Sass Variable in CSS calc() function

To use $variables inside your calc() of the height property:

HTML:

<div></div>

SCSS:

$a: 4em;

div {
  height: calc(#{$a} + 7px);
  background: #e53b2c;
}

Interpolate:

body
    height: calc(100% - #{$body_padding})

For this case, border-box would also suffice:

body
    box-sizing: border-box
    height: 100%
    padding-top: $body_padding

Even though its not directly related. But I found that the CALC code won't work if you do not put spaces properly.

So this did not work for me calc(#{$a}+7px)

But this worked calc(#{$a} + 7px)

Took me sometime to figure this out.

I have tried this then i fixed my issue. It will calculate all media-breakpoint automatically by given rate (base-size/rate-size)

$base-size: 16;
$rate-size-xl: 24;

    // set default size for all cases;
    :root {
      --size: #{$base-size};
    }

    // if it's smaller then LG it will set size rate to 16/16;
    // example: if size set to 14px, it will be 14px * 16 / 16 = 14px
    @include media-breakpoint-down(lg) {
      :root {
        --size: #{$base-size};
      }
    }

    // if it is bigger then XL it will set size rate to 24/16;
    // example: if size set to 14px, it will be 14px * 24 / 16 = 21px
    @include media-breakpoint-up(xl) {
      :root {
        --size: #{$rate-size-xl};
      }
    }

@function size($px) {
   @return calc(#{$px} / $base-size * var(--size));
}

div {
  font-size: size(14px);
  width: size(150px);
}