Count the number of commits on a Git branch

To count the commits for the branch you are on:

git rev-list --count HEAD

for a branch

git rev-list --count <branch-name>

If you want to count the commits on a branch that are made since you created the branch

git rev-list --count HEAD ^<branch-name>

This will count all commits ever made that are not on the branch-name as well.

Examples

git checkout master
git checkout -b test
<We do 3 commits>
git rev-list --count HEAD ^master

Result: 3

If your branch comes of a branch called develop:

git checkout develop
git checkout -b test
<We do 3 commits>
git rev-list --count HEAD ^develop

Result: 3

Ignoring Merges

If you merge another branch into the current branch without fast forward and you do the above, the merge is also counted. This is because for git a merge is a commit.

If you don't want to count these commits add --no-merges:

git rev-list --no-merges --count HEAD ^develop

To see total no of commits you can do as Peter suggested above

git rev-list --count HEAD

And if you want to see number of commits made by each person try this line

git shortlog -s -n

will generate output like this

135  Tom Preston-Werner
15  Jack Danger Canty
10  Chris Van Pelt
7  Mark Reid
6  remi

It might require a relatively recent version of Git, but this works well for me:

git rev-list --count develop..HEAD

This gives me an exact count of commits in the current branch having its base on master.

The command in Peter's answer, git rev-list --count HEAD ^develop includes many more commits, 678 vs 97 on my current project.

My commit history is linear on this branch, so YMMV, but it gives me the exact answer I wanted, which is "How many commits have I added so far on this feature branch?".