How to center an iframe horizontally?

best way and more simple to center an iframe on your webpage is :

<p align="center"><iframe src="http://www.google.com/" width=500 height="500"></iframe></p>

where width and height will be the size of your iframe in your html page.

Add display:block; to your iframe css.

div, iframe {
    width: 100px;
    height: 50px;
    margin: 0 auto;
    background-color: #777;
}

iframe {
    display: block;
    border-style:none;
}

<div>div</div>
<iframe src="data:,iframe"></iframe>