Responsive iframes

tl;dr

Use the responsive iframe generator to quickly create a responsive iframe at any aspect ratio. Check out the code below to see how you can easily create them with just CSS using aspect ratio boxes.

.iframe-container {
  overflow: hidden;
  /* 16:9 aspect ratio */
  padding-top: 56.25%;
  position: relative;
}
.iframe-container iframe {
   border: 0;
   height: 100%;
   left: 0;
   position: absolute;
   top: 0;
   width: 100%;
}

<div class="iframe-container">
  <iframe src="//www.youtube.com/embed/KMYrIi_Mt8A" allowfullscreen></iframe>
</div>

Or you can use custom properties:

[style*="--aspect-ratio"] > :first-child {
  width: 100%;
}
[style*="--aspect-ratio"] > img {  
  height: auto;
} 
@supports (--custom:property) {
  [style*="--aspect-ratio"] {
    position: relative;
  }
  [style*="--aspect-ratio"]::before {
    content: "";
    display: block;
    padding-bottom: calc(100% / (var(--aspect-ratio)));
  }  
  [style*="--aspect-ratio"] > :first-child {
    position: absolute;
    top: 0;
    left: 0;
    height: 100%;
  }  
}

<div style="--aspect-ratio:815/419;">
</div>
<div style="--aspect-ratio:16/9;">
</div>
<!-- even single value -->
<div style="--aspect-ratio:1.4;">
</div>

Guide to Responsive iframes

You’ve spent countless hours designing and building the perfect responsive site. One problem — iframes. Proportionally resizing these pesky little windows to another world can be frustrating. It’s easy enough to make it span 100% of its container, but there’s no attribute (yet) to make the height resize accordingly.

So how do you keep from blowing your top trying to make an iframe responsive? Hint: it doesn’t require any JavaScript, just a simple CSS technique!

First, let’s define what a “responsive iframes” actually means.

What is a responsive iframe?

The term “responsive iframe” is a little broad. For instance, styling an iframe to use 100%, 100vw or 100vh is technically making it responsive. But what if you need to adjust its height based on the width so it keeps its aspect ratio? That’s where the problem is, iframes are fluid and can’t natively adapt.

The old way of building responsive iframes usually took the form of some nasty JavaScript hack. A better, modern way uses a simple CSS technique — intrinsic ratios — to create an aspect ratio box.

What is an aspect ratio box?

An aspect ratio is basically a container that adjusts its height based on its width to always keep its aspect ratio (i.e. 16×9, 4×3, 1×1, etc.). They’re most commonly used to embed iframe videos like YouTube or Vimeo videos.

This isn’t particularly new stuff. I think the original credit goes as far back as 2009 and Thierry Koblentz’s Intrinsic Ratios and maintained popularity even for other kinds of content with articles like Uncle Dave’s Ol’ Padded Box.

What is an intrinsic ratio?

An intrinsic ratio means an element will maintain its aspect ratio when resized. Think of an img with max-width: 100%. Change the width of its parent and it’ll change the size while keeping the same shape (aka. its aspect ratio).

How to calculate aspect ratios?

Perfect squares and 16:9 stuff is great, but the values used for those are just simple math. An aspect ratio can be anything, and they commonly are completely arbitrary. A video or image can be cropped to any size.

So how do you figure out the padding-top for say an image that’s 1127.34×591.44? One way is using the CSS calc(), like this:

padding-top: calc(591.44 / 1127.34 * 100%);

If you’re using a preprocessor like Sass, we could do the calculation ahead of time:

padding-top: 591.44px / 1127.34px * 100%;

How to create a responsive iframe?

It’s a cinch to make iframes responsive with an aspect ratio box using the intrinsic ratio technique. Or use the responsive iframe generator.

Create the aspect ratio box.

.iframe-container {
  overflow: hidden;
  /* 16:9 aspect ratio */
  padding-top: 56.25%;
  position: relative;
}

<div class="iframe-container"></div>

Position the iframe.

.iframe-container iframe {
   height: 100%;
   left: 0;
   position: absolute;
   top: 0;
}

<div class="iframe-container">
  <iframe src="https://www.youtube.com/embed/mB1dE0FotdY" width="100%" frameborder="0" title="Responsive iframe example" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen />
</div>

Optimize & style as needed.

.iframe-container iframe {
   border: 0;
   height: 100%;
   left: 0;
   position: absolute;
   top: 0;
   width: 100%;
}

<div class="iframe-container">
  <iframe src="https://www.youtube.com/embed/mB1dE0FotdY" loading="lazy" title="Responsive iframe example" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen />
</div>

Try resizing your browser window to see the responsive iframe in action.

List of ratios for responsive iframes.

Here’s a list of other aspect ratio percentages you can use when defining padding-top.

padding-top: 56.25%; /* 16:9 aspect ratio */
padding-top: 75%; /* 4:3 aspect ratio */
padding-top: 66.66%; /* 3:2 aspect ratio */
padding-top: 62.5%; /* 8:5 aspect ratio */
padding-top: 100%; /* 1:1 aspect ratio */

Responsive iframes with Sass

Sass makes it even easier to create responsive iframes. You can create a ratio function that’ll calculate the padding percentage needed for a particular aspect ratio, then a mixin to generate the styles.

The responsive iframe Sass mixin.

Use this Sass mixin to create an aspect ratio box for your iframes.

/// Aspect ratio box.
///
/// @author Ben Marshall
/// @link https://www.benmarshall.me/responsive-iframes
///
/// @param {int} $width - Width in pixels.
/// @param {int} $height - Height in pixels.
///
/// @example scss - Aspect ratio box mixin
///   .iframe-container {
///     @include aspectRatioBox(834, 469);
///   }
///
/// @output CSS aspect ratio box.
///   .iframe-container {
///     overflow: hidden;
///     padding-top: 56.25%;
///     position: relative;
///     top: 0;
///     width: 100%;
///   }
///
///   .iframe-container iframe {
///     border: 0;
///     height: 100%;
///     left: 0;
///     position: absolute;
///     top: 0;
///     width: 100%;
///   }
@mixin aspectRatioBox($width, $height) {
  overflow: hidden;
  padding-top: percentage($height / $width);
  position: relative;
  iframe {
    border: 0;
    height: 100%;
    left: 0;
    position: absolute;
    top: 0;
    width: 100%;
  }
}

The ratio Sass function.

Here’s a handy Sass function to calculate aspect ratio percentages:

/// Calculate a ratio.
///
/// @author Ben Marshall
/// @link https://www.benmarshall.me/responsive-iframes
///
/// @param {int} $width - Width in pixels.
/// @param {int} $height - Height in pixels.
/// @return {int} The calculated ratio percent.
///
/// @example scss - Ratio function
///   ratio(834, 469)
///   // 56.25
@function ratio($width, $height) {
  return percentage($height / $width);
}

CSS Framework Support

Many CSS frameworks like Bootstrap, Foundation, or Materialize have built-in styles for aspect ratio boxes. All use the same technique. Check out some of the examples below.

Responsive iframes in Bootstrap

Bootstrap 3.2+, uses the predefined class .embed-responsive, an aspect ratio class like .embed-responsive-16by9, and the .embed-responsive-item for the iframe. Check out the examples below or view their Embeds documentation.

<!-- 21:9 aspect ratio -->
<div class="embed-responsive embed-responsive-21by9">
  <iframe class="embed-responsive-item" src="..."></iframe>
</div>
<!-- 16:9 aspect ratio -->
<div class="embed-responsive embed-responsive-16by9">
  <iframe class="embed-responsive-item" src="..."></iframe>
</div>
<!-- 4:3 aspect ratio -->
<div class="embed-responsive embed-responsive-4by3">
  <iframe class="embed-responsive-item" src="..."></iframe>
</div>
<!-- 1:1 aspect ratio -->
<div class="embed-responsive embed-responsive-1by1">
  <iframe class="embed-responsive-item" src="..."></iframe>
</div>

Within Bootstrap’s _variables.scss, you can change the aspect ratios. Here’s an example of the $embed-responsive-aspect-ratios list:

$embed-responsive-aspect-ratios: (
  (21 9),
  (16 9),
  (4 3),
  (1 1)
) !default;

Responsive iframes in Materialize

If you are using Materialize CSS, then you don’t need your own classes either. Just add the .video-container class to your wrapper:

<div class="video-container">
  <iframe src="https://www.youtube.com/embed/K1K8s-tQGqY" frameborder="0" allowfullscreen></iframe>
</div>

Responsive iframes in Foundation

<div class="responsive-embed">
  <iframe src="https://www.youtube.com/embed/K1K8s-tQGqY" frameborder="0" allowfullscreen></iframe>
</div>

Aspect ratio modifier classes are set in your $responsive-embed-ratios map in your Foundation settings file:

$responsive-embed-ratios: (
  default: 16 by 9,
  vertical: 9 by 16,
  panorama: 256 by 81,
  square: 1 by 1,
);

Responsive iframes in Semantic UI

Semantic UI provides an embed module that allows you to create aspect ratio boxes for videos, iframes, and more. See their Embed documentation for more information.

$('.url.example .ui.embed').embed();

<div class="ui embed" data-url="https://www.youtube.com/embed/O6Xo21L0ybE" data-placeholder="/images/bear-waving.jpg"></div>

Responsive iframes in Bulma

In Bulma, you can apply a specific ratio on any element by applying the has-ratio modifier to a resizable element. Check out the example below or see their Arbitrary ratios with any element documentation.

For example, you can apply a 16by9 ratio on an iframe.

<figure class="image is-16by9">
  <iframe class="has-ratio" width="640" height="360" src="https://www.youtube.com/embed/YE7VzlLtp-4?showinfo=0" frameborder="0" allowfullscreen></iframe>
</figure>

Here’s a list of all the available Bulma aspect ration classes:

• is-square or is-1by1 – 1×1
• is-5by4 – 5×4
• is-4by3 – 4×3
• is-3by2 – 3×2
• is-5by3 – 5×3
• is-16by9 – 16×9
• is-2by1 – 2×1
• is-3by1 – 3×1
• is-4by5 – 4×5
• is-3by4 – 3×4
• is-2by3 – 2×3
• is-3by5 – 3×5
• is-9by16 – 9×16
• is-1by2 – 1×2
• is-1by3 – 1×3

What if the aspect ratio is dynamic?

This is the only time JavaScript should be used. Let’s say you have content authors creating interactives with each having different dimensions. Without knowing the aspect ratio of the iframe, it’s not easy to implement the intrinsic ratio technique.

You can overcome this problem by using JS. There’s a number of JS libraries out there (Pym.js or this jQuery plugin), or you can use this little code snippet.

function resizeAspectRatioBoxes() {
  var
    $this = $(this),
    proportion = $this.data('proportion'),
    w = $this.attr('width'),
    actual_w = $this.width();
  if (!proportion) {
    proportion = $this.attr('height') / w;
    $this.data('proportion', proportion);
  }
  if (actual_w != w) {
    $this.css('height', Math.round(actual_w * proportion) + 'px');
  }
}
$(window).resize(function() {
  resizeAspectRatioBoxes();
}):

Responsive iframes are awesome.

Say Goodbye to embedded content breaking your layouts with aspect ratio boxes using the intrinsic ratio technique. No longer do you have to deal with those annoying gaps iframe containers make as content width changes. Just keep in mind these tips when building aspect ratio boxes:

Things to remember.

• First, the content within the iframe must be responsive. If not, it defeats the purpose of creating an aspect ratio box.
• Don’t forget to specify the containers position to be relative. This allows the absolute positioning of the iframe within it.
• The padding-top value is calculated based on the aspect ratio of your content. You can calculate this value using: (height / width) * 100 = aspect ratio precent.
• height is set to 0 because padding-bottom gives the iframe it’s height.
• Using overflow: hidden is important because it ensures if any content does protrude outside of the container, it will be hidden and avoid screwing up the site’s layout.
• Like with most absolute positioned elements, we need to set the top and left properties so the iframe get’s put in the right place.
• Finally, width and height are set to 100% so the iframe takes up 100% of the containers’ space.

Using aspect ratio boxes is great for all kinds of content, not just iframes. We can use this same technique to make other types of embedded content responsive like Google Maps, calendars, Vimeo, and YouTube videos. Basically, anything that needs to keep its aspect ratio as the screen size changes. How are you using them on your site? Comment below.

FAQ

Do you have a question about aspect ratio boxes, the intrinsic ratio technique or how to make iframes responsive? Or maybe you have another nifty technique. I wanna hear from you. Post your questions, comments, or suggestions in the comments below.

More about iframes & aspect ratio boxes.

With the numerous screen sizes, there’s a host of things to consider to ensure your site looks good no matter the device. Not only is it important to consider the responsiveness of elements, but the performance too. Check out these other articles on iframes, responsive performance, and techniques to keep things sized right.

• Learn how to lazy-load iframes
• Responsive iframe Generator
• Resize Videos Proportionally with Intrinsic Ratios
• Responsive Images — 6 Simple Ways