Scale a div to fit in window but preserve aspect ratio

Question

How can I scale a div to fit inside the browser view port but preserve the aspect ratio of the div. How can I do this using CSS and/or JQuery?

Maxilliped

I provided the solution for this here: #644000 – Lumpkin

Can you accept an answer below? Seems a shame some very good answers go unaccepted – Hoi

Not a single one of the answers to this question achieve the desired result. Preserving the aspect ratio is trivial but getting it to be the correct aspect ratio AND always fitted to or smaller than the viewable area in both directions is more tricky. – Stakeout

Top answer here (from Danield) is the best solution : #20590739 – Stakeout

Answer 1

You don't need javascript for this. You can use pure CSS.

A padding-top percentage is interpreted relative to the containing block width. Combine it with position: absolute on a child element, and you can put pretty much anything in a box that retains its aspect ratio.

HTML:

<div class="aspectwrapper">
  <div class="content">
  </div>
</div>

CSS:

.aspectwrapper {
  display: inline-block; /* shrink to fit */
  width: 100%;           /* whatever width you like */
  position: relative;    /* so .content can use position: absolute */
}
.aspectwrapper::after {
  padding-top: 56.25%; /* percentage of containing block _width_ */
  display: block;
  content: '';
}
.content {
  position: absolute;
  top: 0; bottom: 0; right: 0; left: 0;  /* follow the parent's edges */
  outline: thin dashed green;            /* just so you can see the box */
}

The display: inline-block leaves a little extra space below the bottom edge of the .aspectwrapper box, so another element below it won't run flush against it. Using display: block will get rid of it.

Thanks to this post for the tip!

---

Another approach relies on the fact that browsers respect an image's aspect ratio when you resize only its width or height. (I'll let google generate a 16x9 transparent image for demonstration purposes, but in practice you would use your own static image.)

HTML:

<div class="aspectwrapper">
  <img class="aspectspacer" src="http://chart.googleapis.com/chart?cht=p3&chs=160x90" />
  <div class="content">
  </div>
</div>

CSS:

.aspectwrapper {
  width: 100%;
  position: relative;
}
.aspectspacer {
  width: 100%; /* let the enlarged image height push .aspectwrapper's bottom edge */
}
.content {
  position: absolute;
  top: 0; bottom: 0; right: 0; left: 0;
  outline: thin dashed green;
}

Telephone

can you put up a jsFiddle example with a perfect box (all sides euqal) resizing using the first method? I didn't quite get how it can be done using your first method. – Packer

Here you are: jsfiddle.net/ks2jH/1 Note that the key to making it a perfect box is the padding-top: 100% which means the height should be 100% of the size of the .aspectwrapper width. Since that width is set to 50%, it will resize with its parent. I also added overflow: hidden so the text wouldn't deform the box at small sizes. – Monastery

If you wanted a rectangle half as tall as it is wide, you would use padding-top: 50%. In my example above, I made a 16:9 rectangle, suitable for wide screen video, using padding-top: 56.25% (9/16 = 56.25%). – Monastery

great, thanks! you should update your answer to include this test page – Packer

this only seems to resize against the width. so it doesn't resize the width of the div so that the height fits. so it is not really fit-into-viewport but just rather boring old easy to achieve aspect ratio maintain. – Demonstrator

@LassiKinnunen Hint: You can build more complex things out of simpler things. – Monastery

@Telephone sure you can, but it doesn't seem to do what the topic of this question is. I've forgot the exact scenario I needed it for, but I think the thing was that I had a div and had to take that div and just plonk it inside another for one reason or another so that it fit entirely and whichever side didn't fit was made to fit while the other side was scaled in the same aspect. not that the other answers in this thread are too great either mind you. – Demonstrator

One very useful addition to the first variant: if you use padding-top: 25% in .aspectwrapper::after and max-width: 400vh in .aspectwrapper, the aspect wrapper fits not only the width of the viewport, but also its height (whichever constrains more). This is extremely useful when scaling a mostly fixed layout like presentation slides. – Photochromy

Answer 2

Thanks to Geoff for the tip on how to structure the math and logic. Here's my jQuery implementation, which I'm using to size a lightbox so it fills the window:

var height = originalHeight;
var width = originalWidth;
aspect = width / height;

if($(window).height() < $(window).width()) {
    var resizedHeight = $(window).height();
    var resizedWidth = resizedHeight * aspect;
}

else { // screen width is smaller than height (mobile, etc)
    var resizedWidth = $(window).width();
    var resizedHeight = resizedWidth / aspect;      
}

This is working well for me right now across laptop and mobile screen sizes.

Cammycamomile

Your check of height < width is only correct for an aspect ratio of 1:1. – Mordvin

with little refinery this works, but your IF doesnt check for the right thing var vw=$("#absoluteSized").width(); var vh=$("#absoluteSized").height(); var divAspect=vw/vh; if(divAspect > aspect) { resizedHeight = vh; resizedWidth = resizedHeight * aspect; } else { // screen width is smaller than height (mobile, etc) resizedWidth = vw; resizedHeight = resizedWidth / aspect; } – Demonstrator

@TRMW, please fix your answer per the comments, otherwise it should be considered wrong. – Cull

Answer 3

I have a different pure HTML/CSS approach which does not rely on padding or absolute positioning. Instead it uses em units and relies on the CSS min() function plus a little bit of math.

Imagine that we want a viewport div with 16:9 aspect ratio which always fits the browser window and is centered in the axis with excess space. Here's how we can accomplish that:

HTML

  <body>
    <div class="viewport">
      <p>
        This should be a 16:9 viewport that fits the window.
      </p>
    </div>
  </body>

CSS

body {
  width: 100vw;
  height: 100vh;
  margin: 0;
  display: flex;
  justify-content: center;
  align-items: center;
  background-color: white;
  font-size: min(1vw, 1.778vh);
}

div.viewport {
  width: 100em;
  height: 56.25em;
  background-color: lightblue;
}

div.viewport > p {
  font-size: 3em;
  text-align: center;
}

You can experiment with this in a sample JSFiddle here.

The secret sauce is in the body font-size. It should be set to min(1vw, Avh), where A is the aspect ratio you want the div to have, i.e. width / height. In the example above we're using 1.778, which is approximately 16 / 9.

In CSS, em units are based on the font-size of the element, which is inherited from parent element if not explicitly set. For your viewport div, set the width to 100em (NOT rem) and the height to Iem, where I is the inverse of the aspect ratio expressed as a percentage, i.e. 100 / A or 100 * height / width. In the example above we're using 56.25, which is 100 * 9 / 16.

One bonus of this approach is that all of your nested elements may also use em units so that they always scale precisely with the size of the viewport. You can see this used on the p element in the example.

Note that as an alternative to the above, you may set the font-size on your html element and use rem units everywhere. CSS rem units are similar to em units but always relative to the root element's font-size.

Exemplify

This should be the accepted answer as it does what was originally asked perfectly with the cleanest code. What an elegant solution. Thank you. – Diastasis

Answer 4

Javascipt:

//Responsive Scaling
let outer = document.getElementById('outer'),
wrapper = document.getElementById('wrap'),
maxWidth  = outer.clientWidth,
maxHeight = outer.clientHeight;

window.addEventListener("resize", resize);
resize();

function resize(){
let scale,
width = window.innerWidth,
height = window.innerHeight,
isMax = width >= maxWidth && height >= maxHeight;

scale = Math.min(width/maxWidth, height/maxHeight);
outer.style.transform = isMax?'':'scale(' + scale + ')';
wrapper.style.width = isMax?'':maxWidth * scale;
wrapper.style.height = isMax?'':maxHeight * scale;
}

HTML:

<div id="wrap">
<div id="outer">
{{ fixed content here }}
</div>
</div>

Styling:

/* Responsive Scaling */
#wrap {
  position: relative;
  width: 1024px;
  height: 590px;
  margin: 0 auto;
}
#outer {
  position: relative;
  width: 1024px;
  height: 590px;
  transform-origin: 0% 0%;
  overflow: hidden;
}

Diatomaceous

Some explanation and/or a Codepen would make this a great answer. – Cull

Answer 5

This is possible with JQuery and a bit of maths.

Use JQuery to get the view ports width and height as well as the divs current dimensions.

$(document).width();

Calculate the divs current aspect ratio. eg width/height

You need a bit of logic to determine whether to set the width or height first, then use the initial ratio to calculate the other side.

Faubert

+1 for providing the simple math route rather than the plugin route. – Britton

Answer 6

jQuery has a plugin that grows an object until one of its sides reaches a certain px-value. Coupling this will the viewport's height, you could expand any element to that size: jQuery MaxSide.

January

Answer 7

2024 Update:

Javascript is not needed. Nor, nowadays, is using em and min() to have the desired effect.

Use the css aspect-ratio property instead:

https://developer.mozilla.org/en-US/docs/Web/CSS/aspect-ratio

html

  <body>
    <div class="viewport">
      <p>
        This should be a 16:9 viewport that fits the window.
      </p>
    </div>
  </body>

css

.viewport {
   width: 100%;
   height: auto; /* at least one dimension must be auto */
   aspect-ratio: 16 / 8;
}

Johannesburg