Each column in a layout has a $column->width() method which will return the width defined in the blueprint. (i.e. 1/2) but for many grid systems you need to know how many columns the current column should span in the grid. This can be done with the $column->span() method. The method calculates with a 12-column grid by default. So for example, if your column width is 1/2 the span method would return a value of 6. If you are working with a different kind of grid system you can pass the number of columns like this: $column->span(6):
In some cases, you might even want to controll the way blocks within layouts are rendered. $column->blocks() will return a blocks collection that you can work with and create another nested foreach loop.