| 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 |
| Bahá'í calendar | -1200 – -1199 |
| Bengali calendar | 51 |
| Berber calendar | 1594 |
| 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 | |
| - Bikram Samwat | 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 |
| Thai solar calendar | 1187 |