| Millennium: | 4th Millennium BC |
|---|---|
| Centuries: | 39th cent. BC – 38th cent. BC – 37th cent. BC |
| Decades: | 3810s BC 3800s BC 3790s BC – 3780s BC – 3770s BC 3760s BC 3750s BC |
| Years: | 3783 BC 3782 BC 3781 BC – 3780 BC – 3779 BC 3778 BC 3777 BC |
| Gregorian calendar | 3780 MMMDCCLXXX |
| Ab urbe condita | 4533 |
| Armenian calendar | 3229 ԹՎ ՎՄԻԹ |
| Assyrian calendar | 8530 |
| Bahá'í calendar | 1936–1937 |
| Bengali calendar | 3187 |
| Berber calendar | 4730 |
| British Regnal year | N/A |
| Buddhist calendar | 4324 |
| Burmese calendar | 3142 |
| Byzantine calendar | 9288–9289 |
| Chinese calendar | 己未年 (Earth Goat) 6476 or 6416 — to — 庚申年 (Metal Monkey) 6477 or 6417 |
| Coptic calendar | 3496–3497 |
| Discordian calendar | 4946 |
| Ethiopian calendar | 3772–3773 |
| Hebrew calendar | 7540–7541 |
| Hindu calendars | |
| - Vikram Samvat | 3836–3837 |
| - Shaka Samvat | 3701–3702 |
| - Kali Yuga | 6880–6881 |
| Holocene calendar | 13780 |
| Igbo calendar | 2780–2781 |
| Iranian calendar | 3158–3159 |
| Islamic calendar | 3255–3256 |
| Japanese calendar | Heisei 1792 (平成１７９２年) |
| Javanese calendar | 3767–3768 |
| Juche calendar | 1869 |
| Julian calendar | Gregorian minus 26 days |
| Korean calendar | 6113 |
| Minguo calendar | ROC 1869 民國1869年 |
| Nanakshahi calendar | 2312 |
| Thai solar calendar | 4323 |
| Unix time | 57118089600–57149711999 |
The year 3780 BC