So, you've setup 4 columns, and a default page limit of 16 in your configuration somewhere but somewhere, you'd like to run a 3 column count with 12 products per page? Here's how you do it.

  1. Click your category in Magento Admin
  2. Switch to the Custom Design Tab
  3. Enter the folowing XML in the Custom Layout Update


<reference name="product_list">
 <action method="setColumnCount"><columns>3</columns></action>
 </reference> <reference name="product_list_toolbar">
     <action method="addPagerLimit"><mode>grid</mode><limit>12</limit></action>