When I was a kid, me and my family drove down Sweden, down to the southernmost city in Norway, and back up to northern Norway. I'm not sure how long that was because we took detours several times, but thinking back, it felt like we drove for weeks. So that's what, 3000-4000 kilometers.
I haven't driven very far myself. I just never had anywhere to drive. Going by plane or boat beats driving. So maybe 4-500km in one go.