Sass mixins I use for responsive design to calculate width percents quickly

responsiveMixins.sass

//responsive Design mixins, it's recommended that if you need a different 
//pageWidth than the default of 960px that proxy functions be made to change the default ex:
// =rwidth1($width)
//		+rwidth($width, 800px)
//
//this makes it faster to use

//calculates a percentage based width based on the pageWidth constant and the given width
=rwidth($width,$pageWidth : 960px)
	/*! #{$width}/#{$pageWidth}*/
	width: percentage($width/$pageWidth) 
	
=rmargin($top,$right,$bottom,$left, $pageWidth : 960px)
	@if $top == 0
		$top: 0px
	
	@if $right == 0
		$right: 0px
		
	@if $bottom == 0
		$bottom: 0px
		
	@if $left == 0
		$left: 0px
		
	/*! #{$top}, #{$right}/#{$pageWidth}, #{$bottom}, #{$left}/#{$pageWidth} */
	
	margin: $top percentage($right/$pageWidth) $bottom percentage($left/$pageWidth) 

=rpadding($top,$right,$bottom,$left, $pageWidth : 960px)
	@if $top == 0
		$top: 0px
	
	@if $right == 0
		$right: 0px
		
	@if $bottom == 0
		$bottom: 0px
		
	@if $left == 0
		$left: 0px
		
	/*! #{$top}, #{$right}/#{$pageWidth}, #{$bottom}, #{$left}/#{$pageWidth} */
	
	padding: $top percentage($right/$pageWidth) $bottom percentage($left/$pageWidth)