|Millennium:||1st millennium 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|
|Balinese saka calendar||N/A|
|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||2797–2798|
|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|
−177 or −558 or −1330
— to —
−176 or −557 or −1329
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 Saverrio (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.
- Demetrius shows ingenuity in devising new siege engines a wheeled siege tower named Helepolis (or "Taker of Cities") which stands 40 meters tall and 20 meters wide and weighs 180 tons.
- The Siege of Rhodes ends after a year.
- Demetrius Poliorcetes and the Rhodians came to a truce, with the agreement that the city should be autonomous, should keep its own revenue and the Rhodians should be allies of Antigonus unless he is at war with Ptolemy.
- 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, Indian emperor and ruler of the Maurya Empire in present-day Eastern India 273–232 BC (d. 232 BC)
- Erasistratus, Greek anotomist and physician (approximate date)
- Siculus, Diodorus. "91". Library. XX.
- Siculus, Diodorus. "99". Library. XX.
- Dupuy, R. Ernest; Dupuy, Trevor N. (1986). The Encyclopedia of Military History. New York: Harper & Row. p. 54. ISBN 0-06-181235-8.
- Dupuy, R. Ernest; Dupuy, Trevor N. (1986). The Encyclopedia of Military History. New York: Harper & Row. p. 59. ISBN 0-06-181235-8.