Calculate filtered document's size

Hi all,
Is there a way to calculate the amount of filtered documents size inside a specific index?
I mean, in a daily log index I would like to know the index total size is divided.

I found the mapper-size plugin but I am not really sure it can help me.
is there any tip?

That will give you a raw idea. It will actually give you the size of the _source field, which is your JSON content. Not exactly the size on disk took by the document.