I've been using px for almost all the measurement related styling, but I wanted to know the best places for the use of pixels (px), percentage (%), points (pt) and em.
I've seen the use of em and (I believe) points in typography, but I don't know the best way to use them.
Where should either be used, and why?
pt or cm, in, mm etc. are most used for print stylesheets, as they're most fit for measurements on the physical properties of paper sheets, and the render of printers.
em and en (and the new rem, and more interesting units such as ch) are glyph relative units, and as such are suitable for text styling, in correspondence with absolute units at the root element (e.g. px units at the body).
another interesting uses: ex units (the height of the 'x' glyph in the font) to set vertical measures in relation to text, ch to indent lines.
px are absolutely rendered so one can design a pixel-perfect (or fixed) layout based on these units, applied for containers, or on various widgets demanding fixed size (buttons and the like). disclaimer: absolutely is an over-statement, as pixels are rarely absolute, and has many factors affecting the rendered outcome - see this article about px as an angular measure.
% are mostly used in conjunction with an absolute unit at the top container, and are applied in various CSS techniques, such as the faux centered container. these units are also very handy for layouts that are fluid by nature. others, like the viewport relative vh, vw and vmin, may be used regardless of the parent's units.
all of the above is based on my personal views, as this subject is open for debate, and CSS techniques will keep evolve and we'll see more uses of the specifications and capabilities we had never thought of. it's mostly the creative use of those tools that scopes or favors the use of one unit over another.
It used to be that these distinctions mattered: for example, back in the IE6 days, you should never set your text using px, because then it couldn't be zoomed. That is, back in the day, browsers actually treated px as a number of pixels.
These days, browsers have conformed to web reality: most people use px everywhere, for almost everything. Thus px is now defined as an angular measurement, which essentially means that px behaves just fine in any zoom setting and on any size or DPI device.
Similarly, as part of conforming to web reality, all other units are defined in terms of px, so there is really no reason to use them unless it happens to be more convenient for your case. The only exception is, of course, percentages, since they allow you to specify values in relation to parents' measurements.
Details from the spec:
in, cm, mm, pt, and pc are all defined relative to px, since in practice all devices follow "For a CSS device, these dimensions are ... anchored ... (ii) by relating the pixel unit to the reference pixel." And as discussed, the "reference pixel" is an angular measurement that varies depending on DPI settings, screen size, zoom level, device type and so on.
1em equals the computed font-size of an element, which is usually defined in px. If that size itself is defined in ems or exs, the browser then looks upward until it finds a px to be relative to, eventually falling back to the default font-size (usually 12px).
1ex equals the height of the letter "x" in the defined font-size if possible, but usually (?) falls back to 0.5em.
Use px for elements that are of a set size.
Use percentage when you need the element to be in proportion to the window size or parent element size.
em is the standard for text, it adjust according to screen size on a mac. Make it a habit, there's plenty of good blogs on why to use em, em is not just for font properties it also comes in handy with other elements like div, inputs etc. There may be consequences when using px for font size, there's also situations where px and % will be more ideal, it' takes trial & error to understand fully.
There are no real rule on what to use it's all according to the desired effect. As you create you will test your site in different resolutions and adjust the browser size to see how it appears from a variety of users points of view.
Consider cross browser compatibility & resolution with em,
Consider resolution with percentages,
Disclosure: I am a sysadmin, not a web designer.
I generally use em for padding around images, so as to keep the padding sized according to the text it keeps away from the image.
I use % to handle liquid/fluid layouts sometimes, though most often a fluid layout will just be 100% of the browser but with fixed width (px) columns.
I use px to handle column widths, headers, etc. The height and width attributes of an <img> tag are of course in pixels by default, and an image will render best if you don't ask the browser to resize it from its native/original resolution. In some cases, you need to use px on fonts, when the font has to work with an image (i.e. a spanner icon next to the word "Tools"). If possible, I always use UTF-8 fonts instead of images.
Related
There's quite a lot of resources encouraging to use ems over pixels in media queries. However, none of them easily explains the obvious doubt about it:
If I have two divs and I want to hide one of them on iPhone4-like devices, how do I do it with em-based media queries? The device resolution is 640x960 in pixels.
In every article there a note that usually 1em = 16px. But since it is not certain, why would I want to convert to ems and risk breaking my design? What if user changes his default font to 20px? Or 10px? My div will hide either too soon or too late.
Example from Foundation:
/* min-width 641px, medium screens */
#media only screen and (min-width: 40.063em) { }
How can I be sure it really is 641px and not 1282px? Why would anyone use something so untrustworthy instead of old good pixels?
First the sizing in em cannot be changed by the user as this is a browser setting that cannot be changed. So at best it could vary between browsers but I don't know any that differs from this standard. For that reason, it can be considered quite safe to use.
But for media queries, I would recommend to use rem units. em units is mostly preferred for font sizing in components as it scales relatively based on the parent DOM element. While rem units work well for sizing root elements (width, height...).
px is an absolute unit of measurement (like in, pt, or cm) that also
happens to be 1/96 of an in unit. Because it is
an absolute measurement, it may be used any time you want to define
something to be a particular size, rather than being proportional to
something else like the size of the browser window or the font size.
em is not an absolute unit - it is a unit that is relative to the
currently chosen font size. Unless you have overridden font style by
setting your font size with an absolute unit (such as px or pt), this
will be affected by the choice of fonts in the user's browser or OS
if they have made one, so it does not make sense to use em as a
general unit of length except where you specifically want it to scale
as the font size scales.
Based on this, the most accurate option is using px instead of embased on what you are asking, but you can always redefine your fonts and use rem instead, this is better for responsive websites, together with percentages. That's a matter of judgment in every single element you are adding to your website, and of course, lots of testing to make sure it looks good and works flawless on any resolution and devices.
I personally prefer to do it this way:
I define my fonts and font-sizes (this overrides the default ones)
I use percentages for the block elements
I use rem for the fonts and media queries
But of course sometimes I have to use pixels or change some of my "default" rules depending on my needs. As I said before, it's too a matter of judgement on your needs and on it is best.
Note: The em unit is relative to the font-size of the parent. The rem unit is relative to the root—or the html—element. That means that we can define a single font size on the html element and define all rem units to be a percentage of that.
I'm building a responsive website and I'm wondering what unit I should use? I've seen a lot of sites using pixels (px) for measurements and I've seen some using percent (%). Is there a preferred — or right — way of doing responsive design?
I've found percent to be hard to use, since it makes calculations hard and I've ended up with values like 2.754% and so on when setting widths/margins etc. Pixels seems easier, it's just simple addition and subtraction, but I've read that it isn't "future proof" or something like that and wont scale properly if the user zooms in the browser window. Is that still true?
If you have any experience or expertise, please share! I would love to hear what you guys have to say!
Thanks!
For layout type things like the sizes of boxes, you want to use % because you will typically have several columns sized as a percentage of their parent that will stack on top of each other at a certain breakpoint (width:100%). No other unit will allow you to fill 100% of the space like % does.
For padding/margins use em, normally you will want to space your elements out relative to the size of your text. With em (the with of an 'M' character) you can quite easily say I want approximately 1 character spacing here.
For borders you can use px or em, there is a difference though. If you want your border to look like it's one pixel wide on all devices, use 1px. It may not be one pixel on all devices however, high density displays convert 1px into 2px for example. If you want your border to be a size based on your font, use em.
For fonts use em (or %), the use of em carries through parents to children and it just a nicer unit to work with over px.
Of course you must use percentage. But with the min-height, max-height, min-width, max-width CSS keys.
For the next generation
vw and vh. The vw is 1/100th of the window's width and the vh is 1/100th of the window's height.
For responsiveness they are going to be the new units.
Use percentages along with min-width and max-width in pixels. This stops percentages making your divs too small or too large. eg
div {
width:100%; //full width of browser
max-width: 960px; //this means it will be 100% of the browser until 960px then it will stop expanding
}
For layouts vh and vw are good because they are relative to the device's view port. They give you the possibility of designing with the view port of the device in mind. With this said you know what will show on the window and what won't without being too careful.
For text em is best because if it's responsive features.
This question already has answers here:
What is the difference between px, em and ex?
(4 answers)
Closed 1 year ago.
What is the difference between px and em?
Meet the Units
“Ems” (em): The “em” is a scalable unit that is used in web document
media. An em is equal to the current font-size, for instance, if the
font-size of the document is 12pt, 1em is equal to 12pt. Ems are
scalable in nature, so 2em would equal 24pt, .5em would equal 6pt,
etc. Ems are becoming increasingly popular in web documents due to
scalability and their mobile-device-friendly nature.
Pixels (px): Pixels are fixed-size units that are used in screen
media (i.e. to be read on the computer screen). One pixel is equal
to one dot on the computer screen (the smallest division of your
screen’s resolution). Many web designers use pixel units in web
documents in order to produce a pixel-perfect representation of
their site as it is rendered in the browser. One problem with the
pixel unit is that it does not scale upward for visually-impaired
readers or downward to fit mobile devices.
Points (pt): Points are traditionally used in print media (anything
that is to be printed on paper, etc.). One point is equal to 1/72 of
an inch. Points are much like pixels, in that they are fixed-size
units and cannot scale in size.
Percent (%): The percent unit is much like the “em” unit, save for a
few fundamental differences. First and foremost, the current
font-size is equal to 100% (i.e. 12pt = 100%). While using the
percent unit, your text remains fully scalable for mobile devices
and for accessibility.
So, What’s the Difference?
It’s easy to understand the difference between font-size units when you see them in action. Generally, 1em = 12pt = 16px = 100%. When using these font-sizes, let’s see what happens when you increase the base font size (using the body CSS selector) from 100% to 120%
As you can see, both the em and percent units get larger as the base font-size increases, but pixels and points do not. It can be easy to set an absolute size for your text, but it’s much easier on your visitors to use scalable text that can display on any device or any machine. For this reason, the em and percent units are preferred for web document text.
Em vs. Percent
We’ve decided that point and pixel units are not necessarily best suited for web documents, which leaves us with the em and percent units. In theory, both the em and the percent units are identical, but in application, they actually have a few minor differences that are important to consider.
In the example above, we used the percent unit as our base font-size (on the body tag). If you change your base font-size from percent to ems (i.e. body { font-size: 1em; }), you probably won’t notice a difference. Let’s see what happens when “1em” is our body font-size, and when the client alters the “Text Size” setting of their browser (this is available in some browsers, such as Internet Explorer).
When the client’s browser text size is set to “medium,” there is no difference between ems and percent. When the setting is altered, however, the difference is quite large. On the “Smallest” setting, ems are much smaller than percent, and when on the “Largest” setting, it’s quite the opposite, with ems displaying much larger than percent. While some could argue that the em units are scaling as they are truly intended, in practical application, the em text scales too abruptly, with the smallest text becoming hardly legible on some client machines.
Info taken from http://kyleschaeffer.com
1 em = take font size from your Document font-size. It is relative in nature.
100% = take size also from document font size.
General
12pt=1em=100%=16px
In Best Practise Use % because it is relative to your width, it will automatic adjust device to device.
As you know, you can specify dimensions with CSS in px or em. As far as I understand it, em means "line height of the current element's fonts". My approach currently is to always use px (also for margin which seems to be a controversial practice).
Question: Can I rely on the ratio of px and em to be the same across browsers? If not, then my manually specified margins between paragraphs will likely look odd because they so not match 1em anymore.
I believe that it is better to use em for margins but I have quite a base of existing code that always uses px margins.
No. ems are relative to the user's chosen font size, px aren't. The default font sizes of desktop browsers are about the same in pixels, but mobile devices in particular will vary even before user adjustment.
You should use em for a margin in text content that should be sized similarly to the surrounding fonts, and px for a margin that has to line up with images used by the page layout.
No, you cannot.
The size of em in pixels is related to the font type & size you're using, the resolution of your screen (depending on OS, browser), and possible further OS and browser settings - eg "Show fonts +10%" may alter the em value.
I have designed and developed more than 10 sites, but I still have a doubt about the correct unit I should use. Should it be px, em or %?
EDIT 1: FOR LAYOUTS (Especially for container boxes)
Different units depending on context. If there was one that was best for every situation, then there wouldn't be so many units.
As rules of thumb go:
If you are working on screen media:
Use % for font sizes
Use px for images
Use px, %, or em for box sizes
Use ratios for line height
If you are working in print media:
It might be wise to avoid px (this is not a hard rule by any means) and everything else is fair game. It really depends how much control you want.
There's no real right or wrong, but as a rule of thumb:
For anything you want a certain, fixed size, use PX
For anything you want to scale with font-size, use EM
For anything you want to scale to the available space in the window/container, use %
Each used to have specific advantages or disadvantages in different browsers when it came to users scaling the browser's base font-size/zooming, but more recent versions of the browsers by-and-large get around these issues by scaling everything, not just font-size.
If you're talking about font-size then px and pt are not ideal.
Ems and Percent units are scalable, therefore they are far more accessible - friendly for the visually-impaired. They also scale down well for mobile phone users.
Px and Pt units do not scale upward for visually-impaired users, or downward for mobile phones.
If you're talking about layout or containers then it depends on the type of design you want - fluid or static - and there isn't necessarily a "right" answer.
Without going into an example, it's difficult to advice. Do you have a site in mind we could look at?
Use the unit you need in the specific context.
Unit Description
====================
% percentage
in inch
cm centimeter
mm millimeter
em 1em is equal to the current font size. 2em means 2 times the size of the current font. E.g., if an element is displayed with a font of 12 pt, then '2em' is 24 pt. The 'em' is a very useful unit in CSS, since it can adapt automatically to the font that the reader uses
ex one ex is the x-height of a font (x-height is usually about half the font-size)
pt point (1 pt is the same as 1/72 inch)
pc pica (1 pc is the same as 12 points)
px pixels (a dot on the computer screen)
source: http://www.w3schools.com/css/css_units.asp
For flexibility and accessibility I recommend using % for horizontal measures (relative to the user's screen), and em for vertical measures (relative to the user's font setting).
For fixed width layouts
For as much as pixel perfection I would suggest to use PX for width ,height, margin, and padding
for line-height use unit-less value like {line-height:1.2}
for typographic elemets use {font-size:62.5%) for body then use em for other elements
in HTML for <img> always use unit-less width and height .