The standard spacing for a tab is 8 characters.
I prefer to view that as 4 characters in my editors and console. I can easily change this default behavior on console with the
This actually has nothing to do with
git diff actually renders a tab, which is later converted by your terminal emulators (for instance,
gnome-terminal) to spaces.
Go to the preference of your terminal emulator to change that setting.
Also, git may use a pager, so you might want to configure it like that:
git config --global core.pager 'less -x1,5'
More information here: setting tabwidth to 4 in git show / git diff