Fatal error: Unable to find local grunt

I think you don't have a grunt.js file in your project directory. Use grunt:init, which gives you options such as jQuery, node,commonjs. Select what you want, then proceed. This really works. For more information you can visit this.

Do this:

 1. npm install -g grunt
 2. grunt:init  ( you will get following options ):
      jquery: A jQuery plugin
      node: A Node module
      commonjs: A CommonJS module
      gruntplugin: A Grunt plugin
      gruntfile: A Gruntfile (grunt.js)
 3 .grunt init:jquery (if you want to create a jQuery related project.).

It should work.

Solution for v1.4:

1. npm install -g grunt-cli
2. npm init
   fill all details and it will create a package.json file.
3. npm install grunt (for grunt dependencies.)

Edit : Updated solution for new versions:

npm install grunt --save-dev