Ahrefs’ SEO Metrics Explained (Finally)

Tim Soulo
Tim is the guy responsible for marketing and product development at Ahrefs. But most importantly he’s the chief evangelist of the company.
    Most people think of Ahrefs as a powerful “backlink checker” tool. But in reality “checking backlinks” is just one of the many things that you can do with the huge data index that we have. 

    If you look at the big picture — Ahrefs is a data company. We collect data, we process data, we store data and finally we build all sorts of tools that let you tap into our data.

    In other words — we LOVE data! (the “big” one)

    Big data is a term for data sets that are so large or complex that traditional data processing applications are inadequate. Challenges include analysis, capture, data curation, search, sharing, storage, transfer, visualization, querying, updating and information privacy. 

    So before I explain the meaning behind our core metrics (as promised in the headline of this post), let me impress you real quick with the size of the data that is hiding behind the scenes.

    Ahrefs Data Index

    Here are a few core numbers representing the size of Ahrefs’ index (you can also find them on our homepage):

    Ahrefs-data-index-size

    In our index:

    • 12 trillion known links;
    • 2 trillion known URLs;
    • 200 million root domains.

    Powered by:

    • 10 petabytes of storage;
    • 100 terabytes RAM;
    • 5000 CPU cores.

    Every 24 hours our crawler visits over 5 billion web pages and updates our index every 15–30 minutes.

    Creating a robot that will crawl the web and store web pages on your hard drive might sound like an easy thing to do.

    But that’s until you try to achieve the crawl speed of 200 million pages per hour. Or try to store all this data in a way your customers can make a call to a database and have all their graphs and reports built in seconds.

    That’s why the major part of our backend infrastructure was built in-house. All existing solutions simply couldn’t cope up with the volume of data that we operate, or were too expensive (as of today we’re running a custom big data database with ~85 trillion rows).

    So as you can tell, we’re seriously obsessed with big data and we absolutely love all the challenges associated with it.

    Now let me explain the metrics that we have in our toolset.

    URL Rating (UR)

    Essentially “URL Rating” shows how strong a backlink profile or a target URL is on a logarithmic scale from 1 to 100 (with latter being the strongest). And how likely this URL is to rank in Google.

    URL Rating in "Backlinks" report

    URL Rating in “Backlinks” report

    Sidenote.
    “Logarithmic” means that it is much easier to grow your page from UR 20 to UR 30 than from UR 70 to UR 80. 

    We often see people explain Ahrefs’ URL Rating as a replacement for Google’s PageRank metric — but they’re not the same.

    We indeed started out with a PageRank-like formula, but then “UR” underwent quite a few iterations with a goal of creating a metric that would have the highest possible correlation with Google rankings.

    And as you can tell from the graph below, URL Rating correlates with Google rankings better than any of our “unprocessed” backlink metrics:

    backlink-factors-on-page

    Moz has a similar metric to our URL Rating called Page Authority, which predicts how well a specific page will rank on search engines. And according to their own study it correlates with Google ranking at 0.37.

    Sidenote.
    I don’t recommend you to rely on these numbers for direct comparison of “URL Rating” and “Page Authority”, because the dataset in each study was different. 

    Domain Rating (DR)

    This metric shows how strong the overall backlink profile of a given website is on a logarithmic scale from 1 to 100 (with latter being the strongest).

    Domain Rating in "Referring Domains" report

    Domain Rating in “Referring Domains” report

    This metric is not supposed to correlate with Google rankings, because one website can have both: high-UR pages that tend to rank well and low-UR pages that don’t rank.

    But DR is a perfect metric for picking websites to build links from. As a general rule, you need to aim to get backlinks from high-DR websites — because they carry more “weight”.

    Here’s a popular question that our customers ask about the DR of their own sites:

    Q: “I didn’t lose any of my backlinks. Why did my DR drop?”

    A: “That is because other sites have gained a lot of backlinks. Think of it this way: when DR-100 website gets more backlinks, we can’t make it DR-101. So instead we push all other websites down by 1. That is a very raw explanation of why you might see a drop in your DR while no backlinks were lost.”

    Ahrefs Rank

    If you take all the websites in the world and then order them by the size and quality of their backlink profile (basically by their DR) — you’ll get Ahrefs Rank.

    "Ahrefs Rank" of ahrefs.com domain is growing quite steadily

    Ahrefs Rank” of ahrefs.com domain is growing quite steadily

    So Ahrefs Rank #1 belongs to the website with the best backlink profile, #2 is just a bit worse, #3 is a little more worse, etc.

    You can see the full list of domains sorted by their Ahrefs Rank here.

    So if Alexa Rank shows you how much traffic a given website has relative to other websites in the world, Ahrefs Rank shows you how good its backlink profile is relative to other sites.

    Here’s the most popular question about Ahrefs Rank:

    Q: “My backlink profile is growing, but my Ahrefs Rank is going down. Why?”

    A: “Because other websites are getting new backlinks faster than you. What happens here is very similar to my above answer about drop in DR.”

    Live & Fresh Index

    As you’re browsing the backlink reports in Ahrefs’ Site Explorer tool you might notice a “Live/Fresh” switch that changes the numbers in your reports when you toggle it.

    "Fresh" index is bigger than "Live", because it contains links that are no longer there

    Fresh” index is bigger than “Live”, because it contains links that are no longer there

    What is the difference between the two?

    Like I’ve previously mentioned, Ahrefs index is updated every 15–30 minutes with all new backlinks that our crawler has found. But not only do we crawl new pages, we also re-crawl the old ones — and some of the links that we previously saw might disappear by the time we re-crawl that page.

    We will immediately remove all these “dead” links from our “Live” index, but they will stay in “Fresh” index for 3–4 months, so that you have enough time to act on this information.

    For example:

    Fresh” index shows me that Brian Dean used to have a backlink from Outbrain.com, but it got removed for some reason:

    Lost links are easy to spot in Ahrefs reports

    Lost links are easy to spot in Ahrefs reports

    I guess Brian could reach out to Outrbrain and persuade them to put it back. A link saved is a link earned, right?

    Keyword Difficulty (KD)

    This metric represents our estimation of how hard it would be to rank on the 1st page of Google for a given keyword and is measured on a logarithmic scale from 1 to 100 (with latter being the hardest to rank for).

    Our Keyword Difficulty score is based solely on the backlink numbers of the top 10 Google search results for a given keyword. Which means we do not take into account any on page seo factors.

    Sidenote.
    According to our recent study of on page seo factors, the usage of exact match keyword in Title/H1/URL/Content has an incredibly low correlation with Google rankings. That is why we do not have plans to include “exact match keyword usage” as one of the signals for calculating our Keyword Difficulty score. 

    Here’s a rough estimation of how many referring domains each KD score refers to:

    KD 0 = 0 Ref. Domains
    KD 10 = 10 Ref. Domains
    KD 20 = 22
    KD 30 = 36
    KD 40 = 56
    KD 50 = 84
    KD 60 = 129
    KD 70 = 202
    KD 80 = 353
    KD 90 = 756

    The team behind AuthorityHacker rececntly conducted a series of experiments to determine which Keyword Difficulty score was the most accurate.

    Ahrefs KD came number one, followed closely by Moz:

    number-of-wins

    Back To You

    So these were the metrics that we get asked about the most.

    I hope that this information will help you to better understand Ahrefs reports and make them more actionable.

    And if you have any other questions about the numbers that you see in Ahrefs reports — feel free to ask them in comments and I’ll be happy to answer them.

    Tim Soulo
    Tim is the guy responsible for marketing and product development at Ahrefs. But most importantly he’s the chief evangelist of the company.

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    • Olivier

      How do you get the non-geo positions for each country?
      when i Google something, my results are city-bound.

      • we get this data from our data providers, so I’m not exactly sure how they do it.

        • Olivier

          Then how can i be sure this isn’t a location based resultset?
          Or maybe this could be a nice feature request; show rankings for specific city/geolocations

    • Ashwin Chotoo

      Can you please clarify one thing please. I do understand UR and DR, but from a very basic position, please answer this question. When i am looking for sites to target for links, Should i be looking at the UR or DR. Which is a more precise snapshot of the website.

      • you should try to get links from domains with high DR and pages with high UR 😉

        • Hey Tim,

          I would much rather use this than Majestic so when buying expired domains is a good rule of thumb is gettin domains with a DR 40+ or will 30+ do well for a PBN site?

    • Thank u Tim Soulo

    • Jamie Richards

      I’ve genuinely been waiting for this for a long time!

    • Most important keyword metric is Keyword Difficulty (KD). KD is game changer for ranking keywords. Excellent work Mr. Tim Soulo

    • John Schnettgoecke

      Happy to see this article this morning. Thanks, Tim!

    • Victoria Lysenko

      Very nice article! Thank you!

    • Tim why does a domain have show different UR, for example my non www version and the www version both have different UR. Which one should I trust? Why is that?

      • UR stands for “URL Rank”… http://www.domain.com and domain.com are technically different URLs 🙂 Hope that makes sense

        • Thanks Tim I figured that was it. I have a REQUEST that everyone will appreciate and now that I am talking to boss I will ask. On the Standard Plan you should definitely change the position tracking to TOP 100 not TOP 50. To jump from the Standard Plan to the Advanced is a big price jump. Top 50 just does not cut it. Can you make it happen for all of your users? We would all appreciate that.

    • > Is this # of RD’s (dofollow AND nofollow)?
      yes.. that’s a total # of RDs

      > If it’s total what happens if the #1 has 1000 RD’s, and the rest 9 results have 10 RD’s in total, will the KD be 90?
      we remove outliers before calculating average 😉

      • I have a similar question to Ian’s.

        Does UR take nofollow referring domains in to consideration?
        If it does that will be very misguiding.

        Preferably UR should be based only on dofollow referring
        domains.

    • Top Content vs Top Pages. From what I can see content is by shares and top pages is by links. Are there any other differences?

    • Tim, if a site has incoming links that point to pages that have been removed and not redirected (i.e. they return a 404 or 410), are those links ignored for purposes of DR?

      What if they are 301 redirected to another page? Is that treated exactly the same as a direct link to that destination page, is some link juice lost in the redirect, or is it ignored? (thinking about both DR and UR)

    • Việt Hùng Ase

      I can’t see full list of domains sorted by their Ahrefs Rank, you can fix it.

    • According to Ahrefs data,URL Rating (UR) is the most ranking factory. Well, my question is that, when I got a editorial dofollow backlink from DR 80+, but when I analyzed that backlink from Ahrefs, it shows DR 80+, but show UR only 30+ or 40+, how you analyzed backlink UR rating. How can i improve my UR rating from DR 80+ editorial dofollow link. If I am getting an editorial dofollow backlink from DR 80+, then why not my UR is 70+ or 80+. How can i improve my UR rating for backlink from DR 80+? Well Please answer Mr @timsoulo:disqus

    • I have been always forget what the actual meaning of these short-forms while using ahreafs. Thank you for sharing.

    • I was using ahref for a while but saw this info now. many new things i did not know thank you 🙂

    • result togel

      Top Content vs Top Pages. From what I can see content is by shares and top pages is by links. Are there any other differences?

    • happy tu read your article, thanks for sharing, helpfull explanations

    • Its really a good article but how do i increase domain rating.

    • Great Tips for the seo. It is very useful for my website. Good sharing..

    • Its really a nice post and it is very useful for my website.

    • Very good analisys!

    • So, I’m a bit confused on just the Ahrefs rank portion. Using Ahrefs, we have been working diligently to procure backlinks for a client of ours, and have been extremely successful, getting .edu links, etc. Their UR rank has increased tremendously, DR rank has stayed the same, yet their Ahrefs rank has gone down pretty substantially. Their keywords have increased, along with site traffic, and we are in the process of fixing their site errors. Something isn’t adding up.
      Meanwhile, I’ve been using my website as a comparable, using the same methodology, and everything is steadily rising in all categories. It seems as if something is amiss.
      Great article. Thank you.