Mixins

mixins.scss

@mixin bp($point) {

  @if $point == print {
		@media only print { @content; }
	}

}

@mixin em_width($px) { width: #{$px / 16}em; }
@mixin em_maxwidth($px) { max-width: #{$px / 16}em; }
@mixin em_margin($top:0,$right:0,$bot:0,$left:0) { margin: #{$top / 16}em #{$right / 16}em #{$bot / 16}em #{$left / 16}em }
@mixin em_padding($top:0,$right:0,$bot:0,$left:0) { padding: #{$top / 16}em #{$right / 16}em #{$bot / 16}em #{$left / 16}em }
@mixin em_fontsize($px) { font-size: #{$px / 16}em; }

// My setup for sprites
@import "../img/*.png";
@include all-img-sprites;

$sprites: logo_header cats;

@mixin sprite-dimensions($name) {
  width: img-sprite-width($name);
	height: img-sprite-height($name);
}

.sprite {

	display: inline-block;	
	background-color: transparent;

}

@each $sprite in $sprites {
	.#{$sprite} {
		@include img-sprite($sprite); 
		@include sprite-dimensions($sprite);
	}
}

I forked and added min and max height and min width.