How can get length on checked checkbox array with jquery?

I want to have jquery get length of checkbox array checked as:

<li><input name="skills['11111']" class="skills" value="1" type="checkbox" /></li> <li><input name="skills['22222']" class="skills" value="2" type="checkbox" /></li> <li><input name="skills['33333']" class="skills" value="3" type="checkbox" /></li> <li><input name="skills['44444444']" class="skills" value="4" type="checkbox" /></li>

So, it will response length = 4 Any idea?