Linked Domains vs Referring Domains: What Each Metric Counts

On this page: quick jump links

• What linked domains counts — and which way it points
• Linked domains, referring domains and backlinks, side by side
• Why two tools report different numbers for the same site
• Documented, versus widely believed
• What the number is actually good for
• Frequently asked questions

Linked domains is not one metric with one meaning. In Ahrefs it is an outbound count — the unique websites your site links out to — and it sits in Site Explorer under Outgoing Links. Almost everywhere else, people say it loosely to mean the opposite: the unique websites linking in to you, which most tools call referring domains. So the first question to ask about any such figure is not whether it is high, but which direction it points. Once direction is settled, a second gap appears: two tools measuring the same inbound link profile will still report different totals, because they disagree about what counts as one domain and about how much of the web they sample. This guide separates the three metrics people run together, and explains where the disagreement comes from.

What linked domains counts — and which way it points

Ahrefs defines the term without ambiguity in its own documentation: linked domains are the unique domains that a target website "links out to", also known as outgoing domains. The report lives under the Outgoing Links section of Site Explorer, not the backlinks section. DOCUMENTED — Ahrefs Help Center, "What are Linked Domains?".

That matters more than a naming quibble, because the two directions answer different questions. An outbound count describes editorial behaviour: how freely a site cites other people. An inbound count describes reputation: how many independent publishers thought your page was worth pointing at. Read one as the other and you will draw the wrong conclusion from the same number.

Ahrefs also documents a second use for the outbound figure, and it is the one most people miss. Its Domain Rating calculation takes this outbound count into account: the more domains a site links out to, the less of its own authority any single one of those links carries. DOCUMENTED — same source. In other words, the outbound count of a site that links to you is a rough proxy for how diluted that link is. A citation from a page on a site that links out to eighty thousand domains is not the same asset as a citation from a site that links out to two hundred.

Linked domains, referring domains and backlinks, side by side

Three numbers commonly appear within a few pixels of each other in link tools, and they are routinely quoted as if interchangeable. They are not. Backlinks counts individual links. Referring domains counts the unique sites those links come from. The third, in its documented sense, counts unique sites in the other direction entirely.

Metric	Direction	Unit counted	What a high number suggests
Backlinks	Inbound	Individual links	Volume — which may be one site linking a thousand times
Referring domains	Inbound	Unique linking websites	Breadth — independent publishers citing you
Linked domains (Ahrefs sense)	Outbound	Unique websites you link to	How freely the site cites others; dilution of its outbound authority

The inbound count is the one with the most aliases. Depending on which tool is open, the same underlying idea is labelled referring domains, linking domains, unique linking domains, linking root domains, or root domains linking to the page. CONSENSUS — the naming varies by vendor; the concept does not. If you are comparing two exports, match the definitions before you compare the totals, because the labels will not do that work for you. Our guide to backlinks explained covers why breadth beats raw volume once you have settled which column you are reading.

Why two tools report different numbers for the same site

Even after you have matched direction and definition, totals rarely agree. Three documented mechanics account for most of the gap, and Google Search Console's own Links report states all three plainly.

Domains are collapsed, but not consistently. Search Console groups its data by root domain: protocol and subdomain are stripped, so m.example.com, www.example.com and https://example.com all fold into one entry for example.com. Top-level domains are not stripped, so example.com and example.com.de stay separate. DOCUMENTED — Google Search Console Help, Links report. A tool that treats subdomains as distinct entities will therefore report a larger count of linking domains than one that folds them together, from an identical link graph. INFERENCE — this follows from the grouping rule; the size of the effect depends on how many of your links come from subdomains, which varies by site.

The report is a sample, not a census. Search Console states that its links report is not a comprehensive list of every link, that tables are limited to 1,000 rows, and that URLs may be omitted for reasons including non-indexed pages and deduplication. DOCUMENTED — same source. Any commercial crawler has the same constraint for a different reason: it reports the links its own crawler has found, not the links that exist.

The window is cumulative, not current. Search Console includes links it has found over time, and documents that those links may since have been removed or the page may no longer exist. DOCUMENTED — same source. Two tools with different retention and recrawl behaviour will disagree about a site's total simply because they are describing different moments.

The practical consequence: a count of root domains linking to your site is only comparable against itself, measured the same way over time. Cross-tool comparisons of absolute totals are close to meaningless. Trend within one instrument is the signal worth having.

Documented, versus widely believed

Widely believed: linked domains and referring domains are two names for the same inbound metric. Documented: in the tool whose help page ranks first for the term, they point in opposite directions — the first is filed under Outgoing Links and counts what you link to.

Widely believed: a gap between two tools' domain counts means one of them is wrong. Documented: the grouping rules differ, the crawl coverage differs, and at least one of them explicitly describes its output as a sample rather than a complete list. A gap is the expected result of two correct instruments answering slightly different questions.

Widely believed: more linking domains is straightforwardly better. Documented, in part: Ahrefs' own description of Domain Rating states that a site's authority is divided across the domains it links out to, which means the value of a new link depends on the linking site's outbound behaviour, not only on its authority score. Whether that generalises to Google's ranking systems is INFERENCE and is not something any vendor can document on Google's behalf.

What the number is actually good for

Three honest uses, in rough order of value.

As a diversity check on your own profile. Divide backlinks by referring domains. A ratio near one means many independent sites each linking once, which is the profile earned content tends to produce. A very high ratio means a small number of sites linking repeatedly — sitewide footer links, a widget, a directory network — which is a concentration risk rather than a win. What is a referring domain worth in that calculation depends entirely on whether it is genuinely independent of the others.

As a filter when assessing a prospective link. If a site's outbound domain count is enormous relative to its size, treat a link from it as a weaker signal. This is the dilution logic Ahrefs documents for its own metric, applied as a screening heuristic rather than a formula.

As a competitive gap, measured one way. Pull the count of unique linking domains for your page and for the pages currently outranking it, from the same tool on the same day. The absolute numbers do not matter. The order of magnitude does — it tells you whether the gap you are looking at is a content problem or an authority problem, which are not fixed by the same work. Our white hat link building guide covers the second case, and the Authority Engine module is how we run that work as a system rather than a campaign.

What the number cannot do is tell you whether a specific link helped. Attribution at that resolution is not available from any public tool, and a figure that moves after an outreach push has moved for many reasons at once. Related reading on how equity actually travels once a link exists: link equity and PageRank.

Frequently asked questions

What are linked domains?

In Ahrefs, they are the unique domains a website links out to — an outbound metric, documented as also known as outgoing domains and reported under Outgoing Links in Site Explorer. Used loosely elsewhere, the same phrase often means the reverse: the unique sites linking in to you, which most tools label referring domains. Because the term carries both senses in the wild, check which report a number came from before acting on it. The two describe entirely different things: one is how freely a site cites others, the other is how widely it is cited.

What is a referring domain?

A referring domain is a unique website that links to yours, counted once no matter how many individual links it sends. If one blog links to your page forty times, that is forty backlinks and one referring domain. The distinction matters because breadth of citation and volume of links are different signals, and volume is the easier of the two to manufacture. Vendors also label this same inbound idea linking domains, unique linking domains or linking root domains, so match definitions before comparing exports.

Are linked domains and referring domains the same thing?

Not in their documented senses. Ahrefs files the former under Outgoing Links and defines it as the domains a site links out to, while referring domains counts the domains linking in. They are opposite directions across the same boundary. In casual usage the terms are frequently swapped, which is exactly why a figure quoted without its source is unreliable — the number could describe your site's outbound citation habits or its inbound reputation, and nothing about the label alone resolves which.

How many referring domains do I need?

There is no threshold, and any specific figure offered without naming a query and a competitive set is invented. The useful version of the question is comparative: for the specific term you want, how many unique linking domains do the pages currently ranking have, measured in one tool on one day? That gives you an order of magnitude to close rather than a target to hit. Treat a number quoted with no query attached as marketing rather than measurement.

Why do different tools show different linking domain counts?

Because they group and sample differently. Google Search Console documents that it groups by root domain with subdomains and protocol stripped, that its tables cap at 1,000 rows, that the report is a sample rather than a comprehensive list, and that it includes links found over time which may since have been removed. Commercial crawlers apply their own grouping rules and report only what their crawler has found. Two correct tools answering slightly different questions will disagree, so track trend within one instrument rather than comparing absolute totals across two.

What does root domains linking mean?

It is another label for the inbound count: the number of distinct root domains linking to a page or site, with subdomains folded into their parent. Search Console applies exactly that rule, grouping m.example.com and www.example.com under one entry, while keeping different top-level domains separate. Tools that count subdomains as independent sites will report a higher figure from the same link graph, which is a definitional difference rather than an error by either one.