What This File Is Actually Made Of ENTROPY
The rule is that entropy above 7.0 means packed. A ZIP, a PNG and a packed executable are the same statistical object, so no threshold can separate them.
The file
Any file at all, of any type. It is read by this page on this device and no part of it is sent anywhere — which is what makes this usable on something you are not permitted to upload, which is most of what anybody wants to measure.
What it measures
Across the file
Start of the file on the left, end on the right, eight bits at the top. The dashed line is 7.0 — it is drawn so it can be seen not to mean much, rather than left out of the argument. A packed executable is usually a plain stub then a dense blob, with the join visible. An archive is dense from end to end. A document with one encrypted attachment is ordinary with a dense patch in it. All three can report the same average.
What that is consistent with
Consistent with, not equal to. Several quite different things produce the same figures, and the page lists them rather than choosing between them, because choosing would mean claiming to know something the measurement does not contain.
The working
Questions people ask about ENTROPY