| Centuries: | 6th century · 7th century · 8th century |
| Decades: | 610s 620s 630s 640s 650s 660s 670s |
| Years: | 642 643 644 645 646 647 648 |
| 645 by topic | |
| Politics | |
| State leaders – Sovereign states | |
| Birth and death categories | |
| Births – Deaths | |
| Establishment and disestablishment categories | |
| Establishments – Disestablishments | |
| Gregorian calendar | 645 DCXLV |
| Ab urbe condita | 1398 |
| Armenian calendar | 94 ԹՎ ՂԴ |
| Bahá'í calendar | -1199 – -1198 |
| Bengali calendar | 52 |
| Berber calendar | 1595 |
| Buddhist calendar | 1189 |
| Burmese calendar | 7 |
| Byzantine calendar | 6153 – 6154 |
| Chinese calendar | 甲辰年十一月廿八日 (3281/3341-11-28) — to —
乙巳年十二月初八日(3282/3342-12-8) |
| Coptic calendar | 361 – 362 |
| Ethiopian calendar | 637 – 638 |
| Hebrew calendar | 4405 – 4406 |
| Hindu calendars | |
| - Bikram Samwat | 701 – 702 |
| - Shaka Samvat | 567 – 568 |
| - Kali Yuga | 3746 – 3747 |
| Holocene calendar | 10645 |
| Iranian calendar | 23 – 24 |
| Islamic calendar | 24 – 25 |
| Japanese calendar | |
| Korean calendar | 2978 |
| Thai solar calendar | 1188 |
Great Wild Goose Pagoda at Ci'en Temple, Xi'an, Shanxi, is first errected. Tang dynasty.