You need to add the path of your pip installation to your PATH system variable. By default, pip is installed to
C:\Python34\Scripts\pip (pip now comes bundled with new versions of python), so the path “C:\Python34\Scripts” needs to be added to your PATH variable.
To check if it is already in your PATH variable, type
echo %PATH% at the CMD prompt
To add the path of your pip installation to your PATH variable, you can use the Control Panel or the
setx command. For example:
setx PATH "%PATH%;C:\Python34\Scripts"
Note: According to the official documentation, “[v]ariables set with setx variables are available in future command windows only, not in the current command window”. In particular, you will need to start a new cmd.exe instance after entering the above command in order to utilize the new environment variable.
Thanks to Scott Bartell for pointing this out.