|Millennium:||1st millennium BC|
|Centuries:||5th century BC – 4th century BC – 3rd century BC|
|Decades:||330s BC 320s BC 310s BC – 300s BC – 290s BC 280s BC 270s BC|
|Years:||307 BC 306 BC 305 BC – 304 BC – 303 BC 302 BC 301 BC|
|304 BC by topic|
|Gregorian calendar||304 BC|
|Ab urbe condita||450|
|Ancient Egypt era||XXXIII dynasty, 20|
|- Pharaoh||Ptolemy I Soter, 20|
|Ancient Greek era||119th Olympiad (victor)¹|
|Chinese calendar||丙辰年 (Fire Dragon)
2393 or 2333
— to —
丁巳年 (Fire Snake)
2394 or 2334
|Coptic calendar||−587 – −586|
|Ethiopian calendar||−311 – −310|
|- Vikram Samvat||−247 – −246|
|- Shaka Samvat||N/A|
|- Kali Yuga||2798–2799|
|Iranian calendar||925 BP – 924 BP|
|Islamic calendar||953 BH – 952 BH|
|Minguo calendar||2215 before ROC
|Seleucid era||8/9 AG|
|Thai solar calendar||239–240|
|Wikimedia Commons has media related to 304 BC.|
Year 304 BC was a year of the pre-Julian Roman calendar. At the time, it was known as the Year of the Consulship of Sophus and Severrio (or, less frequently, year 450 Ab urbe condita). The denomination 304 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.
- The siege of Rhodes ends after a year as Demetrius Poliorcetes meets with obstinate resistance from the citizens of Rhodes who are supported by Ptolemy (thereby earning Ptolemy the title of Soter (Saviour)). Antigonus then concludes a peace treaty and an alliance with the island state, guaranteeing it autonomy and neutrality in his conflicts with Ptolemy.
- Cassander invades Attica and besieges Athens. Demetrius Poliorcetes drives Cassander out of central Greece and liberates Athens. In return, the Athenians bestow on him a new religious honour, synnaos ("having the same temple") of the temple of the goddess Athena.
- The second Samnite war formally ends with a peace agreement in which the Samnites obtain peace on terms that are severe but not as crushing as those agreed by the Romans with the Etruscans four years earlier. Under the peace, Rome gains no territory, but the Samnites renounce their hegemony over Campania. Rome is also successful in ending the revolts amongst the tribes surrounding Roman territory.
- The tyrant Agathocles takes on the title of King of Sicily. He extends his influence into southern Italy and the Adriatic.
- Ashoka the Great, Indian emperor and ruler of the Maurya Empire in present-day eastern India 273–232 BC (d. 232 BC)