About Susy

Guides are not rules and should not be followed blindly. Use your head and think.

Important: this guide is made for Susy 2. For information about Susy 3, check out Susy 3 Docs.

Susy is a sass library that handles grid layouting and the math behind it, and contains some utilities. It has no inherent styling choices, as it is meant to be used only for the grid. Understanding the use of Susy mostly revolves about knowing its utilities and its configuration, so the guide will first focus on that.


Before going through this guide, some knowledge of sass is needed. For that, check the SASS reference.

The guide is effectively split into two parts: Susy configuration and the actual guide. A more in-depth configuration explanation can be found in the documentation. If you are familiar with Susy, skip to the guide section.


First, we'll go through the configuration. The usage of some of this might not be immediately apparent but will be explained in the guide section.

$susy: (
  flow: ltr,
  last-flow: to,
  math: fluid,
  column-width: false,
  output: float,
  container: auto,
  container-position: center,
  columns: 4,
  gutters: 0.25,
  gutter-position: after,
  global-box-sizing: content-box,
  debug: (
    image: hide,
    color: rgba(128, 128, 255, 0.25),
    output: background,
    toggle: top right,
  use-custom: (
    background-image: true,
    background-options: false,
    box-sizing: true,
    clearfix: false,
    rem: true,

Flow and last flow

flow is used to direct the flow of the columns. This is almost always going to be ltr (left to right) with the other option being rtl (right to left)

last-flow tells Susy where to float the last column. from will float to the left (assuming ltr flow) while to will float to the right. (to is preferable). This isn't something you should touch unless you're sure that you need it.

Math and column width

math is used to decide how and in which units to calculate column and gutter widths.

fluid math will output everything as percentages such as to be relative to the parent container. This is what you will use the most.
static math is used to output depending on the value in column-width (which has to be set for static math to be useful).

column-width can be set to either false or null, and this is the default, as for fluid widths it only sets the outer maximum width or a static unit such as 200px or 10em.


output handles the way columns' positions are generated. float is the default and uses float to position elements, while isolate uses a negative margin trick. Use float as it is slightly more performant and much easier to spot errors and debug with. isolate is only useful when facing sub-pixel rounding errors, which it can avoid.

Container and container position

container is used to set the max-width of the element with the applied container mixin. This can be either a relative or a static unit. If using static layouts, this is best left at auto in order to avoid sub-pixel rounding errors.

Container position sets where the columns will be positioned relative to the container. Center is usually preferred.


columns determine the number of columns in the current layout. This is something you will probably use the most, as it is very versatile for creating any grid layout you need.

Gutters and gutter position

gutters is the width of the gutter between columns, and the size is based on the column width. Therefore, .25 means one quarter of the column width of one unit column.

gutter-position tells Susy where to put gutters. In case of after, gutters will be applied as margins on the right of the column, meaning that the last column in the container should have no right margin. This is solved in the span mixin whose usage will be explained in the guide section.

The possible values are:

Border box sizing

global-box-sizing tells Susy the global default sizing, so it can calculate column and gutters correctly.

This does NOT set box-sizing globally.

There is a mixin for that which will be explained in the guide section.


There are also debug and custom options, which are not important for the purpose for this guide, so you can read about those in the documentation.

Susy documentation
For anything that is unclear, check the documentation for details.