Modified version of the `spacing-classes` pattern from Stitch. Allows you to specify additional units for output.

spacing-class.css.scss

// Generate inline class names for your elements
//
// <div class="actions inset-vert-small-large">
//    <button type="submit">Totes click me!</button>
// </div>
//
// Padding
// ---------------
// pad-{item}           :  pad-small (padding: 10px)
// pad-vert-{item}-{item + 1}     :  pad-vert-small-large (padding: 10px 0 40px 0)
// pad-horz-{item}-{item + 1}     :  pad-horz-small-large (padding: 0 10px 0 40px)
//
// Margin
// ---------------
// inset-{item}           :  inset-small (margin: 10px)
// inset-vert-{item}-{item + 1}   :  inset-vert-small-large (margin: 10px 0 40px 0)
// inset-horz-{item}-{item + 1}   :  inset-horz-small-large (margin: 0 10px 0 40px)
//
// Offset margin
// ---------------
// offset-{item}          :  offset-small (margin: -10px)
// offset-vert-{item}-{item + 1}  :  offset-vert-small-large (margin: -10px 0 -40px 0)
// offset-horz-{item}-{item + 1}  :  offset-horz-small-large (margin: 0 -10px 0 -40px)

@mixin spacing-classes($base: 10, $list: small normal medium large, $units: px rem) {
  @for $i from 1 through length($list) {

    .pad-#{nth(unquote($list), $i)} {
      @for $u from 1 through length($units) {
        $unit: nth(unquote($units), $u);
        $divisor: if($unit == rem, 10, 1);
        padding: ($base * $i / $divisor)#{$unit};
      }
    }

    .inset-#{nth(unquote($list), $i)} {
      @for $u from 1 through length($units) {
        $unit: nth(unquote($units), $u);
        $divisor: if($unit == rem, 10, 1);
        margin: ($base * $i / $divisor)#{$unit};
      }
    }

    .offset-#{nth(unquote($list), $i)} {
      @for $u from 1 through length($units) {
        $unit: nth(unquote($units), $u);
        $divisor: if($unit == rem, 10, 1);
        margin: (-($base * $i / $divisor))#{$unit};
      }
    }

    .pad-top-#{nth(unquote($list), $i)} {
      @for $u from 1 through length($units) {
        $unit: nth(unquote($units), $u);
        $divisor: if($unit == rem, 10, 1);
        padding-top: ($base * $i / $divisor)#{$unit};
      }
    }

    .pad-right-#{nth(unquote($list), $i)} {
      @for $u from 1 through length($units) {
        $unit: nth(unquote($units), $u);
        $divisor: if($unit == rem, 10, 1);
        padding-right: ($base * $i / $divisor)#{$unit};
      }
    }

    .pad-bottom-#{nth(unquote($list), $i)} {
      @for $u from 1 through length($units) {
        $unit: nth(unquote($units), $u);
        $divisor: if($unit == rem, 10, 1);
        padding-bottom: ($base * $i / $divisor)#{$unit};
      }
    }

    .pad-left-#{nth(unquote($list), $i)} {
      @for $u from 1 through length($units) {
        $unit: nth(unquote($units), $u);
        $divisor: if($unit == rem, 10, 1);
        padding-left: ($base * $i / $divisor)#{$unit};
      }
    }

    .inset-top-#{nth(unquote($list), $i)} {
      @for $u from 1 through length($units) {
        $unit: nth(unquote($units), $u);
        $divisor: if($unit == rem, 10, 1);
        margin-top: ($base * $i / $divisor)#{$unit};
      }
    }

    .inset-right-#{nth(unquote($list), $i)} {
      @for $u from 1 through length($units) {
        $unit: nth(unquote($units), $u);
        $divisor: if($unit == rem, 10, 1);
        margin-right: ($base * $i / $divisor)#{$unit};
      }
    }

    .inset-bottom-#{nth(unquote($list), $i)} {
      @for $u from 1 through length($units) {
        $unit: nth(unquote($units), $u);
        $divisor: if($unit == rem, 10, 1);
        margin-bottom: ($base * $i / $divisor)#{$unit};
      }
    }

    .inset-left-#{nth(unquote($list), $i)} {
      @for $u from 1 through length($units) {
        $unit: nth(unquote($units), $u);
        $divisor: if($unit == rem, 10, 1);
        margin-left: ($base * $i / $divisor)#{$unit};
      }
    }

    .outset-top-#{nth(unquote($list), $i)} {
      @for $u from 1 through length($units) {
        $unit: nth(unquote($units), $u);
        $divisor: if($unit == rem, 10, 1);
        margin-top: (-($base * $i / $divisor))#{$unit};
      }
    }

    .outset-right-#{nth(unquote($list), $i)} {
      @for $u from 1 through length($units) {
        $unit: nth(unquote($units), $u);
        $divisor: if($unit == rem, 10, 1);
        margin-right: (-($base * $i / $divisor))#{$unit};
      }
    }

    .outset-bottom-#{nth(unquote($list), $i)} {
      @for $u from 1 through length($units) {
        $unit: nth(unquote($units), $u);
        $divisor: if($unit == rem, 10, 1);
        margin-bottom: (-($base * $i / $divisor))#{$unit};
      }
    }

    .outset-left-#{nth(unquote($list), $i)} {
      @for $u from 1 through length($units) {
        $unit: nth(unquote($units), $u);
        $divisor: if($unit == rem, 10, 1);
        margin-left: (-($base * $i / $divisor))#{$unit};
      }
    }

    .inset-#{nth(unquote($list), $i)} {
      @for $u from 1 through length($units) {
        $unit: nth(unquote($units), $u);
        $divisor: if($unit == rem, 10, 1);
        margin: ($base * $i / $divisor)#{$unit};
      }
    }

    .offset-#{nth(unquote($list), $i)} {
      @for $u from 1 through length($units) {
        $unit: nth(unquote($units), $u);
        $divisor: if($unit == rem, 10, 1);
        margin: (-($base * $i / $divisor))#{$unit};
      }
    }

    .pad-vert-#{nth(unquote($list), $i)} {
      @for $u from 1 through length($units) {
        $unit: nth(unquote($units), $u);
        $divisor: if($unit == rem, 10, 1);
        padding-top: ($base * $i / $divisor)#{$unit};
        padding-bottom: ($base * $i / $divisor)#{$unit};
      }
    }

    .pad-horz-#{nth(unquote($list), $i)} {
      @for $u from 1 through length($units) {
        $unit: nth(unquote($units), $u);
        $divisor: if($unit == rem, 10, 1);
        padding-right: ($base * $i / $divisor)#{$unit};
        padding-left: ($base * $i / $divisor)#{$unit};
      }
    }

    .inset-vert-#{nth(unquote($list), $i)} {
      @for $u from 1 through length($units) {
        $unit: nth(unquote($units), $u);
        $divisor: if($unit == rem, 10, 1);
        margin-top: ($base * $i / $divisor)#{$unit};
        margin-bottom: ($base * $i / $divisor)#{$unit};
      }
    }

    .inset-horz-#{nth(unquote($list), $i)} {
      @for $u from 1 through length($units) {
        $unit: nth(unquote($units), $u);
        $divisor: if($unit == rem, 10, 1);
        margin-right: ($base * $i / $divisor)#{$unit};
        margin-left: ($base * $i / $divisor)#{$unit};
      }
    }

    .offset-vert-#{nth(unquote($list), $i)} {
      @for $u from 1 through length($units) {
        $unit: nth(unquote($units), $u);
        $divisor: if($unit == rem, 10, 1);
        margin-top: (-($base * $i / $divisor))#{$unit};
        margin-bottom: (-($base * $i / $divisor))#{$unit};
      }
    }

    .offset-horz-#{nth(unquote($list), $i)} {
      @for $u from 1 through length($units) {
        $unit: nth(unquote($units), $u);
        $divisor: if($unit == rem, 10, 1);
        margin-left: (-($base * $i / $divisor))#{$unit};
        margin-right: (-($base * $i / $divisor))#{$unit};
      }
    }

    @for $j from 1 through length($list) {

      @if ($i != $j) {

        .pad-vert-#{nth(unquote($list), $i)}-#{nth(unquote($list), ($j))} {
          @for $u from 1 through length($units) {
        $unit: nth(unquote($units), $u);
        $divisor: if($unit == rem, 10, 1);
            padding-top: ($base * $i / $divisor)#{$unit};
            padding-bottom: ($base * $j)#{$unit};
          }
        }

        .pad-horz-#{nth(unquote($list), $i)}-#{nth(unquote($list), ($j))} {
          @for $u from 1 through length($units) {
        $unit: nth(unquote($units), $u);
        $divisor: if($unit == rem, 10, 1);
            padding-right: ($base * $i / $divisor)#{$unit};
            padding-left: ($base * $j)#{$unit};
          }
        }

        .inset-vert-#{nth(unquote($list), $i)}-#{nth(unquote($list), ($j))} {
          @for $u from 1 through length($units) {
        $unit: nth(unquote($units), $u);
        $divisor: if($unit == rem, 10, 1);
            margin-top: ($base * $i / $divisor)#{$unit};
            margin-bottom: ($base * $j)#{$unit};
          }
        }

        .inset-horz-#{nth(unquote($list), $i)}-#{nth(unquote($list), ($j))} {
          @for $u from 1 through length($units) {
        $unit: nth(unquote($units), $u);
        $divisor: if($unit == rem, 10, 1);
            margin-right: ($base * $i / $divisor)#{$unit};
            margin-left: ($base * $j)#{$unit};
          }
        }

        .offset-vert-#{nth(unquote($list), $i)}-#{nth(unquote($list), ($j))} {
          @for $u from 1 through length($units) {
        $unit: nth(unquote($units), $u);
        $divisor: if($unit == rem, 10, 1);
            margin-top: (-($base * $i / $divisor))#{$unit};
            margin-bottom: (-($base * $j))#{$unit};
          }
        }

        .offset-horz-#{nth(unquote($list), $i)}-#{nth(unquote($list), ($j))} {
          @for $u from 1 through length($units) {
        $unit: nth(unquote($units), $u);
        $divisor: if($unit == rem, 10, 1);
            margin-right: (-($base * $i / $divisor))#{$unit};
            margin-left: (-($base * $j))#{$unit};
          }
        }
      }
    }
  }
}