Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.2.10)
// Compass (v0.13.alpha.4)
// ----

$basePixelSize:12;

@function calcFontSize($value:100, $_unit:$unit, $base:$basePixelSize) {
  @if $_unit == 'px' {
    @return ($base * $value / 100)#{$_unit};
  }

  @if $_unit == 'rem' {
    @return ($value / 100)#{$_unit};
  }

  @if $_unit == '%' {
    @return $value#{$_unit};
  }
}

@mixin fontSize($_size:null, $_unit:$unit, $_fbUnit:$fbUnit) {
  font-size: calcFontSize($_size, $_fbUnit); //percent (%) equivalent to 11px
  font-size: calcFontSize($_size, $_unit); //rem equivalent to 11px
}

.foo{
    @include fontSize(91.6667,'rem','px');
}

SassMeister-output.css

.foo {
  font-size: 11.0px;
  font-size: 0.91667rem;
}