Converting Em to Px in JavaScript (And Getting Default Font Size)

Converting em to px in Javascript (and getting default font size)

Edit: No, there isn't.

To get the rendered font size of a given element, without affecting the DOM:

parseFloat(getComputedStyle(parentElement).fontSize);

This is based off the answer to this question.

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Edit:

In IE, you would have to use parentElement.currentStyle["fontSize"], but this is not guaranteed to convert the size to px. So that's out.

Furthermore, this snippet won't get you the default font size of the element, but rather its actual font size, which is important if it has actually got a class and a style associated with it. In other words, if the element's font size is 2em, you'll get the number of pixels in 2 ems. Unless the font size is specified inline, you won't be able to get the conversion ratio right.

How can i get default font size in pixels by using JavaScript or JQuery?

There are a couple of situations this can be useful-

function getDefaultFontSize(pa){
 pa= pa || document.body;
 var who= document.createElement('div');

 who.style.cssText='display:inline-block; padding:0; line-height:1; position:absolute; visibility:hidden; font-size:1em';

 who.appendChild(document.createTextNode('M'));
 pa.appendChild(who);
 var fs= [who.offsetWidth, who.offsetHeight];
 pa.removeChild(who);
 return fs;
}

alert(getDefaultFontSize())

Dynamically convert em to px inside of css?

You don't need to convert units, calc can handle that:

calc(100% + 10px)
calc(2rem - 1%)
calc(var(some-var) + var(another-var))

https://developer.mozilla.org/en-US/docs/Web/CSS/calc

Change font-size in auto-generated HTML from px to em using javascript

If the styling is in HTML then it's inline styles. There's no CSS Wizardry that will override it. What you need to do is directly modify the inline styles.

Here's what you're looking for:

var elem = document.getElementById("elementID");
elem.setAttribute("style", "font-size: 2em");

You'll have problems in IE with setAttribute so if that's a concern ... you'll need to write a fallback to handle it.

Is sizing fonts using em still relevant?

Do not specify the font-size in absolute length units for screen stylesheets. They render inconsistently across platforms and can't be resized by the User Agent (e.g browser). Keep the usage of such units for styling on media with fixed and known physical properties (e.g print)

If you will use this method, no need to calculate

You can set the font-size of the body to 62.5%(that is 62.5% of the default of 16px), which equates to 10px, or 0.625EMs. Now you can set your font-size in EMs with an easy to remember conversion, divide the px by 10.

* 12px = 1.2EMs
* 13px = 1.3EMs
* 16px = 1.6EMs
* 8px = 0.8EMs
* etc…

This makes everything SUPER easy to remember and eliminates the need for conversion tables. Of course, you will still need to use a conversion table for nested elements when using EMs, if you are not being specific in your CSS, which is a whole separate issue.

But 76% is much better and you can use this to calculate http://pxtoem.com/

Yes it's still relevant:

IE6 is still widely used and is unable to resize the fonts defined in px. => Usability issues. That alone is a no-no.

and

IE 7 and 8 don't resize text sized with pixels either, actually. They do have page zoom, but some people prefer to incease text size only.

Here's a summary of what's good and bad about font sizing in general.

Font size in css http://easycaptures.com/fs/uploaded/213/2470522253.png

I personally like ems. Others, like Chris Coyier over at CSS-Tricks.com likes pixels. (Chris has an excellent article on the different font units).

It really comes down to personal preference.

Almost similar or related questions on SO

Should we still use em and % for defining the font-size of the website elements?

Is there really any point to using relative font sizing in CSS?

Why em instead of px?

Font size in CSS - % or em?

CSS font size: relative vs. absolute values. Which to use?

Problem with EM

Using relative instead of fixed size in CSS

Helpful online tool for px to em

http://pxtoem.com/

http://riddle.pl/emcalc/

http://convert-to.com/pixels-px-to-em-conversion.html

Convert entire site from px to em (This tool is still in development)

http://converter.elementagency.com/

EM Calculator AIR application (will work on all os)

http://jameswhittaker.com/journal/em-based-layouts-vertical-rhythm-calculator/

http://jameswhittaker.com/projects/apps/em-calculator-air-application/

Windows apps

http://www.thebrightlines.com/2009/11/16/pixem-pixel-to-em-converter/

http://www.storkas.com/Projects.aspx(go at bottom)

Pixels to Ems Conversion Table for CSS

http://jontangerine.com/silo/css/pixels-to-ems/

http://reeddesign.co.uk/test/points-pixels.html

emchart

http://aloestudios.com/tools/emchart/

http://aloestudios.com/code/emchart/

Some more articles on this issue

http://www.d.umn.edu/itss/support/Training/Online/webdesign/type.html

Why font-size in em's with important doesn't override font-size in px?

This answer is based on your posted fiddle in which:

.flex { 
    font-size: 50% !important;
}

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First of all, I should note that px is an absolute unit which unlike em, is not relative to the parent's font size. So it would be constant.

And in the demo you've provided, you'll get the value of font-size of the .child-em is pixels Because jQuery .css() method returns the computed style of elements.

From the jQuery doc:

.css( propertyName )
Get the computed style properties for the first element in the set of
matched elements.

In this particular case, you have change the font size of the parent to 50% of the default (which is 16px in most web browsers) by .flex class name, and then double that value again for the .child-em element by 2em.

Therefor the returned value would be 16px.

How to convert font size=10 to px?

<font size=1>- font size 1</font><br>
<span style="font-size:0.63em">- font size: 0.63em</span><br>

<font size=2>- font size 2</font><br>
<span style="font-size: 0.82em">- font size: 0.82em</span><br>

<font size=3>- font size 3</font><br>
<span style="font-size: 1.0em">- font size: 1.0em</span><br>

<font size=4>- font size 4</font><br>
<span style="font-size: 1.13em">- font size: 1.13em</span><br>

<font size=5>- font size 5</font><br>
<span style="font-size: 1.5em">- font size: 1.5em</span><br>

<font size=6>- font size 6</font><br>
<span style="font-size: 2em">- font size: 2em</span><br>

<font size=7>- font size 7</font><br>
<span style="font-size: 3em">- font size: 3em</span><br>

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