —
−177 or −558 or −1330
Year 305 BC was a year of the pre-Julian Roman calendar. At the time, it was known as the Year of the Consulship of Megellus and Augurinus (or, less frequently, year 449 Ab urbe condita). The denomination 305 BC 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.
- Seleucus, former officer of Alexander the Great, considers himself emperor of Persia. He attempts to recover lands taken by Chandragupta that had been a part of Alexander's Empire. Seleucus establishes Seleucia on the Tigris River as his capital.
- Antigonus I Monophthalmus sends his son Demetrius to initiate the Siege of Rhodes, as the city has refused him armed support against Ptolemy.
- The Roman consuls, Marcus Fulvius Curvus Paetinus and Lucius Postumius Megellus, decisively defeat the Samnites in the Battle of Bovianum to end the Second Samnite War.
- Zou Yan, Chinese philosopher (d. 240 BC)