Way 1 · best default
I'm exhausted
Clearly more than tired. Safe with friends, family and your boss.
Examples
I'm exhausted. I've been on my feet since six this morning.
Sorry if I'm quiet, I'm completely exhausted after the trip.
In a conversation
A: You look like you need a sit-down.
B: I do. I'm exhausted, the baby was up all night.
Common mistake
Not: I'm very exhausted.
Say: I'm completely exhausted.
"Exhausted" is already extreme, so English uses "completely" or "absolutely", not "very".