In the U.K.: "I'm knackered!"

I can only try to guess at Matthew’s options. ‘Knackered’ , as Charlie says, is standard in the U.K. [In former times, when a horse was no longer fit for work, it was sent to the ‘knacker’s yard’ to be slaughtered and its parts used for other purposes ; you can see how ‘knackered’ came to acquire its slang meaning] ‘Whacked’ could also be used colloquially for ‘very tired’ or ‘exhausted’. ‘Pooped’ is one I’m not familiar with.

There are probably dozens of ways to say exhausted in English. My favorites are wiped out, worn out and tuckered out. They’re all probably more American English than British English.

The more colloquial rendition of knackered would be I'm cream-crackered (exhausted), which also jogs my memory of another saying built around food: "I'm toast," often used to express anticipated failure (e.g. If I don't complete my homework, I am toast." Hope you enjoy the tangent.

I'm a southern American and in addition to some of the ones mentioned, I sometimes say "I'm done" or "I've hit the wall", but the last one is more work related. It's like when you are at work and you just can't focus or be productive anymore and the best thing to do is leave and start fresh the next day. There also is "out of gas" but that one might be regional and it can also be slang for "out of luck" here in the south so be careful. Hope this helps!