If you know anything about Search Engine Optimisation, you’re sure to be fairly familiar with the practice of “link building” (or link earning as it is more frequently becoming known as). The problem a lot of new SEO’s have when looking to build links isn’t that they don’t know how to physically build a link, they simply don’t know how to build a good link. The other problem SEO’s are now encountering is that building a link, let alone a good link, has become extremely hard to do.

Before we delve further into this, it’s worth checking out our blog on the difference between Follow and NoFollow links, as this article will focus on the former. In any case, I’ve taken a look at a range of the key link building metrics to consider when link building so that you have a clear understanding of what makes a good link, and why.

Domain Strength

Domain strength, (often referred to as Domain Authority), is the cumulative strength of an entire domain. Domain Strength is similar to PageRank, a system that Google used to use to score web pages from 0-10 based on number & quality of links pointing to a site in order to define that individual page’s overall strength. PageRank (named after one of the founders of Google, Larry Page) used to be updated every 3-4 months, however in late 2014 Google’s John Mueller stated in a Google Hangout that Google’s PageRank update of December 2013 was probably it’s last.

Many different SEO companies have attempted to put their own spin on the domain strength metric, with Moz perhaps coining the most well known version - Domain Authority. Domain Authority is a metric calculated by a Moz algorithm and runs on a scale of 1-100, with 100 being the highest possible score. Their tool uses a number of signals taken from their own crawler including;

  • linking root domains
  • total number of links
  • link popularity score
  • link trust

 

This is then calculated into a score which helps to approximate how competitive a particular site will be within in the search engines. It’s worth noting though that this is only one metric, and just because a site has a higher Domain Authority than another it doesn’t mean that it’s necessarily going to rank above it.

Ahrefs also have their own domain strength metric, going by the name of the Ahrefs Domain Rank. This metric ranks a page from 0-100 and measures the importance of a domain by verifying the number and the quality of it’s backlinks. A domain with a rank of 0-30 is generally considered unpopular, 31-70 meaning that it’s average, and 71-100 indicating that it’s very popular.

Whilst all of the above metrics that relate to domain strength have their own specific pro’s and cons, there is one key thing to remember. If we see one link as a vote from another website, the stronger/more authoritative the website voting for your site, the more that vote will be considered by the search engines. It is for this very reason that domain strength is one of the key metrics that should be considered when building links.

Page Strength

Page Strength, commonly known as Page Authority (again - another Moz naming convention) is another important link building metric to consider. This metric measures the strength of a single page rather than the strength of an entire domain.

Much like Moz’s Domain Authority, Page Authority is worked out on a score of 1-100 with 100 being the highest score that a page can achieve. The page with the highest Page Authority is typically the homepage as this page generally sees the most internal/external links back to it.

Besides Domain Authority, there are other companies including Majestic who have created their own page strength metric, which comes in the form of Citation Flow & Trust Flow. Citation Flow is a metric which is scored on how influential a URL on a site is. Citation Flow doesn’t consider the quality of links, so a high score is simply determined by the number of links pointing to that URL. Trust Flow is a metric which examines the volume of quality backlinks pointing back to a URL. If the sites/pages linking back to a site are deemed trustworthy, then the Trust Flow score is likely to be higher.

When using these two metrics, the main thing to look to consider is the ratio between them. Generally speaking, a good site would have a higher Trust Flow than Citation Flow. If this were the other way round, it could suggest that the site has a large quantity of low quality backlinks, and quality should always come before quantity in terms of off-page optimisation. This isn’t always necessarily the case though - as even Moz and Majestic have a lower Trust Flow than Citation Flow.

In link building terms, an ideal situation would be to get a link on a highly authoritative site on a particularly authoritative page.

The Number Of Outbound Links

When considering linking to a site, it’s extremely important to consider the number of links that are pointing away from a site. If you find a website with a high domain strength that doesn't have many links pointing away from it, it’s likely that any link you are able to get on that site will provide more value as the equity of the link will be shared between fewer websites. Having said that, it’s far harder to get a link on a website with only a small number of outbound links as these sites are typically far more cautious & stringent about who they link out to. However, as mentioned before, getting a link from a site with a high domain strength is likely to provide far more value to your site than a site with a large number of outbound links. The reason for this is simple. A site with a large number of outbound links has more sites to spread its authority across, therefore offering less value to each individual site.

Checking the number of links from a site also enables you to check the quality of those links. If there are spammy, low quality websites linking back to the site it may be worth avoiding as the site could be/could have been penalised. Should you go ahead & build the link, this penalty could have a direct affect on your sites visibility within the search engines.

Linking Root Domains

Linking root domains is the number of complete domains that link to a site, as opposed to the total number of single links. For example, if the BBC linked to your site from one news story, that would be one link and one linking root domain.

The number of linking root domains is a stronger signal than the complete number of links simply because it’s a far stronger indication of how popular a website is. Going back to the theory that each link is seen as a vote, each additional vote a website gives another has less value than the vote given previously. In any case, receiving multiple links from a single site is still worth its weight in gold, as your site would receive page authority & referral traffic.

Link Relevance

When link building, it’s vitally important that any site you consider trying to link to has a degree of relevance to the site you’re trying to link back to. A good link is a natural link as generally speaking, sites of a similar vein tend to link to each other

A great tool for looking into this is Majestic’s Topical Trust Flow. Topical Trust Flow is a tool which categorises links based on the topics of the sites they are linking to, providing a useful snapshot of a site’s topical relevance. To put this into context, using e-commerce fitness supplement store Myprotein as an example, it’s no real surprise to see that the top two topics are sports & strength sports, with food & shopping also in there.

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However, search engines could be suspicious of two sites that aren't in any way related linking to one another. The reason for this is connected to the relevance of a link. Why would a gardening website link to a children’s toy e commerce store? The two are fundamentally not related, so this link would be deemed less valuable than a link from a children’s welfare blog, for example.

Beyond link building, you are still looking to drive targeted traffic to your website so that you can attempt to convert your visitors into customers. For this reason alone, you should be trying to build links to websites where potential customers are likely to visit.

Social Strength

According to Google’s Matt Cutts, social signals do not influence rankings as of yet, however there have been various case studies to show that they do make a difference to SEO. It's long been muted by leading SEO's that social strength (activity on social, number of likes/follows/+1's, etc) does have an effect on SEO. Whilst public comments on the subject maintain this is correlation not causation, it’s still worth bearing in mind.

Social is also very effective for outreaching to potential link prospects. Additionally, if a potential linker has high social strength and they share your content, you're more likely to get RTs, exposure, and even links from that single share.

With this in mind, you should always try to communicate with profiles that have large social followings and are active on the social channels. In any case, it’s clear that whether or not it has a direct effect on SEO, social definitely makes a difference to a site's traffic & overall brand awareness.

Conclusion

Following these key link building metrics is a good starting point for those looking to improve the quality of the links they’re building. There is without doubt a range of other metrics that could be followed alongside these, but by following the ones listed above it’s likely that you are future proofing your link building (earning!) efforts.

It’s undeniable that link building has become an increasingly difficult skill to master, however what I believe is abundantly clear is that link building is no longer a way of tricking the search engines. It’s no longer a dark art in which you can magically make your website appear for unrelated phrases in the search engines. Link building is simply a marketing discipline in which you should try to promote your product, service or content in a place where the people you want to see it CAN see it. If you do this right you will have success in your link building efforts, and perhaps more importantly, success in your overall marketing efforts.