Backlink

What Google says about backlinks

Google's own documentation is short on this point: "Google uses links as a signal when determining the relevancy of pages and to find new pages to crawl" (Link best practices for Google). A backlink does two jobs, then: it helps Google find your page, and it counts as one of the signals of what the page is about and how much it matters.

The same signal is why Google treats manipulation as spam. Its spam policies define link spam as "the practice of creating links to or from a site primarily for the purpose of manipulating search rankings", and the first example listed is "buying or selling links for ranking purposes" (Spam policies for Google web search). Swapping links excessively, links required by a contract and automated link building are on the same list. A backlink helps when it is a genuine reference; a paid or traded one that passes ranking credit breaks the rules.

Followed, nofollow, sponsored and ugc

A plain link, with no rel attribute, is what SEOs call a dofollow link. Google asks site owners to mark paid placements with rel="sponsored", links in comments and forum posts with rel="ugc", and to use rel="nofollow" when neither applies and they would rather not be associated with the linked page (Qualify your outbound links to Google).

Since September 2019, Google has said that all three attributes "are treated as hints about which links to consider or exclude within Search", rather than strict instructions (Evolving nofollow, Google Search Central blog). Each one is explained under nofollow link, with rel="sponsored" and rel="ugc" in their own section.

What studies of millions of pages show

Most pages have none. In Backlinko's analysis of 11.8 million Google results, approximately 95% of all pages had zero backlinks, and the #1 result had on average 3.8 times more backlinks than the results in positions 2 to 10.

Pages at the top have links from many more sites. According to Semrush's ranking factors study, pages ranking #1 have more than 200 referring domains on average, against fewer than 80 for pages at #10.

Without any, search traffic is rare. In Ahrefs' study of its index, 96.55% of pages get no traffic from Google, and among pages with no referring domains only about 1 in 6,671 gets more than 1,000 search visits a month.

These are correlations measured with the tools' own link indexes, not Google's data. They show that links and rankings go together; they do not show that one more link moves one page by a given amount. More sourced figures are on the statistics page.

Backlinks versus referring domains

A backlink count adds up every link; a referring domain count adds up the sites they come from. Fifty links from one site's footer show up as fifty backlinks and one referring domain. Most SEO tools report both, and the number of referring domains usually tells you more, because each new site is a separate decision to link.

The ratio between the two is worth a look in an audit. A sudden jump in backlinks with almost no new referring domains usually means one site added a sitewide link, in a footer or a blogroll, rather than many sites citing you.

Backlinks and outbound links

An outbound (or external) link is the same link seen from the other end: a link on your page that points to another site. Your outbound link is the other site's backlink. Linking out to the sources you rely on is a normal part of writing for the web, and on a page that cites studies it is what lets readers check them.

Google's guidance on outbound links is about qualifying the ones that are not plain editorial references: rel="sponsored" for paid and affiliate links, rel="ugc" for links in comments and forum posts, and rel="nofollow" when you would rather not be associated with the page you link to (Qualify your outbound links to Google). Selling followed links from your pages is the other side of the link spam Google's policies describe.

What makes one backlink worth more than another

A contextual link in the body of a relevant, visited page carries more weight than a link in a footer, a sidebar or a comment on an unrelated blog. Relevance between the two pages, the linking page's own authority and traffic, and the anchor text all play a part; the full list is in what makes a good backlink.

Quality beats quantity. A handful of links from respected sites in your field usually outweighs hundreds of weak ones, and networks built to sell links, such as a private blog network, can lead to a manual action rather than a boost.

How to see your own backlinks

Google Search Console's Links report shows your most linked pages, the sites that link to you most and the most common link text, for free (Links report, Search Console Help). Google notes that it is a sample rather than every link, that it can list links which have since been removed, and that it does not say whether a link is nofollow.

To check one link in particular, whether it is still live, followed and on a page Google can index, use the free link checker. For the paid crawlers that map a whole link profile, see the best backlink and SEO tools.