danielrayjones/_assets/css/responsive_sizes.scss

@each $prop, $abbrev in (width: w, height: h) {
  @each $bpname,$bpsize in $grid-breakpoints {
    @media (min-width: $bpsize) {
      @each $size, $length in $sizes {
        .#{$abbrev}-#{$bpname}-#{$size} {
          #{$prop}: $length;
        }
        .m#{$abbrev}-#{$bpname}-#{$size} {
            max-#{$prop}: $length;
        }
      }
    }
  }
}