Keeping Gutenberg’s Core Columns Block Aligned to the Grid.

The WordPress Gutenberg editor comes with a load of power to create custom layouts. However, as Spiderman said, with great power comes great responsiblity… so how do we reduce the risk of our meticulously designed site being messed up by an editor who is not design-savvy?

In this post we are going to focus on one aspect of this, the core column block. Our designs are normally based on a 12-column grid, however the column block allows the editor to enter any percentage width they like for each column. This means they can create columns which are 5% or even 98% wide, ignoring our grid completely. What a mess they could make!

In the Lean theme we came up with a simple solution for this – the columns are automatically snapped to the nearest width allowed on a 12-column grid (ie a multiple of 8.333%). Here’s how we did it:

First we hooked into the render_block filter and called functions we’ll use to add classes to all core/columns blocks (the wrapper block for a set of columns) and all core/column blocks (an individual column).

You’ll note we used this WordPress PHP hook instead of a hook from the JavaScript API. We felt this is better for maintainability, as the hook updates the block at render time only. The JavaScript hook updates the block data which is saved to the database, this means any further changes to the saved HTML could invalidate existing blocks meaning they have to be fixed or even re-created.

We only need to add two classes to the core/columns wrapper: md:flex -mx-1. Using TailWindCSS these apply the necessary CSS properties to set up a flex grid within the container (see the TailWind flex grid documentation):

For now we’re using strpos and substr_replace functions to manipulate the HTML string. We could of course use a PHP DOM parser library to simplify this further.

Now the real magic happens on the individual column blocks. On mobile we want them to be full width so the columns stack, and then switch the to column layout from the medium breakpoint upwards.

First we get the % width set in the editor from the $block properties. This can be null if no widths are set at all – in this case we assume the user wants the columns to auto-size, so we don’t add any width class at all and let flex auto-size them.

Then, assuming a width is set, we round it to the nearest factor of 12 / 100 to snap it to the closest width available on a 12 columns grid. In TailWind we use the w-1/12, w-2/12, … w-11/12 classes to achieve this.


This is definitely a quick fix, a better solution would be to customise the core/column block width controls (or replace the block with a completely custom one) so the user has to select some sort of “columns to span” amount. This is quite a bit more complex, as it involves building the logic to ensure the total is always 12, as well as some other probably gotchas.

I hope this was useful or at least a little interesting. You can contact me at or via the comments section if you have any questions, comments or suggestions. Also check out these resources:

  • My Lightening Talk on Building a Gutenberg Enabled Theme for Non-designers.
  • The full gist of this code example.
  • A working example in the blocks section of the Lean Theme.

Let’s launch something!