PageRank is an algorithm designed by Google to help assess the authority of a Web page and website overall (1). One of several quality metrics Google uses to determine the authority of a website, PageRank assigns a score between 0 and 10 to a website to determine its relative value to users.
Google wants to give users the most relevant and quality information available, so it may place pages with bigger PageRank scores higher up in the search engine results pages. Even though PageRank is only one of several signals that determine how well a page performs in search results, you need to understand how Google assigns this score and the role it plays in your optimization efforts.
When another website embeds a link that points to your Web page, Google sees this as endorsement of the content on your page. The search engine analyzes websites pointing to your page and assesses the quality of each based on their domain authority. It then uses this information to decide the significance of your individual Web pages and your website overall.
When a website links to your page, or you link your internal pages together, the linking page gives PageRank value to the page it is linking to. This transfer of PageRank value is commonly referred to as link juice.
The quantity of link juice that passes from one page to another depends on the PageRank of the page where the link originates and the number of links on the page transferring PageRank (1). Even though every website has a PR score between 0 and 10, the value that a Web page gets from links that come from authoritative websites frequently surpass 10.
Every Web page has a finite amount of link juice it can offer to other pages. That limit is determined by the total PageRank value the linking page has itself. If Page A has a PageRank of 15, it cannot transfer more than 15 total link juice points to other sources. If Page A links to only one other page, Page B, then Page B will get all 15 of those link juice points. If Page A links to three pages, B, C and D, then those pages will get a link juice value of 5 each. Every passing link has a decay factor, so a little more link juice is lost with every transfer, but the easiest way to understand PageRank is by dividing the total points a page has by the number of links on the page. This will give you a rough idea of how much link juice is given to each corresponding page.
If you have a page with high a PageRank and you need to link to several pages that are less important for ranking, you may wish to prevent link juice from passing to them. One example of this is when your product page links to the terms and conditions page, or even the shopping cart. These pages are important for the user experience, but you certainly don't need your shopping cart to rank in search engine results pages. You have the option of putting commands into your on-page code that tells search engine crawlers to ignore the link on the page. This is called a rel=nofollow tag.
If you have a page that links to three others, and you put rel=nofollow on one of those links, that link will not be followed by search engine spiders and consequently will not pass along link juice. It's important to note, though, that many SEO practitioners claim that preventing the transfer of link juice to a page does not conserve it. On the contrary, many SEO professionals advise against preventing PageRank from passing naturally through the pages on your site.
PageRank transfer can tell search engines what your pages are about and how important they are. For instance, if you have a page that houses a customer acquisition tool and you write a blog entry that talks about how to find new customers, you could link to your tool from descriptive or anchor text in your blog post. Often called siloing, this internal linking strategy helps search engines understand the main content of your website and which pages are most important.
It's important to understand that linking strategies should be approached with caution. Google's ability to evaluate the quality and source of links has gotten vastly more sophisticated over the years, and links from spam-ridden websites can actually hurt your SEO efforts rather than help them. Many websites are now suffering ranking declines and other penalties because of low-quality links pointing at their pages.
When it comes to getting links pointing at your website, your job is to focus on quality, not quantity. Quality websites with good domain authority are great link prospects, including highly trusted sites like government and university institutions. The best way to get PageRank passed on to your important pages is to develop relationships with owners and administrators of these high-quality sites. Help them share their content with appropriate audiences, and show them how your content will also help their fans and followers.
Understanding how PageRank works is the first step toward success with SEO. The second step is to find valuable sites that can help you achieve your goals and prove you are worthy of being a part of their own linking strategy.