What is outbound link ratio?
Outbound link ratio compares how many sites a website links out to with how many sites link to it. A site that 400 domains link to, and that links out to 6,000 domains, has an outbound link ratio of 15 to 1: for every site that vouches for it, it vouches for fifteen others.
The term is not standardized, and SEOs use it in two ways:
- Domain level: linked domains (unique sites the domain links to) divided by referring domains (unique sites linking to the domain). This is the version used in site vetting.
- Page level: the number of external links on a single page, compared with its total links or its length. A 600-word article with 12 external links to unrelated businesses has a high page-level ratio.
Outbound links are the links a page sends out, while backlinks are the links other pages send in [1]. The ratio puts the two side by side.
Why does outbound link ratio matter?
Outbound link ratio matters because sites that sell or trade links link out far more than they are linked to. A real publication earns links from other sites as it publishes, so its linked domains and referring domains tend to grow together. A site that exists to place links keeps adding outbound links to new destinations with every post, while few sites have any reason to link back.
Search Insider uses outbound link ratio as one of its checks when vetting a site, because it is hard to fake. A site can inflate authority metrics or buy traffic, but every paid placement adds to its linked domains, and the ratio keeps the record.
Google cares about the outbound side too. Its manual actions include one for "unnatural links from your site," issued when Google detects "a pattern of unnatural artificial, deceptive, or manipulative outbound links on your site" [4]. Selling links that pass ranking credit is link spam under Google's policies [5]. In 2009, Matt Cutts of Google wrote that "Google trusts sites less when they link to spammy sites or bad neighborhoods" [3].
How do you calculate outbound link ratio?
To calculate outbound link ratio, divide the number of unique domains a site links to by the number of unique domains linking to it. Most backlink tools report both numbers on a domain overview, as "linked domains" and "referring domains."
Outbound link ratio = linked domains ÷ referring domains
Example: 3,200 linked domains ÷ 800 referring domains = 4For the page-level version, open a recent article, count the external links in the body text, and note how many point to commercial pages unrelated to the article's topic. Repeat across five to ten recent posts, because one heavily referenced article proves nothing.
What is a good outbound link ratio?
There is no published good outbound link ratio. Google has never released a ratio or threshold, and Search Insider has found no study that ties a specific number to penalties or lost rankings. Google's own guidance on links per page is deliberately vague: "There's no magical ideal number of links a given page should contain. However, if you think it's too much, then it probably is" [6].
What the ratio gives you is a comparison, not a pass mark. Read it this way:
| What you see | What it usually means |
|---|---|
| Linked and referring domains of similar size | A normal site that cites sources and gets cited back |
| Linked domains several times referring domains, links mostly to sources and references | A reference-heavy site such as a news aggregator or resource directory; check the type of site |
| Linked domains many times referring domains, links mostly to unrelated businesses in article bodies | The pattern of a site that sells placements |
| Linked domains growing sharply month on month while referring domains stay flat | Placements being added at volume |
The numbers in any example are illustrations. The type of site always changes the reading: a news site that links to many sources and a link seller that links to many clients can have similar ratios, and only looking at the links tells them apart.
Does linking out hurt SEO?
No. Linking out does not hurt SEO by itself, and Google encourages it. Google's link documentation says "linking to other sites isn't something to be scared of; in fact, using external links can help establish trustworthiness (for example, citing your sources)" [6]. Its SEO Starter Guide adds that links "can provide more context on a topic, both for users and search engines" [7].
The old fear was "PageRank leak": the idea that every outbound link drains ranking value from a site. In the PageRank model, a page's value is divided equally among its outbound links [2], so each link does carry a share. But Matt Cutts advised against closing blog comments "in an attempt to 'hoard' your PageRank," adding that "parts of our system encourage links to good sites" [3]. A low outbound link ratio is not a goal. A site that never links out is less useful, not safer.
The risk is in what the outbound links are: paid links that pass ranking credit, links exchanged for links, or links to spammy sites [3][5]. A high ratio matters only because it is often how those links show up in the numbers.
What is the difference between outbound link ratio and link neighborhood?
Outbound link ratio measures how much a site links out, while link neighborhood describes who a site links to and who links to it. A site can have a modest ratio and still link to a bad neighborhood, such as gambling or pill sites, in a handful of posts. A site can also have a high ratio from linking to hundreds of legitimate sources.
Use the two together. The ratio flags a site worth a closer look. The neighborhood check, opening the outbound links and seeing where they go, decides what the ratio means.
How do you use outbound link ratio when vetting a site?
To use outbound link ratio when vetting a site, calculate it, compare it with similar sites in the same niche, and then inspect the actual outbound links in recent articles. Search Insider's process looks like this:
- Get the two numbers. Linked domains and referring domains from the same backlink tool, on the same day.
- Compare with peers. Check three or four genuine publications in the same topic. A site whose ratio is far above its peers needs explaining.
- Check the trend. If linked domains have climbed steeply over the past year while referring domains have not, the site is adding outbound links faster than it earns inbound ones.
- Read recent posts. Look for body links to businesses unrelated to the topic, keyword-rich anchors pointing at commercial pages, and the same kinds of clients appearing again and again.
- Look for a "write for us" or sponsored-post page. A site that openly sells placements will usually have a high ratio, and every link it places adds to it.
Outbound link ratio is a filter, not a verdict. A site that fails it should get a manual review before any decision. Search Insider does not support or suggest private blog networks, which typically show extreme ratios because their pages exist only to link out.
What should you do about your own outbound link ratio?
For your own site, do not manage outbound link ratio as a number. Link out whenever a source, tool or reference helps your readers, as Google recommends [6]. Mark paid and affiliate links with rel="sponsored" or rel="nofollow", and mark user-submitted links with rel="ugc" or rel="nofollow" [6].
If Google ever issues a manual action for unnatural links from your site, its recommended steps are to find links "that were paid for or that appear to violate our link spam policy," remove them or change them so they no longer pass PageRank, and then request a review [4].