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Line-height CSS How CSS line-height works and best practices

lampewebdev profile image Michael "lampe" Lazarski ใƒป3 min read

The line-height CSS property defines the space between two inline elements. The typical use is, to space-out text. You can see people comparing it to 'leading' which is a term used in typography that refers to the space between the baseline of two lines of text. line-height works differently. It adds space above and under the text.

leading vs line-height


Left: Leading, Right: line-height

Usage

You can use line-height with different values like this:

body {
    line-height: normal; /* default */
    line-height: 2;
    line-height: 1em;
    line-height: 1rem;
    line-height: 200%;
    line-height: 20px;
}

Oh boy ๐Ÿ˜ง! That's a lot. Let's get through them one by one ๐Ÿ‘.

Default value and unitless value

'normal' is the default value if you don't set it to something different. Usually, this means that it is set to 1.2, this depends on the browser vendor. So what does just a number value without any unit mean? It is actually a multiplier. It takes the font-size value and multiplies it by 1.2. Let's calculate the height of one line with the following example.

body {
    font-size: 16px;
    line-height: 1.5;
}

We just have to do the following calculation: 16 * 1.5 = 24px. So we now know that our text will have a minimum height of 24px. So it will add 4 pixels under the text and above it. Cool that easy ๐Ÿ˜Ž!

em and rem

Next one is em and rem. rem is relative to the font-size of the root element and em is relative to the current elements font-size. Here is an example

html {
    font-size: 12px;
}

.remExample {
    font-size: 16px;
    line-height: 1.5rem; /* line-height will be 12 * 1.5 = 18px */
}

.emExample {
    font-size: 16px;
    line-height: 1.5em; /* line-height will be 16 * 1.5 = 24px */
}

percentage

The % value is a little bit tricky to read. 100% means multiply by 1. Again an example to make it clear.

body {
    font-size: 12px;
}


.percentage {
    font-size: 16px;
    line-height: 150%; /* line-height will be 16 * 1.5 = 24px */
}

pixel (px)

The easiest also most confusing one for me is the px value. Setting it to any pixel value will set it to exactly this value. So if your font-size for example is 16px and you set line-height to 12px your font will be bigger then the container it is wrapped in. In general, you should try to avoid using px values in line-height!

body {
    font-size: 16px;
}

.pixel {
    line-height: 12px;
}

Some best practices

In general, I would start with setting the font-size and line-height in the body element to the following values.

body {
    font-size: 16px;
    line-height: 1.5;
}

From this, you can build all your other stylings. I would try to avoid using anything else then unitless numbers. Also, try to use a value for the font-size that easily divided, like 16 or 12. This will help you to keep balance in your design. You can use this in margins and paddings too. It's easier to calculate 16 * 1.5 in your head then for example 13 * 1.5. You then will always know what the actual value is.

body {
    font-size: 16px;
    line-height: 1.5;
}

h1, h2, h3, h4, ul, ol {
    margin-bottom: 15rem;
}

button {
    display: inline-block;
    padding: 0.75rem 1.5rem;
}

Of course, you can experiment with this and there will be exceptions to these rules but this is how I always start.

Resources

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Posted on Aug 21 '19 by:

lampewebdev profile

Michael "lampe" Lazarski

@lampewebdev

I'm a full-stack web developer. I love to help people.

Discussion

markdown guide
 

I think there's a mistake with the percentage definition. When you define line-height to 1.5% you don't multiply it by 1.5, you multiply it by 0.15.

Also it refers to the element it is defined, not the parent. 100% on the child would give a line-height value of 24px.

At least it's what I'm getting on Firefox. Is it different for you?

 

Your are right!
It should be 150%!

Yeah while I was writing this I was thinking for some reason about witdh or height. % in line-heigh refers to the font-size of the element.

Thank you!

 

Yes and it refers to the font-size of the element itself. I think that for .child to have a line-height of 24px it should have it set to 100%.

I just forgot to update the CSS ๐Ÿคฃ.

Now it should be correct!

Thanks again! appreciated it!

 

Thanks for the article!
One small thing I don't think is quite right. You say em is relative to the current element's font-size, but I believe it is actually the parent element's font-size. Which is why it can lead to unexpected results.

Here's a link to the example in the MDN Docs - MDN Docs Example of why to use unitless

 

In the example in MDN Docs, h1 element inherits line-height: 1.1em from its parent div element; Only in such circumstance the computed line-height of h1 would be 1.1 * its parent element's font-size;

 
 

Thanks so much for explaining line-height vs. leading, it just changed my life!

We spent months with a client who wanted the 'leading' just right, and this could have saved me a lot of trouble.

 

wow! for months?

Does he want it to be pixel perfect?

Web design is not paper. It will look a little bit different on each system/browser/monitor.

Even if you think of how an OS renders fonts. Linux, Windows, and OSX do have completely different implementations of how the render fonts.

So yeah it's not like paper where you print it once and it will be always the same on the same paper.

But was the client happy in the end?

I hope I changed your life for the better ;) Much appreciated.

 

She did not understand web design at the beginning, so they sent some files that were not very useful and they did not take into account responsiveness either. We spent a lot of the time explaining things to them.

Thankfully it all worked out :)

Yeah that happens you have to explain this to people that a browser window is not a piece of paper ๐Ÿ‘

 

Quick question / comment: Bearing in mind in print no 'leading' is added to the top line of a paragraph or text element, doesn't that mean thus that 'line-height' does in fact work the same way as leading when dealing with multiple lines in a paragraph? Won't they just end up with the equivalent amount of distance between the multiple lines as leading does?

 

Hey! Have a question. Most of design services (Adobe XD, Sketch) use "leading" and developers use "line-height" in CSS. So I'm designer and I work in Adobe XD now, which was chosen cos it gives a dev link with all the parameters etc. So my developer sees this "leading" parameter and he doesn't know how to convert it into "line-height" so he can make it pixel perfect.

Do you know how to convert "leading" into "line-height"? or how to code "leading" instead of "line-height"?

 

Hey!

I can not say this for every application. It depends on the default settings of the application.

Photoshop(maybe in XD it is the same) for example:

  • If it is not set then you should set line-height: 1.2;
  • If you have it set to any other value the calculation is as follows: font-size + (leading / 2) = line-height

Also a value you should set is line-spacing: Line Spacing = (Line Height - Font Size) / 2

I hope I could help you at least a little bit.

In general pixel-perfect is hard to do. Font rendering works different on every OS and even sometimes depends on the resolution of the monitor/phone.

 

Thank you, these are helpful things to me.

 

Glad I could help ๐Ÿ˜Š๐Ÿ‘

 

๐Ÿ‘๐Ÿป๐Ÿ‘๐Ÿป๐Ÿ‘๐Ÿป Good article.

Ps: rem is relative to the root element and the root element si html tag not body tag ( html { font-size: 14px; })