How do I know the gzip compression level?

Given a gzip compressed file, how do I know what compression level (1-9) was used for it?

4 Answers

There is no way to directly determine gzip level .
The only way to determine it in my opinion is to gunzip the file and compressing it at different levels and then comparing the results with your existing file size.
I believe the default level is 6 so in most cases that should be your answer

5

It is stored in the header of file. To see it, use file command. For example:

$ file testfile.gz
testfile.gz: gzip compressed data, from Unix, last modified: Sun Sep 15 14:22:19 2013, max compression

Unfortunately there are only three possible values in the header: max speed (level 1), max compression (level 9) and "normal" (all other levels). But better than nothing!

4

gzip -l <filename> will give you the compression ratio, but there's no way of directly finding the compression level used.

1

There is no direct way of knowing it. It most probably 6 (the current default) or 9 (the best compression). you need to try and compare.

See

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