| Millennium: | 1st millennium |
|---|---|
| Centuries: | 6th century – 7th century – 8th century |
| Decades: | 610s 620s 630s – 640s – 650s 660s 670s |
| Years: | 641 642 643 – 644 – 645 646 647 |
| 644 by topic | |
| Politics | |
| State leaders – Sovereign states | |
| Birth and death categories | |
| Births – Deaths | |
| Establishment and disestablishment categories | |
| Establishments – Disestablishments | |
| Gregorian calendar | 644 DCXLIV |
| Ab urbe condita | 1397 |
| Armenian calendar | 93 ԹՎ ՂԳ |
| Assyrian calendar | 5394 |
| Bahá'í calendar | -1200–-1199 |
| Bengali calendar | 51 |
| Berber calendar | 1594 |
| English Regnal year | N/A |
| Buddhist calendar | 1188 |
| Burmese calendar | 6 |
| Byzantine calendar | 6152–6153 |
| Chinese calendar | 癸卯年十一月十六日 (3280/3340-11-16) — to —
甲辰年十一月廿七日(3281/3341-11-27) |
| Coptic calendar | 360–361 |
| Ethiopian calendar | 636–637 |
| Hebrew calendar | 4404–4405 |
| Hindu calendars | |
| - Vikram Samvat | 700–701 |
| - Shaka Samvat | 566–567 |
| - Kali Yuga | 3745–3746 |
| Holocene calendar | 10644 |
| Iranian calendar | 22–23 |
| Islamic calendar | 23–24 |
| Japanese calendar | |
| Korean calendar | 2977 |
| Minguo calendar | 1268 before ROC 民前1268年 |
| Thai solar calendar | 1187 |
Year 644 (DCXLIV) was a leap year starting on Thursday (link will display the full calendar) of the Julian calendar. The denomination 644 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.