|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|
|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|
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 conquer Rhodes, which has refused him armed support against Ptolemy. He shows ingenuity in devising new siege engines in his unsuccessful attempt to reduce the city. Among his creations are a battering ram 60 metres long and requiring 1,000 men to operate it and a wheeled siege tower named "Helepolis" (or "Taker of Cities") which stands 40 metres tall and 20 metres wide and weighs 180 tons. This siege of Rhodes earns Demetrius the title Poliorcetes ("the City Besieger").
- 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.