Responsive 3 Column Layout

CSS snippet for a fluid responsive 3 column layout.

1. 1/3 + 1/3 + 1/3
2. 1/2 + 1/4 + 1/4
3. 1/4 + 1/2 + 1/4
4. 1/4 + 1/4 + 1/2

<div class="col-one">

</div>

<div class="col-two">

</div>

<div class="col-three">

</div>

<div class="clear"></div>

.col-one, .col-two, .col-three {
    width: 30%;
    float: left;
    margin-right: 5%
}

.col-three {
    margin-right: 0;
}

.clear {
    clear: both;
}

@media screen and (max-width : 767px) {
    .col-one, .col-two, .col-three {
        width: 100%;
        float: none;
        margin: 0;
    }

    .col-one, .col-two {
        padding-bottom: 30px;
    }
}

<div class="col-one">

</div>

<div class="col-two">

</div>

<div class="col-three">

</div>

<div class="clear"></div>

.col-one {
	float: left;
	width: 48%;
	margin-right: 2%;
}

.col-two, .col-three {
	float: left;
	width: 24%;
	margin-right: 2%;
}			

.col-three {
	margin-right: 0;
}

.clear {
    clear: both;
}

@media screen and (max-width : 767px) {
    .col-one, .col-two, .col-three {
        width: 100%;
        float: none;
        margin: 0;
    }

    .col-one, .col-two {
        padding-bottom: 30px;
    }
}

<div class="col-one">

</div>

<div class="col-two">

</div>

<div class="col-three">

</div>

<div class="clear"></div>

.col-one, .col-three {
	float: left;
	width: 24%;
	margin-right: 2%;
}

.col-two {
	float: left;
	width: 48%;
	margin-right: 2%;
}			

.col-three {
	margin-right: 0;
}

.clear {
    clear: both;
}

@media screen and (max-width : 767px) {
    .col-one, .col-two, .col-three {
        width: 100%;
        float: none;
        margin: 0;
    }

    .col-one, .col-two {
        padding-bottom: 30px;
    }
}

<div class="col-one">

</div>

<div class="col-two">

</div>

<div class="col-three">

</div>

<div class="clear"></div>

.col-one, .col-two {
	float: left;
	width: 24%;
	margin-right: 2%;
}

.col-three {
	float: left;
	width: 48%;
	margin-right: 0;
}

.clear {
    clear: both;
}

@media screen and (max-width : 767px) {
    .col-left, .col-right {
        width: 100%;
        float: none;
    }

    .col-left {
        padding-bottom: 30px;
    }
}

Note

@media screen and (max-width : 767px) {

767px is the viewport width, i.e. the width of the screen or the browser viewport. 768px is the portrait width of iPad 2, so anything under that is mostly considered as mobile viewport, if you wish to make the responsive css trigger before, change 767px to something higher