How to make a responsive google map from the code
I use in css
Check this for a solution: http://jsfiddle.net/panchroma/5AEEV/
I can't take the credit for the code though, it comes from quick and easy way to make google maps iframe embed responsive.
Good luck!
CSS
#map_canvas{
width:50%;
height:300px !important;
}
HTML
Google Maps JavaScript API v3 Example: Map Simple