Choosing The Best CSS Units For A Responsive Web Layout

CSS units are one of the most fundamental aspects when it comes to creating a responsive website. These units determine how your website design and layout will interact with users on various devices and screens. When it comes to CSS, there are many options that you can choose from that are not just limited to fonts. As there are several options when it comes to choosing CSS units, that it might get overwhelming for some. Continue reading if you want to know how each unit affects the layout of your website.

How to Choose the Best CSS Units for Your Responsive Website Layout?

When it comes to website design, most people prefer to use CSS. And we cannot forget different CSS units when it comes to creating a responsive website layout. To help you choose the best CSS units below is everything you need to know about various units and their use in website design.

Choosing The Best CSS Units For A Responsive Web Layout 1

Types of CSS Units

CSS units can be divided into three main categories, as follows:

  • Absolute Units
  • Font relative Units
  • Viewport relative Units

Absolute Unit:

Absolute units are fixed across all devices and are not affected by various screen sizes and fonts. These units may vary depending on screen size resolutions because they depend on dots per inch (DPI) of the screen. These units include:

  • px (pixels)
  • in (inches)
  • cm (centimetre)
  • mm (millimeter)
  • pc (picas)
  • pt (Points)

Out of all the above mentioned absolute CSS units, the pixel is the most commonly used measurement in website design and is the most accepted one. One of the reasons behind its frequent use is that it provides a consistent result on various devices, which means it is relative to the viewing device. Pixel is great for creating a border since we want it to be the same on different screens.


According to this example, the box element of the layout will have a height and width of 100px that will remain the same on various screen sizes. It is highly recommended to consult a web development company in Dubai regarding the relationship of real-world measurements like cm, mm with CSS units. This way, you can have a well-designed layout.

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Font Relative Units

Font relative units depend upon the font size, family, or parent elements. In other words, these units don’t have a fixed size like absolute units. Website developers prefer these units because they quickly adjust to different screens of various sizes. These include:

  • Em
  • Rem
  • Ex
  • Ch
  • Percentage %

We will discuss some of the preferred CSS units for a responsive website design.

Choosing The Best CSS Unit For A Responsive Web Layout

Em is a relative length unit that depends upon the font size of the document or parent element. As it is relative to the immediate parent, using it for font sizes can lead to unexpected results. For example, if a parent element has a font size of 18px, then for all its child’s 1em will be measured as 18px, and 2em will be 36px.

background-color: rgb(70, 43, 220);
.box h1{
.box p{
Font-size: 1em;

Unlike em, rem is relative to the root elements of HTML instead of the parent elements. It is a scalable
CSS unit used for font sizes and is highly recommended for responsive website. In the above example, if you change the units from em to rem, you will see all child elements will fix themselves.

For example:

background-color: pink;
.box h1{
.box p{
Font-size: 1rem;

Ex unit is related to the x-height of the current font used and is not very commonly used in website design. The height is not very consistent s it can come from the font or is calculated by the browser itself. It is just like em and rem, and the only difference is that when you change the font family, the ex will change automatically.


This unit is similar to the ex, but it doesn’t depend on x-height. It relies on the width of the zero characters.

Percentage %

A percentage unit is a relevant unit which depends upon the parent elements and is mostly used for the width and height of elements. The percentage CSS unit is commonly used for a fluid or a responsive base layout.

body {
background-color: blueviolet;

img {
width: 50%;

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Choosing The Best CSS Units For A Responsive Web Layout 2

Viewport Relative Units

The viewport units depend on the height and width of the viewport. These include the following:

  • Vh
  • Vw
  • Vmin
  • Vmax

The details are given below:

Vh (Viewport Height)

1Vh is equal to 1% of the viewport height. This unit is highly useful in creating elements of full height. It is very similar to the percentage unit, but it does not depend upon parent elements and is relative to the viewport that is the browser window.

For example, if you want to create a pink box of 100% height in the viewport, use the following:

Vw (Viewport Width)

Similarly, Vw is similar to Vh, but it deals with the viewport’s width and not the height. For example:


In this example, the font-size is 5% of the viewport width. It means that if the viewport’s width is 1000px, the font size will be 50%, and so on. It is beneficial CSS unit in building a responsive website layout, so make sure to consult with Spiral Click, a web development company in Dubai, to ensure proper coding of your online platforms. 


Vmin is calculated based on the minimum value of the width or height of the viewport. Let’s say the size of the viewport is 1000px in height and 800px in width. 1Vmin, in this case, will be equal to 8px.


Similarly, Vmax is calculated based on the maximum value of viewports height and width. Like the previous example for Vmin, the size of the viewport is 1000px tall and 800px wide. Then 1Vmax will be equal to 10px. You can use these as follows:

background yellow;

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Know your CSS Unit Options!

These are almost all the CSS units available for use for creating a responsive web layout. As a website developer, it is always good to know your options and choose the ones that suit your design goal. These units will give you the desired result, but do ensure expert help, so there are no problems in the codes, and your layout is responsive.

There is no hard and fast rule for using CSS units when designing a responsive website layout. But, coding is for not everyone, so outside help is highly recommended.

Also read: 5 Things You Must Know Before Designing a Logo

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