| Kaja (1) | | KAH-yah (Swedish, Estonian) | Norwegian, Danish, Swedish, Estonian, Slovene | |
| Kaja (2) | | KIE-ah (Polish) | Polish, Slovene | |
| Karel | | KAH-rəl (Dutch), KAH-rel (Czech) | Dutch, Czech, Slovene | |
| Karmen | | - | Slovene, Croatian | |
| Karol | | KAH-rawl (Polish) | Polish, Slovak, Slovene | |
| Karolina | | kah-raw-LEE-nah (Polish), kah-ro-LEE-nah (Swedish, German) | Polish, Swedish, Norwegian, Danish, Hungarian, Slovene, Croatian, Macedonian, Lithuanian, German | |
| Katarina | | kah-tah-REE-nah (German, Swedish) | German, Swedish, Norwegian, Danish, Hungarian, Croatian, Serbian, Slovene | |
| Katica | | - | Croatian, Slovene, Hungarian | |
| Katja | | KAHT-yah (German, Dutch) | German, Swedish, Norwegian, Danish, Dutch, Slovene | |
| Klara | | KLAH-rah (German, Russian, Polish) | Swedish, Norwegian, Danish, Icelandic, German, Russian, Ukrainian, Polish, Slovene, Croatian | |
| Klavdija | | - | Slovene | |
| Klemen | | - | Slovene | |
| Klementina | | - | Slovene, Croatian | |
| Konrad | | KAWN-raht (German, Polish) | German, Swedish, Norwegian, Danish, Polish, Slovene | |
| KriŠTof | | - | Slovene, Slovak | |