First, how big is a brand new empty Git directory (.git)?

$ git init
Initialized empty Git repository in /home/dave/tmp/foo/.git/

$ du -sb .git
64828	.git

(The du options are: s to summarize and b to display bytes.)

Now I’m going to make a bunch of tiny files in directories with a pair of nested shell loops:

$ for d in {1..5};do
    mkdir $d;
    for f in {1..50};do
        echo foo > $d/$f;
    done;
done

Now I have 250 files in 5 directories containing the string "foo":

$ ls
1  2  3  4  5
$ cat 2/45
foo

$ git add .
$ git commit -m 'initial commit'

Let’s see how big .git is now:

The commit has added about 47 Kb to the initial blank repo.

Aside: I calculated this in the geekiest way I could think of, using the standard Unix command dc, the arbitrary precicision reverse-polish notation desk calculator (note that 'p' is the print command so we can see the result!):

$ dc -e '112468 64828 - p'
47640

Now I’ll make one tiny change to one file and commit it:

$ echo bar > 1/1
$ git commit -am 'changed 1/1'

$ du -sb .git
129613
$ dc -e '129613 112468 - p'
17145

So that’s 17 Kb to store about 3 bytes of changes to my repo.

Where is that weight coming from?

I’m gonna do another little commit. Here’s what it looks like before:

$ du -b .git
4096	.git/objects/info
4096	.git/objects/pack
4115	.git/objects/25
4155	.git/objects/7b
4225	.git/objects/af
4115	.git/objects/57
4271	.git/objects/07
4177	.git/objects/61
4255	.git/objects/bb
4299	.git/objects/a8
45900	.git/objects
4336	.git/info
4096	.git/refs/tags
4137	.git/refs/heads
12329	.git/refs
4096	.git/branches
4411	.git/logs/refs/heads
8507	.git/logs/refs
12918	.git/logs
27538	.git/hooks
129613	.git

Then I modify file 1/1 again to contain the string 'baz' and commit that.

4096	.git/objects/info
4096	.git/objects/pack
4115	.git/objects/25
4253	.git/objects/81 <-- new 4 Kb
4155	.git/objects/7b
4225	.git/objects/af
4115	.git/objects/57
4271	.git/objects/07
4177	.git/objects/61
4302	.git/objects/fc <-- new 4 Kb
4255	.git/objects/bb
4115	.git/objects/76 <-- new 4 Kb
4299	.git/objects/a8
4177	.git/objects/92 <-- new 4 Kb
62747	.git/objects
4336	.git/info
4096	.git/refs/tags
4137	.git/refs/heads
12329	.git/refs
4096	.git/branches
4561	.git/logs/refs/heads <-- added 0.1 Kb
8657	.git/logs/refs
13218	.git/logs
27538	.git/hooks
146759	.git

That’s 4 new objects for a single-file commit.

Although these files are all zlib compressed data, I figured out that git show will show the value of any object by hash identifier, not just commits!

So to view these objects, I did:

$ ls .git/objects/81
b1a9d27494b40679d612b96bb6acaac83afa9c
$ git show 81b1a9d27494b40679d612b96bb6acaac83afa9c

81… is my actual commit
fc… is the tree file for the changed directory 1., listing all of the files in that directory (1 through 50).
76… is the actual contents of file 1/1 (which is now the string 'baz')
92… is another tree for the root directory of the repo

That makes sense. There’s a commit, two trees, and one file.