| Flag | Code | Country | Time Difference (GMT) | Group | Comment | Internet Code |
 | 855 | CAMBODIA (Kingdom of) | 7 | | | kh |
 | 237 | CAMEROON (Republic of) | 1 | BCW | | cm |
 | 1613 | CANADA | -3.5 to -8 | NATO, BCW | This is a hypothetical code - List of all codes | ca |
 | 34 | Canary Islands | 1 | SPAIN | | es |
 | 238 | CAPE VERDE (Republic of) | -1 | | | cv |
 | 1473 | Carriacou | -4 | WIN | GRENADA | gd |
 | 1345 | CAYMAN ISLANDS | -5 | BRD | | ky |
 | 236 | CENTRAL AFRICAN REPUBLIC | 1 | | | cf |
 | 235 | CHAD (Republic of) | 1 | | | td |
 | 44 | Channel Islands | 0 | UKD | Jersey - Guernsey - Alderney - Herm - Sark | |
 | 64 | Chatham Island | 12 | NZ | NEW ZEALAND | nz |
 | 56 | CHILE | -4 | | | cl |
 | 86 | CHINA (Peoples Republic of) | 8 | | | cn |
 | 61 | Christmas Island | 7 | AET | Changed from 6724 to 61964 | cx |
| 61 | Cocos Islands | 6.5 | AET | Changed from 6722 to 61962 | cc |
 | 57 | COLOMBIA (Republic of) | -5 | | | co |
 | 269 | COMOROS (Islamic Federal Republic of the) | 3 | | Country code shared with Mayotte | km |
 | 242 | CONGO (Republic of the) | 1 | | | cg |
 | 682 | COOK ISLANDS | -11.5 | | | ck |
| | Coral Sea Islands | | AET | | |
 | 506 | COSTA RICA | -6 | | | cr |
 | 225 | COTE D'IVOIRE (Republic of) | 0 | | Also known as Ivory Coast | ci |
 | 385 | CROATIA (Republic of) | 1 | EUC | | hr |
 | 53 | CUBA | -5 | | | cu |
 | 599 | Curacao | -4 | | | |
| 90392 | CYPRUS (NORTH) | 2 | CYP | Cyprus 357 | |
 | 357 | CYPRUS (Republic of) | 2 | CYP, BCW, EU | Cyprus (North) 90392 | cy |
 | 420 | CZECH REPUBLIC | 1 | EU, NATO | | cz |
 | 44 | Wales | 0 | UK | | uk |