Susy 3.0.8

The Susy3 Philosophy

We no longer recommend using Susy as a primary layout solution.

With the advent of flexbox and the CSS Grid module, there are fewer and fewer reasons to use a grid library like Susy, and that’s wonderful! Grid libraries were always a temporary fix, waiting for the browser to take over. Still, not everyone can play with the latest specs, and there will always be edge-cases that require manual grid-math.

Susy3 is trimmed down to the most basic features: a lightweight library of functions that can be used along with float, flexbox, or any other CSS. Susy can be used for on-the-fly grid-math, or used to generate a class-based system – so that your grids are built to spec for the requirements of your team and application.

Not For Everyone

Much of the power and flexibility in Susy is now available directly in the browser with additional benefits and lower overhead.

CSS Grids

The CSS Grid module is relatively new, but has gained browser-support quickly – and there is no third-party tool available with the same power and simplicity it provides. Rachel Andrew and Jen Simmons have compiled a comprehensive set of articles, examples, and even copy-paste templates (with fallbacks built in) on their site.


Flexbox also provides intrinsic sizing and relationships, with near-complete support in modern browsers which can help make strict/explicit grids obsolete.


If you need a grid system that works with legacy browsers, I recommend an approach similar to OOCSS. While their code is out of date, the approach is worth adopting to modern practices:

  • Remove gutters (or use padding for gutters) to dramatically simplify the grid math.
  • Use simple fractions to create a robust nested grid.
  • Optionally create class-names as needed.

Those techniques can be used with floats, flexbox, display-tables, and more. In Sass it might looks something like this:

.span1of2 {
  width: percentage(1/2);

.span3of12 {
  width: percentage(3/12);

This is the same technique used by previous versions of Susy when you set gutter-position to inside or inside-static. In order to create a class-based system in Sass, you can run a loop like this one:

$columns: 12;

[class^='span'] {
  float: left;

@for $i from 1 through $columns {
  .span#{$i}of#{$columns} {
    width: percentage($i / $columns);

Without ever loading a third-party tool, you can design your own grid system in a few lines of code.

Susy as a Fallback

Susy3 works similarly to the percentage() technique, but provides support for margin-gutters and (simple) mixed-unit grids:

.span1of2 {
  width: span(1 of 2);
  margin-right: gutter(of 2);

.span3of12 {
  width: span(3 of 12);
  margin: 0 (gutter() / 2);

When the math gets complicated, Susy can be there to step in – but there is no need for Susy if you can keep the math simple.

No Mixins

The biggest change in Susy3 is that we’ve removed all the mixins. On initial upgrade, most projects will run into errors with missing mixins – container, span, or otherwise. While mixins can provide a nice shortcut for common use-cases, they also make the actual CSS more opaque, and quickly become out-of-date – discouraging incremental improvements to your application.

In a world with growing browser support for any number of powerful CSS layout techniques, it would be neglegent of us to push everyone into a single one-size-fits-all solution. There are other frameworks that provide that service, but Susy was never intended to be one of them.


See our full list of Susy News & Tutorials for more details.