Explain the difference between `px`, `pt`, and `pc` units
Jul 22, 2025 am 02:48 AMpx, pt, and pc are common units in web design and typography, but have different uses. 1.px (pixels) is the basic unit of screen display, used for front-end layout, such as font size, margins and element size. The advantages are good compatibility and support consistent scaling; 2.pt (dot) is a printing unit, 1pt=1/72 inch, suitable for printing style and PDF layout, but the screen display is affected by the device; 3.pc (pick card) is a larger printing unit, 1pc=12pt, which is rarely used now, because of poor readability and compatibility, there is no obvious advantage. Understanding the differences will help to select units reasonably according to project needs.
In web design and typesetting, px
, pt
, and pc
are common units of size, but their uses and manifestations are not the same. Simply put:

-
px
is the basic unit of screen display -
pt
is more inclined to print and physical size -
pc
is a relatively large printing unit with a low frequency of use.
Let’s take a look at the differences and applicable scenarios between them.
What is px
? Why is it important?
px
(pixels) is the unit most commonly used in web development, especially in front-end layouts. It represents a point on the screen, which is usually considered the "minimum display unit".

On modern screens, 1px does not necessarily equal a physical pixel, especially on high-definition screens (such as Retina screens), multiple physical pixels may be used to render pixels in a CSS. This is called the "device pixel ratio".
Common usage:

- Set the font size
- Control margins, padding
- Layout element width and height
advantage:
- Precise control
- Good compatibility on different devices
- Supports consistent performance when scaling
What is pt
? Which scenarios are suitable for?
pt
(dot) is a traditional printing unit, 1pt = 1/72 inches. It is more used in print styles or designs that require precise physical dimensions.
For example, if you want a text to be printed as 12pt font size, you can use pt
to define the font size.
Common usage:
- Print stylesheet
- PDF Typesetting
- Design that requires accurate output of physical dimensions
Notice:
- When displayed on the screen, the actual size of
pt
will be affected by the device resolution - Different operating systems may also have slightly different renderings of pt
What is pc
? Is it still commonly used now?
pc
(pick card) is also a printing unit, 1pc = 12pt. It is larger than pt
and is usually used in block-level units in typography.
Although it has a certain history in the printing industry, it is rarely used in web development. Although CSS supports pc
, most developers prefer to use pt
or px
because they are more intuitive and have better compatibility.
For example:
font-size: 1.5pc; /* is equivalent to 18pt */
Reasons for not recommended use:
- Poor readability, not as common as px or pt
- No obvious advantage to replace other units
- Mainstream frameworks and libraries basically do not use PC
Let's summarize the main differences:
unit | Full name | type | Main uses | Is it affected by the screen |
---|---|---|---|---|
px | Pixels | Digital units | Screen display, web page layout | yes |
pt | point | Printing unit | Print, PDF layout | No (theoretical) |
pc | Card | Printing unit | A few typesetting requirements | no |
Basically that's it. By understanding their usage scenarios, you can choose units reasonably in different projects.
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