How to Scale Text Size Compared to Container

Font scaling based on size of container

If the container is not the body, CSS Tricks covers all of your options in Fitting Text to a Container.

If the container is the body, what you are looking for is Viewport-percentage lengths:

The viewport-percentage lengths are relative to the size of the initial containing block. When the height or width of the initial containing block is changed, they are scaled accordingly. However, when the value of overflow on the root element is auto, any scroll bars are assumed not to exist.

The values are:

• vw (% of the viewport width)
• vh (% of the viewport height)
• vi (1% of the viewport size in the direction of the root element's inline axis)
• vb (1% of the viewport size in the direction of the root element's block axis)
• vmin (the smaller of vw or vh)
• vmax (the larger or vw or vh)

1 v* is equal to 1% of the initial containing block.

Using it looks like this:

p {
    font-size: 4vw;
}

As you can see, when the viewport width increases, so do the font-size, without needing to use media queries.

These values are a sizing unit, just like px or em, so they can be used to size other elements as well, such as width, margin, or padding.

Browser support is pretty good, but you'll likely need a fallback, such as:

p {
    font-size: 16px;
    font-size: 4vw;
}

Check out the support statistics: http://caniuse.com/#feat=viewport-units.

Also, check out CSS-Tricks for a broader look: Viewport Sized Typography

Here's a nice article about setting minimum/maximum sizes and exercising a bit more control over the sizes: Precise control over responsive typography

And here's an article about setting your size using calc() so that the text fills the viewport: http://codepen.io/CrocoDillon/pen/fBJxu

Also, please view this article, which uses a technique dubbed 'molten leading' to adjust the line-height as well. Molten Leading in CSS

How to scale text size compared to container

Here is a way to set the text to fit the width of the container. It works by incrementally increasing the font size of a hidden div until it is smaller than the width of the container for which you want to text to fit inside. It then sets the font size of the container to that of the hidden div.

This is a little inefficient and could be optimized by caching the old width of the container, then incrementing from the old font size to either larger or smaller values based on how the width of the container changed.

jsFiddle: http://jsfiddle.net/sarathijh/XhXQk/

<div class="scale-text styles">
    This is a test of scaling text to fit the container. Lorem Ipsum Dolor Sit Amet.
</div>
<div id="font-metrics"></div>

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.11.0/jquery.min.js"></script>
<script>
    var fontMetrics = document.getElementById('font-metrics');
    var scaleTexts  = $('.scale-text');

    $(window).on('resize', updateFontSize);
    updateFontSize();

    function updateFontSize()
    {
        scaleTexts.each(function()
        {
            var $scaleText = $$(this);

            fontMetrics.innerHTML = this.innerHTML;
            fontMetrics.style.fontFamily = $scaleText.css('font-family');
            fontMetrics.style.fontWeight = $scaleText.css('font-weight');
            fontMetrics.style.fontStyle = $scaleText.css('font-style');
            fontMetrics.style.textTransform = $scaleText.css('text-transform');

            var fontSize = 50; // max font-size to test
            fontMetrics.style.fontSize = fontSize + 'px';

            while ($$(fontMetrics).width() > $scaleText.width() && fontSize >= 0)
            {
                fontSize -= 1;
                fontMetrics.style.fontSize = fontSize + 'px';
            }

            this.style.fontSize = fontSize + 'px';
        });
    }

    /**
     * A simple caching function for jQuery objects.
     */
    function $$(object)
    {
        if (!object.jquery)
            object.jquery = $(object);

        return object.jquery;
    }
</script>

how to set font size based on container size?

You may be able to do this with CSS3 using calculations, however it would most likely be safer to use JavaScript.

Here is an example: http://jsfiddle.net/8TrTU/

Using JS you can change the height of the text, then simply bind this same calculation to a resize event, during resize so it scales while the user is making adjustments, or however you are allowing resizing of your elements.

Resize font-size according to div size

In regards to your code, see @Coulton. You'll need to use JavaScript.

Checkout either FitText (it does work in IE, they just ballsed their site somehow) or BigText.

FitText will allow you to scale some text in relation to the container it is in, while BigText is more about resizing different sections of text to be the same width within the container.

BigText will set your string to exactly the width of the container, whereas FitText is less pixel perfect. It starts by setting the font-size at 1/10th of the container element's width. It doesn't work very well with all fonts by default, but it has a setting which allows you to decrease or increase the 'power' of the re-size. It also allows you to set a min and max font-size. It will take a bit of fiddling to get working the first time, but does work great.

http://marabeas.io <- playing with it currently here. As far as I understand, BigText wouldn't work in my context at all.

For those of you using Angularjs, here's an Angular version of FitText I've made.

---

Here's a LESS mixin you can use to make @humanityANDpeace's solution a little more pretty:

@mqIterations: 19;
.fontResize(@i) when (@i > 0) {
    @media all and (min-width: 100px * @i) { body { font-size:0.2em * @i; } }
    .fontResize((@i - 1));
}
.fontResize(@mqIterations);

And an SCSS version thanks to @NIXin!

$mqIterations: 19;
@mixin fontResize($iterations) { 
    $i: 1; 
    @while $i <= $iterations { 
        @media all and (min-width: 100px * $i) { body { font-size:0.2em * $i; } } 
        $i: $i + 1; 
    }
} 
@include fontResize($mqIterations);

Change font size based on container

There's a great npm package called fitty that will fit the text to the size of the container automatically:

<div id="my-element">Hello World</div>

<script src="fitty.min.js"></script>
<script>
    fitty('#my-element');
</script>

Font scaling based on size of container

If the container is not the body, CSS Tricks covers all of your options in Fitting Text to a Container.

If the container is the body, what you are looking for is Viewport-percentage lengths:

The viewport-percentage lengths are relative to the size of the initial containing block. When the height or width of the initial containing block is changed, they are scaled accordingly. However, when the value of overflow on the root element is auto, any scroll bars are assumed not to exist.

The values are:

• vw (% of the viewport width)
• vh (% of the viewport height)
• vi (1% of the viewport size in the direction of the root element's inline axis)
• vb (1% of the viewport size in the direction of the root element's block axis)
• vmin (the smaller of vw or vh)
• vmax (the larger or vw or vh)

1 v* is equal to 1% of the initial containing block.

Using it looks like this:

p {
    font-size: 4vw;
}

As you can see, when the viewport width increases, so do the font-size, without needing to use media queries.

These values are a sizing unit, just like px or em, so they can be used to size other elements as well, such as width, margin, or padding.

Browser support is pretty good, but you'll likely need a fallback, such as:

p {
    font-size: 16px;
    font-size: 4vw;
}

Check out the support statistics: http://caniuse.com/#feat=viewport-units.

Also, check out CSS-Tricks for a broader look: Viewport Sized Typography

Here's a nice article about setting minimum/maximum sizes and exercising a bit more control over the sizes: Precise control over responsive typography

And here's an article about setting your size using calc() so that the text fills the viewport: http://codepen.io/CrocoDillon/pen/fBJxu

Also, please view this article, which uses a technique dubbed 'molten leading' to adjust the line-height as well. Molten Leading in CSS

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