The Genesis stylesheet has a great feature called Column Classes. This allows you to easily break a page’s content into multiple columns.
But if you’re like me, you’ll receive design files from the client’s designer and she’s using a grid of her own. You should then update the CSS of the column classes to match this grid, but that can be a big hassle (and a lot of math).
I’ve done the hard work for you! Simply drop the page’s width and gutter (space between columns) in here, and it will create the column classes for you. You can then copy/paste it into your own theme.