If you're familiar with web development and site design using CSS, you've probably heard of CSS units. These units of measurement are essential for defining the size, position and other attributes of elements on a web page. In this article, we will explore what CSS units are, how they are used, and why they are important in web development.
What is a unit in CSS?
In CSS, a unit is a measurement used to define attributes such as size, position, margins, or spaces between elements. These units act as references that tell the browser how to render elements on the screen.
There are different types of CSS units, and each one has its particularities. The most commons are:
- Pixels (px): It is the most used unit and is considered an absolute unit, since its size will always be the same regardless of the screen resolution.
- Percentage (%) – Used in relation to the parent element and is especially useful when you need to make an element occupy a percentage of the width or height of its container.
- Em (em): This unit is based on the font size of the parent element and is especially useful when you want to set sizes relative to the font.
What are measurement units in CSS?
Measurement units in CSS are those used to define the size of elements. These units are necessary to ensure that your elements are viewed and positioned correctly on the screen.
The most used units of measurement in CSS are:
- Pixels (px): This is the most basic unit and is used to define fixed sizes.
- Percentage (%): Used to define sizes relative to the parent elements.
- Em (em): Used to define sizes relative to the font size of the parent element.
- Rem (rem): Similar to the Em unit, but based on the font size of the root element.
It is important to note that by using relative units such as percentage, Em or Rem, your elements will be more flexible and adapt better to different screen sizes and devices.
How to use CSS units in your project?
To use CSS units in your project, you simply indicate the unit after the numerical value. For example:
.footer { font-size: 20px; margin-top: 40px; width: 75%; }
In the example above, the unit "px" is used to define the font size and top margin, while the percentage is used to define the width of the element.
Remember that CSS units allow you to have greater control over the sizes and position of elements on your web page. It is advisable to use relative units that adapt to different devices and screens, and avoid excessive use of absolute units, which can distort the display on devices with different resolutions.
Frequently asked questions
When should you use absolute units in CSS?
Absolute units, such as pixels (px), can be useful in specific situations where you need to have precise control over the size of elements. However, keep in mind that when using absolute units, you may encounter display problems on devices with different resolutions.
What CSS units are most recommended for responsive design?
For responsive design, it is recommended to use relative units, such as percentage (%), Em or Rem. These units adapt to different screen sizes and allow your elements to be viewed and positioned correctly on mobile and desktop devices.
How can I convert absolute units to relative in CSS?
Converting from absolute to relative units in CSS can be a manual process and requires adjusting the values to be proportional to the size of the container or font. For example, you can use the formula relative value = absolute value / container size (source) to convert pixels to percentage or Em.
In conclusion, CSS units are essential for web design and development, as they allow sizes and positions to be defined in a precise and adaptable way. Using relative units such as percentage, Em or Rem is recommended to achieve a responsive design adapted to different devices and resolutions.
If you liked this article and want to learn more about web development and design, visit my website nelkodev.com. You can also contact me through this link or consult my portfolio at this other link.
English 
Spanish