The most important thing about "acceptability" of errors is that they don't disrupt the reader. That means that some errors weigh heavier than others, even if you have the same number of typos.
Consider, for example, the fact that most Americans these days get "you're" vs. "your" drilled into their head during school. It creates a bias towards the focus on these mistakes, and so I would guess that a lot more readers would notice the misuse in a sentence a lot quicker than the intentional singular use of the word 'head' earlier in this paragraph. You should be cautious of these.
Next, there's the pacing of the book itself. If you're in the middle of a gripping action sequence, a light error will probably be completely skipped over by many readers even if they see it, because they're so engaged with the scene, but a hard error will probably stop them in their tracks and make them pause and re-read the whole sentence. This disrupts the flow of your story and can really detract from the strength of a writer.
Consider the frequency of the error that occurs.
There was one book that had a silly typo -- let's say it was allusion instead of illusion (I'm going to remember what it is later). The first time I noticed it, I gave a soft snort and continued reading, my opinion of the book generally unaltered. Typos happen. However, the author persisted to use the same word, maybe once every two chapters. Every single time, they used the wrong word. It drove me absolutely bonkers, because there was no particular reason for them to be using the word all the time in the first place. I don't remember what book it was, and I actually enjoyed both the characters and the plot, but every time I open it up and get to that first typo I groan. This book again.
My general opinion is that as long as your typos are 'soft' and your book is 300 pages long, a reader can probably choose to ignore them if you have fewer than 30. If the plot/characters aren't good, they probably won't bother. On the other hand, if you only have 5 errors in a 300 page book, even though the reader may notice them, they won't remember them when thinking about the book as a whole.
The hard errors probably will be remembered regardless, but if you only have one or two (and your book is otherwise well-written), your readers will probably choose to ignore them. Just make sure they don't take place during critical scenes.