Equal height rows in CSS Grid Layout

Short Answer

If the goal is to create a grid with equal height rows, where the tallest cell in the grid sets the height for all rows, here's a quick and simple solution:

  • Set the container to grid-auto-rows: 1fr

How it works

Grid Layout provides a unit for establishing flexible lengths in a grid container. This is the fr unit. It is designed to distribute free space in the container and is somewhat analogous to the flex-grow property in flexbox.

If you set all rows in a grid container to 1fr, let's say like this:

grid-auto-rows: 1fr;

... then all rows will be equal height.

It doesn't really make sense off-the-bat because fr is supposed to distribute free space. And if several rows have content with different heights, then when the space is distributed, some rows would be proportionally smaller and taller.

Except, buried deep in the grid spec is this little nugget:

7.2.3. Flexible Lengths: the fr unit

...

When the available space is infinite (which happens when the grid container’s width or height is indefinite), flex-sized (fr) grid tracks are sized to their contents while retaining their respective proportions.

The used size of each flex-sized grid track is computed by determining the max-content size of each flex-sized grid track and dividing that size by the respective flex factor to determine a “hypothetical 1fr size”.

The maximum of those is used as the resolved 1fr length (the flex fraction), which is then multiplied by each grid track’s flex factor to determine its final size.

So, if I'm reading this correctly, when dealing with a dynamically-sized grid (e.g., the height is indefinite), grid tracks (rows, in this case) are sized to their contents.

The height of each row is determined by the tallest (max-content) grid item.

The maximum height of those rows becomes the length of 1fr.

That's how 1fr creates equal height rows in a grid container.


Why flexbox isn't an option

As noted in the question, equal height rows are not possible with flexbox.

Flex items can be equal height on the same row, but not across multiple rows.

This behavior is defined in the flexbox spec:

6. Flex Lines

In a multi-line flex container, the cross size of each line is the minimum size necessary to contain the flex items on the line.

In other words, when there are multiple lines in a row-based flex container, the height of each line (the "cross size") is the minimum height necessary to contain the flex items on the line.


The short answer is that setting grid-auto-rows: 1fr; on the grid container solves what was asked.

* {
  box-sizing: border-box;
}

.container {
  max-width: 800px;
  margin: 0 auto;
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  grid-auto-rows: 1fr;
  grid-column-gap: 30px;
  grid-row-gap: 30px;
}

.description {
  background: blue;
  grid-column: 1 / span 4;
}

.col {
  background: red;
}
<div class="container">
  <div class="description">
    Lorem ipsum in ut amet aute eu nulla labore do exercitation magna aliquip commodo dolore aute fugiat labore dolore ad culpa dolore pariatur qui in sed est magna cillum nisi ex deserunt sit incididunt aliquip adipisicing in officia.
  </div>
  <div class="col">
    Lorem ipsum dolor sit amet, consectetur adipisicing elit. Labore quam deserunt, reprehenderit! Saepe nesciunt laborum, sapiente autem laboriosam quaerat officia dolore similique enim, dolor placeat magni neque iure maiores. Dicta. Lorem ipsum dolor sit
    amet, consectetur adipisicing elit. Labore quam deserunt, reprehenderit! Saepe nesciunt laborum, sapiente autem laboriosam quaerat officia dolore similique enim, dolor placeat magni neque iure maiores. Dicta. Lorem ipsum dolor sit amet, consectetur
    adipisicing elit. Labore quam deserunt, reprehenderit! Saepe nesciunt laborum, sapiente autem laboriosam quaerat officia dolore similique enim, dolor placeat magni neque iure maiores. Dicta.
  </div>
  <div class="col">
    Lorem ipsum dolor sit amet, consectetur adipisicing elit. Labore quam deserunt, reprehenderit! Saepe nesciunt laborum, sapiente autem laboriosam quaerat officia dolore similique enim, dolor placeat magni neque iure maiores. Dicta.
  </div>
  <div class="col">
  </div>
  <div class="col">
  </div>
  <div class="col">
  </div>
  <div class="col">
  </div>
  <div class="col">
  </div>
  <div class="col">
    Lorem ipsum in ut amet aute eu nulla labore do exercitation magna aliquip commodo dolore aute fugiat labore dolore ad culpa dolore pariatur qui in sed est magna cillum nisi ex deserunt sit incididunt aliquip adipisicing in officia.
  </div>
  <div class="col">
  </div>
  <div class="col">
  </div>
  <div class="description">
    Lorem ipsum in ut amet aute eu nulla labore do exercitation magna aliquip commodo dolore aute fugiat labore dolore ad culpa dolore pariatur qui in sed est magna cillum nisi ex deserunt sit incididunt aliquip adipisicing in officia.
  </div>
  <div class="col">
  </div>
  <div class="col">
  </div>
  <div class="col">
  </div>
  <div class="col">
  </div>
  <div class="col">
    Lorem ipsum dolor sit amet, consectetur adipisicing elit. Labore quam deserunt, reprehenderit! Saepe nesciunt laborum, sapiente autem laboriosam quaerat officia dolore similique enim, dolor placeat magni neque iure maiores. Dicta.
  </div>
  <div class="col">
  </div>
  <div class="col">
    Lorem ipsum dolor sit amet, consectetur adipisicing elit. Labore quam deserunt, reprehenderit! Saepe nesciunt laborum, sapiente autem laboriosam quaerat officia dolore similique enim, dolor placeat magni neque iure maiores. Dicta.
  </div>
  <div class="col">
  </div>
  <div class="col">
  </div>
  <div class="col">
  </div>
  <div class="description">
    Lorem ipsum in ut amet aute eu nulla labore do exercitation magna aliquip commodo dolore aute fugiat labore dolore ad culpa dolore pariatur qui in sed est magna cillum nisi ex deserunt sit incididunt aliquip adipisicing in officia.
  </div>
  <div class="col">
  </div>
  <div class="col">
    Lorem ipsum in ut amet aute eu nulla labore do exercitation magna aliquip commodo dolore aute fugiat labore dolore ad culpa dolore pariatur qui in sed est magna cillum nisi ex deserunt sit incididunt aliquip adipisicing in officia.
  </div>
  <div class="col">
  </div>
  <div class="col">
  </div>
  <div class="col">
  </div>
  <div class="col">
  </div>
  <div class="col">
  </div>
  <div class="col">
  </div>
  <div class="col">
  </div>
  <div class="col">
  </div>
  <div class="description">
    Lorem ipsum in ut amet aute eu nulla labore do exercitation magna aliquip commodo dolore aute fugiat labore dolore ad culpa dolore pariatur qui in sed est magna cillum nisi ex deserunt sit incididunt aliquip adipisicing in officia.
  </div>
  <div class="col">
  </div>
  <div class="col">
  </div>
  <div class="col">
  </div>
  <div class="col">
  </div>
  <div class="col">
  </div>
  <div class="col">
  </div>
  <div class="col">
  </div>
  <div class="col">
    Lorem ipsum in ut amet aute eu nulla labore do exercitation magna aliquip commodo dolore aute fugiat labore dolore ad culpa dolore pariatur qui in sed est magna cillum nisi ex deserunt sit incididunt aliquip adipisicing in officia.
  </div>
  <div class="col">
  </div>
  <div class="col">
  </div>
</div>

View on CodePen