CSS font-size: A Definitive Font-Sizing Guide

CSS font size setting seems simple, but it is challenging to actually operate. Many developers rely on repeated adjustments to the font-size attributes to achieve visual effects, but find that the rendering results of different browsers are inconsistent. A deep understanding of CSS font size settings will result in twice the result with half the effort.

Key Points

• CSS font-sizeProperties accept a variety of parameters, including absolute, relative, and length values. Unless explicitly overridden, elements inherit the font size of the parent element, which is crucial in specifying the relative size.
• While absolute font size keywords can be used, their exact size can vary greatly across browsers, so developers usually avoid this rough approach. Relative Font Size Keywords adjust the font size according to the parent element size. You can set the font size with absolute length values, but you can also encounter some problems, and despite potential accessibility issues, pixel values ​​are still the most appropriate.
• Developers generally believe that in most cases, using em or % units is the best solution for dealing with web fonts, as they scale accurately with each other and support browser text resizing. It is recommended to use percentage font size on the tags to make text resizing better in older browsers.

font-sizeProperties

The

font-size attribute can be used for any HTML tag (even if it does not usually contain text content, such as <br>). It can assign various absolute, relative, or length value parameters. The element will inherit the parent element's font-size unless you override it. This is especially important when you specify a relative size.

Absolute Font Size Keywords

Multiple absolute font size keywords can be used. The font size is determined by the browser's presets, and the element will not inherit the size of the parent element.

• font-size: xx-small;
• font-size: x-small;
• font-size: small;
• font-size: medium;
• font-size: large;
• font-size: x-large;
• font-size: xx-large;

Although most browsers support these keywords, the exact size will vary. They are a rather rough way to set font sizes, which most developers will generally avoid.

Relative Font Size Keywords

Two relative font size keywords can be used. Font size is determined based on its parent element size:

• font-size: smaller;
• font-size: larger;

For example, if the parent element's font size is "medium", the "larger" value will set the element to "large". Other font units are usually adjusted to a coefficient of about 1.2, but again, there is no standard and the browser results will be different.

Absolute length

font-sizeAttributes can assign absolute length:

• mm: mm, for example 10mm.
• cm: cm, e.g. 1cm (= 10mm).
• in: inches, for example 0.39in (~= 10mm).
• pt: Pounds, 1pt is usually assumed to be 1/72 inch, e.g. 12pt.
• pc: Card is 12pt for 1pc.
• px: Pixels, for example 14px.

Generally speaking, there are problems with all these units of measurement. Millimeters, centimeters and inches are inaccurate for screen-based media. Pounds and pokers are unreliable because the system can use different dpi settings. Pixels seem to fit the most, but it can cause accessibility issues as text cannot be resized in IE.

Relative length

font-sizeAttributes can assign units relative to their parent element font size:

• em: 1em is equal to the current font size, so 2em is twice the size.
• %: 100% equals the current font size, so 200% is twice the size.
• ex: 1ex is equal to the height of the letter "x" in the current font.

Few developers use "ex", but it can be useful in some cases where fine-grained font sizes are required, such as 1ex instead of 0.525em. Percentage and em size are equivalent, such as 50% = 0.5em, 100% = 1em, 120% = 1.2em, etc. Some browsers will show subtle differences, but this is rarely a major issue. If you want to save every byte, you can choose the shortest definition, i.e. 50% shorter than 0.5em and 1em shorter than 100% shorter.

Text size and page zoom

This is where the extra complexity comes. Most browsers allow users:

1. Increase or decrease the basic text size (image size remains unchanged)
2. Zoom in or out of the page so that all text and graphics change accordingly, or
3. Also allow text resizing and page scaling.

To further complicate things, Internet Explorer does not allow text resizing elements whose font size is defined in pixels (px). If you are a developer who has moved from a typographic background to web design, it is disturbing to give users such a lot of power. Your design may be broken by the user magnification by 200% but reduce the text size to 50%. And – no – you can’t stop it. You shouldn't stop it either.

CSS font size recommendations

It is generally believed that in most cases, em or % is the best solution. Web fonts can be accurately scaled to each other and support browser text resizing. I also recommend using percentage font size on the tag; this will result in better text resizing in some older browsers. When developing a website, I also recommend that you make the following suggestions:

1. Reset font size and page scaling to default values ​​in all browsers before testing (it caught me off guard several times!)
2. Try using reasonable text size and page scaling combinations in various browsers to ensure text remains readable.

Have font size ever caused you problems? Do you have any other tips?

CSS Font Size FAQs (FAQs)

What is the difference between absolute font size and relative font size in CSS?

In CSS, the font size can be set using absolute or relative values. The absolute value is fixed and will not change according to the size of the parent element. They are defined in units such as pixels (px), pounds (pt), or centimeters (cm). On the other hand, the relative values ​​are dynamic and will change according to the size of the parent element. They are defined using units such as em, rem, or percentage (%). The choice of absolute font size and relative font size depends on the design requirements and the responsiveness of the web page.

How does em units work in CSS font size?

em units are scalable units used for font size in CSS. It has the font size relative to its nearest parent element. For example, if the parent element's font size is 20px, "1em" will equal 20px for the child element of that element. If the font size is not defined, the default value is usually 16px, so "1em" will be 16px.

How to use rem units to set font size?

rem unit represents "root em". It is relative to the root element (html) rather than the parent element. This means that 1rem is equal to the font size of the root element. If the font size of the root element is 16px (the default size for most browsers), 1rem will equal 16px.

What are the vw units in the CSS font size?

vw units represent viewport width. It is relative to the width of the viewport, where 1vw is equal to 1% of the viewport width. This unit allows font size to be adjusted according to screen width, making it an excellent tool for responsive design.

How to make my font size responsive using CSS?

To make your font size responsive, you can use relative units such as em, rem, or vw. These units adjust the font size according to the size of the parent element, the size of the root element, or the viewport width. This allows font size to change dynamically based on screen size or the size of parent element.

How does the

function in the CSS font size work? calc() The

function in

in CSS allows you to perform calculations to determine the font size. It can be used with different units, making it a powerful tool for creating responsive designs. For example, you can set a font size using calc() which is a mixture of fixed pixel values ​​and relative viewport values. calc() What is the impact of the

attribute in

in CSS? font-size-adjust The

attribute in

in CSS allows you to adjust the x-height of the font (the height of lowercase letters). This is useful when you use alternate fonts because it ensures that x height is retained, and that readability is consistent no matter which font is used. font-size-adjust

How to use ch units in CSS font size?

The width of the ch unit in CSS relative to the font "0" (zero) width of the font used. This unit is useful when you want to set the width of an element based on the characters contained in it, such as setting the width of a button based on the length of the internal text.

What is the lh unit in the CSS font size?

lh unit represents "Ride height". Its row height relative to the element. This unit is useful when you want to set the height of an element based on the row height, such as creating a vertical rhythm in your design.

How to use ex units in CSS font size?

The ex unit in CSS relative to the x height of the current font. x height is usually the height of lowercase letters (such as "x"). This unit is useful when you want to set the height of an element based on x height, such as vertically aligning elements based on internal text.

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