Fit Div Size to Background Image

Scale div to fit background image

Let a transparent image dictate the DIV dimensions.

Inside that div put the same image with CSS opacity: 0

<div id="mainHeaderWrapper">
   <img src="path/to/image.jpg"><!-- I'm invisible! -->
</div>

set that image to

#mainHeaderWrapper {
    background: no-repeat url(path/to/image.jpg) 50% / 100%;
}
#mainHeaderWrapper img {
    vertical-align: top;
    width: 100%; /* max width */
    opacity: 0;  /* make it transparent */
}

That way the height of the DIV will be dictated by the containing invisible image, and having the background-image set to center, full (50% / 100%) it will match that image's proportions.

Need some content inside that DIV?

Due to the containing image, you'll need an extra child element that will be set to position: absolute acting as an overlay element

<div id="mainHeaderWrapper">
   <img src="path/to/image.jpg"><!-- I'm invisible! -->
   <div>Some content...</div>
</div>

#mainHeaderWrapper{
    position: relative;
    background: no-repeat url(path/to/image.jpg) 50% / 100%;
}
#mainHeaderWrapper > img{
    vertical-align: top;
    width: 100%; /* max width */
    opacity: 0;  /* make it transparent */
}
#mainHeaderWrapper > div{
    position: absolute;
    top: 0;
    width: 100%;
    height: 100%;
}

Fit background image to div

You can achieve this with the background-size property, which is now supported by most browsers.

To scale the background image to fit inside the div:

background-size: contain;

To scale the background image to cover the whole div:

background-size: cover;

JSFiddle example or runnable snippet:

#imagecontainer {
  background: url("http://3.bp.blogspot.com/_EqZzf-l7OCg/TNmdtcyGBZI/AAAAAAAAAD8/KD5Y23c24go/s1600/homer-simpson-1280x1024.jpg") no-repeat;
  width: 100px;
  height: 200px;
  border: 1px solid;
  background-size: contain;
}

<div id="imagecontainer"></div>

How to get div height to auto-adjust to background size?

Another, perhaps inefficient, solution would be to include the image under an img element set to visibility: hidden;. Then make the background-image of the surrounding div the same as the image.

This will set the surrounding div to the size of the image in the img element but display it as a background.

<div style="background-image: url(http://your-image.jpg);">
 <img src="http://your-image.jpg" style="visibility: hidden;" />
</div>

CSS background image to fit height, width should auto-scale in proportion

background-size: contain;

suits me

Force div to have the size of background image

Well, the reason why this is?

In your working example you use content. A content has it's own height and uses up space, which the other elements on the page have to respect.

With the background-image solution, you use a background, which does not use space. The .imageContainer2 element can not know about the height of the background-image AND adapt itself to it.

This very problem was addressed here: How to get div height to auto-adjust to background size?

Just check, if the workaround is suitable for you