Backlinks Analytics on SEMrush use three metrics to measure the impact of a webpage or domain’s links.
Page Score and Domain Score measures the importance of a web page or domain on a 100 point scale based on the volume of links pointing back to the page or domain. In this case, volume represents link “weight,” or the cumulative volume from the number of backlinks pointing to the page that points to the target page and so on. This way of calculating with cumulative link weight is similar to the way Google PageRank was calculated.
Domain Score is calculated for the entire domain, while page score is calculated for an individual page (URL). The quality of links are not taken into account to calculate this metric; only the volume.
Trust Score, however, measures the trustworthiness of a webpage or domain (also on a 100-point scale) based on the number of links coming from highly trusted websites. Since Trust Score places more emphasis on high quality backlinks, if you notice a big difference between Trust Score and Page Score on your website, you may be a victim of having too many low quality backlinks.
Since the quality of backlinks plays an important role in SEO, you’ll want to use Trust Score to understand which link prospects will be more or less beneficial to acquire.
Since the impact of a link is dependent on how relevant the link is, it is hard to say a backlink needs to reach a concrete number with Page Score or Trust Score to be effective. In general, somewhere over a score of 20 (for both metrics) can be considered healthy, and as the score increases, the impact of a link will increase. However, the impact of a link also strongly depends on your website’s niche.
The main use for these scores is to compare and sort. For example, use the scores in the Backlinks Comparison or Quick Batch reports to compare the trust levels of multiple websites. By comparing these scores you can evaluate which domain’s link profile is strongest and will send the most link weight when linking to other sites.
If you compare the Trust Score to the Page Score or Domain Score of a site and notice that the Trust Score is much lower than the Domain Score, it can be a sign of unhealthy links, or cheap link building tactics. When Google sees a website that appears to have a high number of low quality links, they are inclined to give the website a Google Penalty. To avoid receiving a Google Penalty, you can run a Backlink Audit and create a disavow list with all of the most potentially harmful links.
These scores can be found in the Backlinks report, Referring Domains report, Backlinks Comparison, Quick Batch and Backlinks Overview. Set the report scope from “Root Domain” to "URL" and Backlinks Analytics will display Page Score rather than Domain Score in your report.
Trust Score in the Backlinks report will represent the quality of the source page, and Trust Score in the Referring Domains report will represent the quality of the source domain. For more on changing your settings while analyzing backlinks, refer to the Backlinks Analytics user manual.