Generated by SassMeister.com.

SassMeister-input-HTML.html

<h1>Hello World</h1>

SassMeister-input.scss

// ----
// Sass (v3.4.12)
// Compass (v1.0.3)
// ----

// This could be one of your mq breakpoint variables
$wide-screen : "(min-width: 1025px)"; 

// Function
@function get-vw($target) {
  // 1 vw is equal to 1% of the viewport width
  $vw-context: (1000*.01) * 1px;
  @return ($target/$vw-context) * 1vw;
}

// Mixin
@mixin vw($f) {
  font-size: get-vw($f);
  // Prevent font-size from getting too big
  @media #{$wide-screen} {
    font-size: $f;
  }
}

// Using it
h1 {
 @include vw(72px);
}

// If the width of the viewport is 1025px or wider, 
// the font size will remain at 72px. 
// Otherwise, the value will adjust as 7.2vw

SassMeister-output.css

h1 {
  font-size: 7.2vw;
}
@media (min-width: 1025px) {
  h1 {
    font-size: 72px;
  }
}

SassMeister-rendered.html

<h1>Hello World</h1>