Data Accuracy: SEMrush vs Similarweb vs Ahrefs

Data Accuracy: SEMrush vs Similarweb vs Ahrefs

There are many tools for competitor benchmarking. However, each of them collects traffic data and processes it in a different way. And you can’t expect them to be 100% accurate. Given this, which tools are accurate enough so that you can use the results for meaningful analysis?

  There is no 100% correct solution out there.

There is always a degree of incorrectness when analyzing the data for the final results. This is known as the error rate, which is about 6% on average. At Similarweb, it’s about 20%, and in some areas, it’s over 80%.

See our little research below based on collected data.

Compare Accuracy with Techjury’s user statistics: SEMrush vs Similarweb vs Ahrefs vs Google Analytics

1. Check Techjury’s user engagement for 30 days. In the process, I compared these metrics to data from Ahrefs, Semrush, and Google Analytics.

What were the results?

Data from Google Analytics is as accurate as it can get. From the above image, it gave monthly visits of 272,331. Ahrefs came close with a traffic of 298,987

As for Semrush and Similarweb, I got 442,600 and 700,583 clicks respectively. Using Google’s results as a reference, the margin of error would look like this.

  • Google Analytics – 0%
  • Ahrefs – 9.33%
  • Semrush – 47.63%
  • Similarweb – 88.03%

The difference in results extends to other metrics as well. These include new visitors, bounce rate, session duration, etc.

So, what does this mean?

Unfortunately, the accuracy of the results provided by Similarweb is questionable.

While it’s a good tool, Similarweb could have better traffic reporting.

  Similarweb Review
  Daniel Wabuge, Techjury

Compare Accuracy with 787 websites: SEMrush vs Similarweb vs Google Analytics

The higher the standard deviation, the greater the inaccuracy of the data for a given service compared to the Google Analytics benchmark. SimilarWeb deviates between 57% and 61%, with no relationship to site traffic. SEMrush data shows a clear trend: sites with huge traffic (1,000,000 or more) show higher accuracy, with Google Analytics data showed less deviation (45%).

For websites with 500,000 sessions or more, the numbers were 9 to 12 percentage points more precise in SEMrush. For projects with little traffic, SimilarWeb worked slightly better, but both services demonstrated large inaccuracies among this group of websites.

These differences in accuracy are caused by the collection and processing algorithms of SimilarWeb and SEMrush as well as special aspects of clickstream data. Traffic analysis services use artificial intelligence and machine learning algorithms to approximate data on all website visitors based on clickstream data, which is data on samples of website traffic. Thus, the smaller the website, the less accurate the approximations based on clickstream data.

What should you do if your website and your competitors’ sites have low traffic and the accuracy of your data is extremely low? In this case, you should benchmark against bigger competitors in your market. If you compare some big market players, you’ll see not only their performance but also the general market trends. And by comparing performance and trends revealed by SimilarWeb or SEMrush with your own achievements, you’ll be able to see the efficiency of your marketing.

The graph below describes the share of observations — the percentage of websites within each segment for which SimilarWeb and SEMrush respectively were closer to the Google Analytics benchmark. For example, in the 1,000,000+ sessions segment, SEMrush gave more accurate data than SimilarWeb for 57% of analyzed websites:

By comparing the 100,000 to 500,000 sessions segment in the Standard deviation and Share of Observations graphs, we discover an interesting insight: SEMrush data has a higher standard deviation, which tells us that the session approximations are generally less accurate. At the same time, SEMrush is still more precise in 53% of cases. Long story short, SEMrush makes fewer mistakes but the mistakes it does make tend to be massive.

The accuracy of data depends on a variety of factors:

  • How Google Analytics is set up, which pages have GA tags, and what exactly those tags measure.
  • How active the website is on Google. For a redirect website like from an advertising network or a promo website with massive paid ad traffic, SEMrush will show lower numbers.
  • How big the share of organic traffic is for the website. SEMrush is likely more precise for sites with a larger share of organic traffic.
  • The region and business sphere. Let’s suppose SEMrush has more projects from the US. In this case, it will have more data from the US and calculations for US sites will be more accurate.

The next two graphs demonstrate the standard deviation and share of more accurate data from both services segmented by business sphere.

As you can see, the deviation of both SEMrush and SimilarWeb depends on the business sphere:

The percentage of websites for which SimilarWeb and SEMrush were closer to the Google Analytics benchmark also depends on the business sphere:

For example, in the Computers sphere, SimilarWeb was more accurate for 58% of websites and SEMrush was more accurate for 42% of websites (the first column in the graph above).

This dot graph shows the positive and negative deviation values for SEMrush (blue dots) and SimilarWeb (green dots):

Even visually, you can conclude that the lower part of the graph has more green dots, which means that SimilarWeb is more likely to show values lower than the real traffic data from Google Analytics.

Comparing accuracy: SEMrush vs SimilarWeb

Marie Sharapa, OWOX BI
  Comparing accuracy: SEMrush vs SimilarWeb
  Marie Sharapa, OWOX BI

To sum up

We found that:

  • The accuracy of SimilarWeb and SEMrush is similar.
  • SEMrush showed better results for medium-sized websites. Mistakes were rare, and if mistakes were avoided, the data was more accurate.
  • In the 1,000,000+ sessions segment, SEMrush was more accurate than SimilarWeb.
  • SimilarWeb is more likely to underestimate traffic volumes.

What’s important to remember is that no tool can guarantee you 100% accuracy. To analyze your own website data, you have Google Analytics. But SimilarWeb, SEMrush and Ahrefs are sufficient for comparing sites independently and identifying trends. However, when using any analytics tool, you should be aware of the sources of the data collected and the biases measured.

The thing about website traffic estimators is that while they won’t provide the ultimate accuracy of the data, they can be used perfectly as a benchmark. And the key things to keep in mind when analyzing traffic data from your market and competitors are.

  • Don’t look at absolute numbers.
  • Think of all traffic data as relative. This means you can run your own site through the tool, get certain numbers, and then look at the competition and evaluate their online performance metrics relative to yours.
  • Let’s say if their traffic exceeds yours by 5%, you can add your real traffic count (gathered from Google Analytics) to 5% and get an accurate absolute view.

However, in this case, you really don’t need absolute numbers. What you really get is an accurate benchmark that you can compare to your performance


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