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Backlinks vs. Referring Domains: What’s the Difference?

Are you considering building links to your website?  If so, you’ve probably come across the terms “backlinks” and “referring domains.” Sometimes, they can appear to be used interchangeably, but they’re quite different and it’s important to understand their relationship. 

One of the first things we as an SEO team look at when we analyze a new client’s link profile is the number of referring domains (RDs)–that is, the number of unique websites that link to theirs. 

Backlinks (BLs), on the other hand, refer to the actual number of links being sent to their site. It isn’t uncommon for a single RD to direct more than one backlink to their site, which is why the number of backlinks will always exceed the number of referring domains for any given website. 

Backlinks vs. Referring Domains: Which one matters more?

The answer is referring domains. Sometimes a client’s site has only a handful of RDs but thousands of BLs. This typically happens when a small number of RDs send a disproportionate number of links to their site, which can be an indicator of spammy link building tactics. 

Take a look at this website, for example:

It’s unlikely that each of the 797 referring domains is generating an equal number of links. 

In fact, nearly half of the BLs originate from just one RD–giantfishing.co.kr–and closer review will show that the BLs are of low quality. While a large number of BLs sounds ideal, it has the opposite effect in excess. Many RDs that link to a website thousands of times have embedded a target URL in multiple locations–in sidebars, footers, and even headers that appear on every one of their pages. Google devalues these kinds of links and, if it sees a trend emerging in your backlink profile, the search engine will take harsh steps to make sure you’re not gaming the algorithm–typically by hitting you with a Manual Action penalty.

In Google’s eyes, a high number of RDs is more valuable than a lot of BLs, since it infers that a large number of domains find your website useful and credible. Think of it this way: If you owned an ice cream store, would you rather have 100 unique customers recommend your business to each of their friends, or a single customer tell their best friend “this ice cream rocks!” 100 times? 

The greater the number of unique, authoritative sources that share an opinion about a website, the more reliable it’s considered to be.

As with the ice cream shop analogy, it’s better to have 100 unique RDs linking to your website than one referring domain linking to you 100 times. This is how Google assigns greater authority and trustworthiness to a website.

BL to RD ratio

The backlink to referring domain ratio gives us the average number of links the domain sends to a site: 

BL:DR ratio =  (# of backlinks) / (# of referring domains)

Ideally, the best BL to RD ratio is 1:1. Realistically, it’s extremely rare to find a site with a 1:1 ratio, but the closer you can get, the better. In the case of giantfishing.co.kr that we looked at above, the ratio is 34:1. Although we’ve seen sites with ratios as high as 1000:1, 34:1 is still pretty high. It’s ideal to have the BL value in the single digits.  

The key takeaway is that once you acquire a link from a domain, additional links from the same RD have diminishing returns. Each additional link dilutes the “link juice” to your website, so it’s best to move on and pursue BLs from other sites. 

Can you have too many backlinks?

There’s no such thing as having too many high-quality backlinks. However, if you have a large number of backlinks from only a handful of referring domains, it’s a good idea to review them manually. If you think they could be harmful, disavow the links (with the disavow feature, you can request that Google ignore those links). Be sure to speak with an SEO professional before doing so since disavowing the wrong links or too many of them can be as or more harmful.

In the earliest days of search, link building manipulation was an effective way to boost organic rankings. Webmasters built or even paid for relationships with a handful of websites to create and direct tons of BLs back and forth. 

Once Google caught on to the manipulation, it launched (in 2012) what became known as the Penguin algorithm update to devalue sites that were engaging in link building schemes. Many sites were rightfully penalized by the update, and the algorithm has become increasingly sophisticated to detect and quash new schemes. That’s why building editorial links with high quality sites is the best, and safest, way to enhance your website’s link profile.  

Is it possible to have too many referring domains?

The number of referring domains depends on their quality. A large number of low quality RDs is a surefire way to put your site at risk of a manual action penalty from Google since they can be interpreted as link spam.

On the other hand, Google looks at a large number of high quality RDs as a signal of an authoritative website. Acquiring a high number of quality backlinks takes time and effort, but it pays high SEO dividends in the long term. 

Final Thoughts

Website backlinks and referring domains tell us a lot about the strength of a link profile. Take the time to understand their relationship and develop an effective link building strategy.