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Using css3 calc in an attribute value to compute its value at runtime


The CSS calc value in css is rel­a­tively new but pretty powerful.The calc value lets you do two impor­tant things

  • Per­form com­pu­ta­tion across units.
  • Com­pute dimen­tions at runtime.

The calc attribute value can be used any­where a length, frequency, angle, time, number, or integer value is required.

Before you adopt it in your appli­ca­tion, make sure its browser com­pat­i­bil­ity matches your busi­ness requirements.

Basic exam­ple

Con­sider the fol­low­ing snippet

<div class="outer">
  <div class="inner"></div>

And the fol­low­ing snip­pet of CSS

.outer {
  width: 500px;
  height: 100px;
  background: #dadada;

.inner {
  width: calc(100% - 40px);
  height: 50px;
  margin: auto;
  border: 1px solid blue;

Instead of spec­i­fy­ing width directly, we can now com­pute the width on the fly depend­ing upon the ren­dered width of the par­ent. Ther­fore in this case, the inner div has a width which is 40px less than width of the outer div. And we were able to neatly cen­ter align it using a mar­gin of auto.

Here’s the Jsfid­dle of the above code.

Cre­at­ing a chrono­log­i­cal timeline

I have always wanted to cre­ate a time­line with con­nec­tors. Until now, this wasnt pos­si­ble with­out doing hacks. But the new calc prop­erty makes is so much simpler.

Con­sider this html structure

<div class="chronology">
    <div class="event">
        <div class="connector"></div>
        <div class="event-details">
            <div class="col-1">
                <div class="baloon">1965</div>
            <div class="col-2">
                <div class="headline">Touch screen technology was invented by E.A. Johnson</div>

Our chronol­ogy con­tainer can con­tain sev­eral chrono­log­i­cal events. Each event has a con­nec­tor, and two columns. The first colum holds the bal­lon with the date of the event and the sec­ond col­umn holds the descrip­tion of the event.

Here’s the css that will make this work

.chronology {
    margin: 20px;
.event {
    float: left;
    position: relative;
    padding-bottom: 20px;
.baloon {
    border-radius: 50%;
    color: #768696;
    height: 42px;
    width: 42px;
    text-align: center;
    font-size: 15px;
    margin: 0 30px;
    line-height: 2.6em;
    font-weight: bold;
    border: 2px solid #8A97ED;
    box-sizing: border-box;
.connector {
    position: absolute;
    left: 51px;
    top: 42px;
    width: 2px;
    height: calc(100% - 42px);
    background-color: #8A97ED;
.event-details {
    display: block;
[class|="col"] {
    box-sizing: border-box;
    float: left;
    margin-left: 0;
.col-2 {
    width: 270px;
    position: relative;
.headline {
    width: 250px;

The most impor­tant thing in this exam­ple was the con­nec­tor. We needed to sub­tract the height of the baloon from the con­nec­tor and posi­tion it at just below the baloon so that it extends till the end of the par­ent event.

Check out this Jsfid­dle Demo for the above code.

For the curi­ous among you, here’s the full list of the events that I was try­ing to map into this visualization.

Ryan Sukale

Ryan is just a regular guy next door trying to manage his life and finances.