officialWebsite/node_modules/@fortawesome/fontawesome-free/scss/_sizing.scss

// sizing icons
// -------------------------
@use 'variables' as v;
@use 'mixins' as m;

// literal magnification scale
@for $i from 1 through 10 {
  .#{v.$css-prefix}-#{$i}x {
    font-size: $i * 1em;
  }
}

// step-based scale (with alignment)
@each $size, $value in v.$sizes {
  .#{v.$css-prefix}-#{$size} {
     @include m.fa-size($value);
  }
}