How it is possible to calculate earning?

I am new on AdSense.
I am looking for basic question how are calculated earnings.
It is possible to calculate it?
If yes how it is calculated?

In my report I see CTR column, CPM, but I am really not sure what these columns means.
I found that CPM is "Cost per 1000 impressions". Does it means if I have no click on ads but I have 2000 impressions
I will earn 2*CPM. Are page impressions cumulative, or they resets them each day?
CTR - Click through rate it looks like clicks/page impressions, it .

It looks like it is not predictable how much I earn from every click.

You are right it is not predictable as campaigns/competition change.

The CPM that you see in your adsense stats is based on the actual earnings.

And are page impressions reseted each day, or are they cumulative for CPM earning?

No page impressions are reseted every day

Thanks, now I know more.

A single click can make anywhere between $0.01 and several $. Nothing to predict the earnings per click though, I have seen $10 in one day and only $1 the next (with way more clicks on the second day :( ) a lot of times...

lets say you made 500 impressions and got 5 clicks and you earned $2, your ctr is 1% because 1% of 500 is 5, and your cpm is $4 because google estimates that since you earned $2 with 500 impressions, you might earn $4 with 1000 impressions.

heres what the AdSense Help Center says about CPM:

"Cost per 1000 impressions. From a publisher's perspective, CPM is a useful way to compare revenue across different channels and advertising programs. It is calculated by dividing total earnings by the number of impressions in thousands. For example, if a publisher earned $180 from 45,000 impressions, the CPM would equal $180/45, or $4.00. However, please keep in mind that eCPM is a reporting feature that does not represent the actual amount paid to a publisher."