Learn how to Use CSS aspect-ratio — SitePoint


There are occasions after we really want to take care of a particular ratio between the width and top of responsive components on an internet web page. This has been potential for a very long time through numerous CSS tips. The CSS aspect-ratio property is a sport changer, which means we will now specify the facet ratio of a component in a single line of code. Let’s have a look at how one can use aspect-ratio.

Desk of Contents
  1. Examples of The place Side Ratio is Essential
  2. Responsive YouTube Movies
  3. A Responsive Picture Gallery
  4. Sustaining Constant Avatar Sizes with aspect-ratio
  5. Helpful Issues to Learn about aspect-ratio
  6. Conclusion

Examples of The place Side Ratio is Essential

By its nature, the Net is a fluid medium, and it’s often higher to permit components on an internet web page to be as fluid and versatile as potential.

Nevertheless, there typically are causes to set limitations on the dimensions of components. For instance, we’d wish to preserve the width-to-height ratio of sure components — resembling responsive YouTube movies, gadgets in a picture gallery, or rounded avatars.

Let’s first have a look at three sensible makes use of of aspect-ratio, after which cowl some helpful issues to learn about the way it works.

Responsive YouTube Movies

If you happen to’ve ever embedded a YouTube video in an internet web page, you’ll know that the embed code comes as an <iframe> with fastened width and top. That’s okay, but it surely may very well be higher. Chances are high it’s not as huge as your container, which isn’t pretty. Worse, although, is that a few of it is likely to be misplaced offscreen on small viewports.

A YouTube embed narrower than the container on desktop and hidden partly offscreen on mobile

How a fixed-width YouTube embed seems on desktop (left) and cell (proper).

What we actually need is for the embedded video to fill a specific amount of area inside our design and be aware of totally different viewport widths. For simplicity, let’s say we wish it to fill 100% of the width of its container.

Let’s have a look at two methods to attain this — firstly, the outdated method, utilizing CSS trickery, after which the brand new method, with aspect-ratio.

Making a YouTube video responsive with the padding hack

YouTube supplies us the next embed code (simplified to save lots of area):

<iframe width="560" top="315" src=""></iframe>

A conventional trick for making our embed responsive is with the “padding hack”. The very first thing we now have to do is divide the width of the iframe by the peak, which can give us a ratio of width to top. YouTube movies are sometimes sized 560 by 315 pixels, so we have to divide 315 by 560, which supplies us .5625. Meaning the peak of our YouTube iframe is 56.25% of its width. This represents a ratio of 16:9, so hold that behind your thoughts.

We will now arrange our responsive YouTube embed in a couple of steps. Firstly, we wrap a component across the iframe, resembling a div:


We then set the div to place: relative and provides it a backside padding of 56.25%. The browser will calculate this share worth based mostly on the div’s width:

div {
  place: relative;
  padding-bottom: 56.25%;

The picture under reveals the div’s padding, highlighted in inexperienced through the browser’s developer instruments.

A green block with a ratio of 16:9 where our video will go

Word: should you don’t need the hassle of calculating the share of padding, you possibly can let the browser work it out for you. Merely insert the width and top of the iframe like so: padding-bottom: calc(315 / 560 * 100%).

Subsequent, we set the iframe to place: absolute and set its width and top to 100%:

iframe {
  place: absolute;
  width: 100%;
  top: 100%;

Now our YouTube embed can be responsive, filling 100% of the width of the container it doesn’t matter what the display screen dimension, whereas nonetheless sustaining its facet ratio, as proven under.

See the Pen
Responsive YouTube Video with the Padding Hack
by SitePoint (@SitePoint)
on CodePen.

Word: there are many different methods to attain the padding hack, resembling utilizing ::earlier than or ::after as a substitute of an additional div. They’re simple to search out on-line by trying to find “padding hack”.

Making a YouTube video responsive with aspect-ratio

We will make our YouTube video responsive with rather a lot much less code utilizing the aspect-ratio property. We not want the encircling div. We will simply set the next types on the iframe:

iframe {
  width: 100%;
  aspect-ratio: 16/9;

Ooh la la. Good. Test it out on CodePen.

See the Pen
Responsive YouTube Video with aspect-ratio
by SitePoint (@SitePoint)
on CodePen.

If you happen to don’t know the facet ratio of a component and don’t really feel like getting out your calculator, you might let the browser work it out for you, utilizing the width and top of the factor. Right here’s a variation of the CSS above:

iframe {
  --ratio: calc(315 / 560);
  width: 100%;
  aspect-ratio: 1/var(--ratio);

We all know the unique width and top of our iframe, so we plug them right into a customized property (--ratio), dividing top by width with the calc() operate. Then we use our customized property in a CSS variable as a part of aspect-ratio. Our facet ratio worth is now, successfully, 1/0.5625. So we will use floating-point numbers in our aspect-ratio values. (In fact, if you wish to apply this ratio to different components, then declare the customized property on a guardian larger up the tree, or on the :root factor itself.)

One more variation on this theme is simply to make use of calc() with out the customized property:

iframe {
  width: 100%;
  aspect-ratio: 1/calc(315 / 560);

That is nice if we’re solely utilizing this facet ratio worth on iframes.

Have a little bit of enjoyable and check out these variations within the CodePen demo above.

A Responsive Picture Gallery

Let’s say we wish to show a gallery of pictures in a sequence of versatile, sq. bins. We may use the padding hack to maintain the bins sq., however we will use aspect-ratio as a substitute. (The photographs are from my current climbing journey by the Unsplash web site.)

Right here’s our HTML:

  <li><img src="1.jpg" alt=""></li>
  <li><img src="2.jpg" alt=""></li><li><img src="11.jpg" alt=""></li>
  <li><img src="12.jpg" alt=""></li>

Right here’s the important thing CSS:

ul {
  show: grid;

li {
  aspect-ratio: 1/1;

img {
  object-fit: cowl;

The next CodePen demo reveals this code in motion.

See the Pen
Responsive Picture Gallery utilizing aspect-ratio
by SitePoint (@SitePoint)
on CodePen.

It’s a really fundamental demo. The grid columns are set to a width of 1fr, and the aspect-ratio: 1/1 ensures the cells stay completely sq., regardless of how huge or slim the browser. It is a actually useful option to management the peak of Grid rows.

The photographs all have random dimensions (none are sq.), in order that they’re made to suit inside their grid cell with object-fit: cowl. (Take a look at how one can use CSS object-fit if it’s new to you. The gallery can also be centered with Grid.)

Attempt taking part in round with the aspect-ratio property within the demo above. What occurs should you change the worth from 1/1 to 2/1, and so forth?

Sustaining Constant Avatar Sizes with aspect-ratio

In her lately launched e book Unleashing the Energy of CSS, Stephanie Eckles demonstrates using the aspect-ratio property to make sure constant avatar sizes. With aspect-ratio, together with the object-fit property, we will guarantee a constant avatar dimension whatever the unique picture ratio and with out distorting the picture.

Right here’s the important thing CSS:

img {
  aspect-ratio: 1; 
  object-fit: cowl;
  border-radius: 50%;
  width: 100%; 
  top: 100%;

The next Pen reveals this in motion.

See the Pen
Avatar listing with aspect-ratio and object-fit
by SitePoint (@SitePoint)
on CodePen.

As an experiment, strive commenting out the aspect-ratio: 1; line within the Pen above to see what occurs with out it! (You possibly can disable it by simply including a / on the entrance: /aspect-ratio: 1;.)

Helpful Issues to Learn about aspect-ratio

Each factor has a side ratio. If we don’t set a side ratio on a component, its facet ratio defaults to auto. If that factor is a changed factor resembling a picture, its facet ratio is set by its pure width and top. (That facet ratio can be preserved even when we set a unique width or top through CSS.)

Side ratio compares width (x) with top (y), with a / between when there are two values: x/y. There could be areas both aspect of the slash: x / y. The place just one worth is specified, it represents x, and the y worth is taken into account to be 1. So aspect-ratio: 1 is similar as aspect-ratio: 1/1, and aspect-ratio: 2 is similar as aspect-ratio: 2/1.

The aspect-ratio worth can embody the phrase auto — resembling aspect-ratio: auto 1/2. The auto worth will apply to changed components resembling pictures and movies. (In different phrases, the factor will hold its pure facet ratio.) The 1/2 ratio will apply to non-replaced components resembling divs.

Values can embody floating-point numbers resembling 0.5, as we noticed above. So aspect-ratio: 1.5/1 is legitimate, and is equal to aspect-ratio: 3/2.

We will additionally use var() and calc() as a part of aspect-ratio values, as seen above.

For non-replaced components like divs, we don’t must set a width for aspect-ratio to take impact. If a width or top is ready, facet ratio can be based mostly on that. If each width and top are set on a component, any aspect-ratio setting can be ignored. We will additionally run into surprising outcomes when making use of combos of width, top, max-width and min-width to containers together with aspect-ratio, as mentioned on this SitePoint discussion board thread.

It’s all the time harmful to set heights on container components, as this will simply result in content material spilling out of the container. Apparently, if we apply aspect-ratio to a container and the content material can’t match, the container will increase. So, because the specification says, aspect-ratio units a “most popular” constraint, relatively than a set one. We will override this by setting overflow to auto on the container.


The aspect-ratio property is nicely supported in all fashionable browsers now, so it’s protected to make use of. However if you wish to be extremely conservative and cater to a few of the older browser variations nonetheless floating round, the padding hack is a dependable fallback choice.

To learn extra in regards to the aspect-ratio property, take a look at the MDN reference, in addition to the W3C specification.

If you happen to’re eager to discover extra of the thrilling issues CSS can do as of late, I like to recommend you take a look at Unleashing the Energy of CSS, the place Stephanie Eckles presents all the wonderful, time-saving improvements which have landed in CSS of late.


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