---
title: "@while"
---

The `@while` rule, written `@while <expression> { ... }`, evaluates its block if
its [expression][] returns `true`. Then, if its expression still returns `true`,
it evaluates its block again. This continues until the expression finally
returns `false`.

[expression]: ../../syntax/structure#expressions

<% example do %>
  /// Divides `$value` by `$ratio` until it's below `$base`.
  @function scale-below($value, $base, $ratio: 1.618) {
    @while $value > $base {
      $value: $value / $ratio;
    }
    @return $value;
  }

  $normal-font-size: 16px;
  sup {
    font-size: scale-below(20px, 16px);
  }
  ===
  /// Divides `$value` by `$ratio` until it's below `$base`.
  @function scale-below($value, $base, $ratio: 1.618)
    @while $value > $base
      $value: $value / $ratio
    @return $value;



  $normal-font-size: 16px
  sup
    font-size: scale-below(20px, 16px)
<% end %>

<% heads_up do %>
  Although `@while` is necessary for a few particularly complex stylesheets, you're
  usually better of using either [`@each`][] or [`@for`][] if either of them will
  work. They're clearer for the reader, and often faster to compile as well.

  [`@each`]: each
  [`@for`]: for
<% end %>

<%= partial 'documentation/snippets/truthiness-and-falsiness' %>