Centering a div block without the width

I have a problem when I try to center the div block "products" because I don't know in advance the div width. Anybody have a solution?

Update: The problem I have is I don't know how many products I'll display, I can have 1, 2 or 3 products, I can center them if it was a fixed number as I'd know the width of the parent div, I just don't know how to do it when the content is dynamic.

.product_container {
  text-align: center;
  height: 150px;
}

.products {
  height: 140px;
  text-align: center;
  margin: 0 auto;
  clear: ccc both; 
}
.price {
  margin: 6px 2px;
  width: 137px;
  color: #666;
  font-size: 14pt;
  font-style: normal;
  border: 1px solid #CCC;
  background-color:	#EFEFEF;
}

<div class="product_container">
  <div class="products" id="products">
    <div id="product_15">
      <img src="/images/ecommerce/card_default.png">
      <div class="price">R$ 0,01</div>
    </div>

    <div id="product_15">
      <img src="/images/ecommerce/card_default.png">
      <div class="price">R$ 0,01</div>
    </div>   

    <div id="product_15">
      <img src="/images/ecommerce/card_default.png">
      <div class="price">R$ 0,01</div>
    </div>
  </div>
</div>

Update 27 Feb 2015: My original answer keeps getting voted up, but now I normally use @bobince's approach instead.

.child { /* This is the item to center... */
  display: inline-block;
}
.parent { /* ...and this is its parent container. */
  text-align: center;
}

My original post for historical purposes:

You might want to try this approach.

<div class="product_container">
    <div class="outer-center">
        <div class="product inner-center">
        </div>
    </div>
    <div class="clear"/>
</div>

Here's the matching style:

.outer-center {
    float: right;
    right: 50%;
    position: relative;
}
.inner-center {
    float: right;
    right: -50%;
    position: relative;
}
.clear {
    clear: both;
}

JSFiddle

The idea here is that you contain the content you want to center in two divs, an outer one and an inner one. You float both divs so that their widths automatically shrink to fit your content. Next, you relatively position the outer div with it's right edge in the center of the container. Lastly, you relatively position the inner div the opposite direction by half of its own width (actually the outer div's width, but they are the same). Ultimately that centers the content in whatever container it's in.

You may need that empty div at the end if you depend on your "product" content to size the height for the "product_container".

An element with ‘display: block’ (as div is by default) has a width determined by the width of its container. You can't make a block's width dependent on the width of its contents (shrink-to-fit).

(Except for blocks that are ‘float: left/right’ in CSS 2.1, but that's no use for centering.)

You could set the ‘display’ property to ‘inline-block’ to turn a block into a shrink-to-fit object that can be controlled by its parent's text-align property, but browser support is spotty. You can mostly get away with it by using hacks (eg. see -moz-inline-stack) if you want to go that way.

The other way to go is tables. This can be necessary when you have columns whose width really can't be known in advance. I can't really tell what you're trying to do from the example code — there's nothing obvious in there that would need a shrink-to-fit block — but a list of products could possibly be considered tabular.

[PS. never use ‘pt’ for font sizes on the web. ‘px’ is more reliable if you really need fixed size text, otherwise relative units like ‘%’ are better. And “clear: ccc both” — a typo?]

.center{
   text-align:center; 
}

.center > div{ /* N.B. child combinators don't work in IE6 or less */
   display:inline-block;
}

JSFiddle

Most browsers support the display: table; CSS rule. This is a good trick to center a div in a container without adding extra HTML nor applying constraining styles to the container (like text-align: center; which would center all other inline content in the container), while keeping dynamic width for the contained div:

HTML:

<div class="container">
  <div class="centered">This content is centered</div>
</div>

CSS:

.centered { display: table; margin: 0 auto; }

.container {
  background-color: green;
}
.centered {
  display: table;
  margin: 0 auto;
  background-color: red;
}

<div class="container">
  <div class="centered">This content is centered</div>
</div>

Update (2015-03-09):

The proper way to do this today is actually to use flexbox rules. Browser support is a little bit more restricted (CSS table support vs flexbox support) but this method also allows many other things, and is a dedicated CSS rule for this type of behavior:

HTML:

<div class="container">
  <div class="centered">This content is centered</div>
</div>

CSS:

.container {
  display: flex;
  flex-direction: column; /* put this if you want to stack elements vertically */
}
.centered { margin: 0 auto; }

.container {
  display: flex;
  flex-direction: column; /* put this if you want to stack elements vertically */
  background-color: green;
}
.centered {
  margin: 0 auto;
  background-color: red;
}

<div class="container">
  <div class="centered">This content is centered</div>
</div>