Fortuna theme has the option to easily hide the sidebar to display 4 products on each row on category page. But it’s easy to display 4 products even if you have a sidebar enabled.

Just paste the following code in custom.css (if you are using a custom stylesheet) or in Custom CSS Code field in Fortuna Theme Options module.

#maincontent.span9 .grid-box {
  max-width: 25%; 
  min-width: 25%; 
  *width: 25%;
}
#maincontent.span9 .alpha4 {
  clear: left;
  margin-left: 0;
}
#maincontent.span9 .alpha3 {
  clear: none;
}
.span9 .grid-box .inner {
  border-left-color: #eee;
}
.grid-box.alpha .inner,
.span9 .alpha4 .inner, 
.span12 .alpha4 .inner {
  border-color:#fff;
}
.grid-box:hover .inner {
  border-color: #bbb;
}
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