Keyword Difficulty Vs Backlink Profile [A Case Study on Semrush and Ahrefs]

Keyword Difficulty Vs Backlink Profile [A Case Study On Semrush And Ahrefs]

Ever wondered how many backlinks you exactly need to rank in the first position? Do keyword research tools (like Semrush and Ahrefs) Keyword Difficulty (KD) scores do justice in this case?

Theoretically, the harder a KD score is, the more backlinks you’ll require to grab the top position of the SERP. But I’ve seen multiple websites ranking in top positions without any backlinks. Even though the Semrush KD and Ahrefs KD were labeled “Hard”. 

So, I thought of experimenting with 4 growing websites and building a relationship between their backlink profile and KD scores. 

What’s My Goal from this Study?

My primary goal is to check whether KD scores really help in setting up a niche website’s backlink profile. So, I built the following questions to support my study.  

  • What’s the relationship between Semrush KD and Ahrefs KD?
  • Is it possible to rank with a specific number of backlinks based on KD scores? 
  • Can KD determine the number of referring domains to rank your content?
  • Does KD scores help rank in the top 3 positions with zero backlinks?    

I conducted individual experiments to figure out the answers. So, keep reading to learn how I did it. 


For this case study, I analyzed 4 random websites containing 839 keywords in total. I only took the main keywords from those websites ranking in positions 1-20. To keep it simple, I labeled the keywords “Ranking” for positions 1-3 and “Not Ranking” for positions 4-20. 

Here’s a profile summary of the 4 websites. 



Domain Rating

Authority Score

URL Rating 

Semrush Ranking

Website 1






Website 2






Website 3






Website 4






Tools Used

  • Google Sheets: For recording and analyzing data.
  • Semrush and Ahrefs: For exporting ranking and backlink data.

Well, I actually didn’t need all of the ranking and backlink data the tools suggested. Here’s what I only considered-

Ranking Data: Pages, Main keywords, Positions, Semrush KD, and Ahrefs KD.

Backlink Data: No. of total Referring Domains, No. of Total Backlinks, Backlinks Nofollow, and Backlinks Dofollow.

Data Analysis

For data analysis, I plotted graphs on Google Sheets based on the database. I used average aggregate data in this case so that it’s easier to visualize multiple data points on the same factor. 

So, before diving straight into the case study, I want to put a disclaimer here. Don’t take this study as an ideal scenario for keyword research. The study is only limited to 839 keywords and 2 keyword research tools. You might see different results considering more than 2 keyword research tools and a bigger database.   

Alright. So, let’s head towards the case study.

#1. Relationship Between Semrush KD and Ahrefs KD Scale


  • Ahrefs KD score has a positive and linear relationship with Semrush KD score.
  • For the same KD score, Ahrefs has more weight than Semrush.

While working with the KD scores, I realized Semrush and Ahrefs don’t have an equivalent scale. Where Semrush considers (0-49) KD as Easy, it’s (0-10) KD score for Ahrefs.

So, I tried to plot a relationship between the two scales from the 4 websites. Here’s the graph for 860 keywords showing the relevancy between Semrush KD and Ahrefs KD.

Ahrefs KD Vs Semrush KD

So, basically, it’s a linear relationship. According to the graph, the formula looks like this: 

Ahrefs KD = 0.713*x ±10.1 [where, x= Semrush KD]

This means Ahrefs puts more weight on each KD score than Semrush when labeling it as “Easy”, “Medium”, or “Hard”.

For example, if you compare Ahrefs KD=5 and Semrush KD=5, Ahrefs considers more factors than Semrush on that particular point.

# 2. Relationship Between Total Backlinks and Keyword Difficulty


  • Both Semrush KD (correlation: 0.37) and Ahrefs KD (correlation: 0.44) don’t entirely depend on the total number of backlinks. 
  • For the “Easy” KD level, Semrush requires around 12 backlinks while Ahrefs requires around 25 backlinks.  
  • In the case of the “Medium” KD level, it’s 39 backlinks for Semrush and 38 backlinks for Ahrefs.
  • For “Hard” KD levels of Semrush, the websites took 73 backlinks whereas the number is 66 for Ahrefs “Hard” KD level.   

I found a total of 202 keywords from the 4 websites which are ranking in positions 1-3. I have categorized the keyword difficulty levels as Semrush suggested; (0-14) = Very Easy, (15-29) = Easy, (30-49) = Possible, (50-69) = Hard, (85-100) = Very Hard. 

So, after plotting the total number of backlinks against Semrush KD scores, the graph looks like this. 

Position (1-3): Semrush KD Vs Total Backlinks

From the graph, one thing is clear. The higher the KD score is, the more backlinks you’ll require to rank in the first 3 positions. 

My analysis of these 4 websites shows that it takes around 6 backlinks for Semrush KD (0-14), 19 backlinks for Semrush KD (15-29), 39 backlinks for Semrush KD (30-49), 56 backlinks for Semrush KD (50-69), and 90 backlinks for Semrush KD (70-84).  

Positions (1-3): Ahrefs KD Vs Total Backlinks

Similarly, I considered Ahrefs predetermined Keyword Difficulty Levels: (0-10) = Easy, (11-30) = Medium, (31-70) = Hard, and (71-100) = Super Hard. 

So, the study shows that the 4 websites have around 25 backlinks for Ahrefs KD (0-10), 38 backlinks for Ahrefs KD (11-30), and 66 backlinks for Ahrefs KD (31-70). These data are for only pages ranking in the top 3 positions.

#3. Relationship Between Referring Domains and Keyword Difficulty


  • Ahrefs KD leans more towards Referring domains than Semrush KD.
  • It’s possible to rank with few referring domains than Ahrefs suggestion for “Hard” KD scores. 
  • For “Easy” KD scores, it took around 5 referring domains in the case of Semrush KD and 9 referring domains for Ahrefs KD. 
  • For “Medium” KD scores, Semrush KD supports 14 referring domains and Ahrefs KD supports 13 referring domains.
  • For “Hard” KD scores, Semrush KD supports 23 referring domains and Ahrefs KD supports 20 referring domains.         

I’ve considered 202 keywords for this case also that are ranking in the top 3 positions of the SERP. I wanted to check if the number of referring domains needs to increase while aiming for a higher KD score. 

First I calculated their correlation to each other. The correlation of Total Referring Domains with Semrush KD is 0.38 whereas, for Ahrefs KD, the number is 0.41. This means Ahrefs KD considers referring domains more than Semrush KD. 


So, how does it look in a graph? Here’s what I found in the case of Semrush KD.  

Positions (1-3): Referring Domains VS Semrush KD

From the graph, you can see that the referring domain isn’t constant as the KD score rises. So, I calculated the average of referring domains against Semrsuh’s different KD scores. I found it definitely takes more referring domains to rank in the top 3 positions for high KD. 

Here are my findings,

For Semrush KD-

  • 0-14 (Very Easy): 3 Referring Domains;
  • 15-29 (Easy): 7 Referring Domains;
  • 30-49 (Possible): 14 Referring Domains;
  • 50-69 (Difficult): 17 Referring Domains;
  • 70-84 (Hard): 30 Referring Domains.
Positions (1-3): Referring Domains Vs Ahrefs KD

In the case of Ahrefs, the pattern is similar to the Semrush KD. But I noticed a slight contradiction with Ahrefs suggestion. 

While my analysis supports Ahrefs’ suggestion for “Easy” and “Medium” KD, it shows irregularity for the “Hard” KD score. 

Ahrefs says you’ll need less than 10 domains to rank for “Easy” KD (0-10) and around (11-36) domains for “Medium” KD (11-30). My study shows it took around 9 domains for “Easy” KD and 13 domains for “Medium” KD keywords to rank in the top 3 positions of the SERP. 

But it took around 20 domains to rank for a “Hard” KD score (31-70) whereas Ahrefs says you’ll require (37-200) referring domains. 

So, does this mean you can actually rank with fewer referring domains than Ahrefs suggestion? This case study is proof that you can. I think probably it’s because the competitors were less powerful in this case.

#4. Relationship Between Keyword Difficulty and Average Keyword Position Having Zero Backlinks


  • It’s possible to rank with zero backlinks for Ahrefs “Easy” and “Medium” KD scores.
  • For Semrush, the scale is from “Very Easy” to “Easy” KD scores. 

Now, I wanted to check if it’s really possible to rank with zero backlinks and a high KD score. So, I filtered out the keywords ranking from positions (1-5) having no backlinks. From 4 websites, I only found 29 keywords that meet these criteria. 


After plotting Semrush KD and Ahrefs KD scores against the position, here’s what the graph shows. 

Position (1-5): Semrush KD Vs Ahrefs KD for 0 Backlinks

The graph shows that the 4 websites were capable of ranking in the top 5 positions without any backlinks for “Easy”(0-10) and “Medium”(11-30) Ahrefs KD scores only. It has been possible for both “Very Easy” (0-14) and “Easy”(15-29) in the case of Semrush KD scores.


So, as a niche website owner, you can definitely use Semrush and Ahrefs KD scores to rank w/wo backlinks on the top positions of the SERP. But you should be aware of the other factors impacting the KD scores as well. In my next case study, I’ll try to build a relationship between Keyword Difficulty and Ranking Data. So, stay tuned! 

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