In the two decades before The Phantom Menace, fans lived with the idea that anyone could obtain the powers of the Force and become a Jedi with enough training and discipline. Then, in 1999, Jedi master Qui-Gon Jinn reveals to a young Anakin Skywalker that the Jedi Order tests younglings for microscopic life forms that are in all living cells and apply the power of the Force to their hosts. The higher the midi-chlorian count, the more powerful the holder can be with the Force. This is never mentioned in the previous trilogy and changes the pre-conceived notion of how to gain the powers of the Force.
When Qui-Gon discovers that the boy has an astonishing midi-chlorian count of over 20,000, which is more than Yoda’s, he knows that Anakin has the potential to become a great Jedi. He is not more powerful than Yoda at the time, but he could be with the right training and if he’s more receptive to the Force itself. This is why one of Anakin’s strongest abilities is the ability to see the future, as he unintentionally does so with his dreams about Padme and his mother dying. His immense power contributes to his paranoia and turn to the Dark Side.
Exactly how many midi-chlorians Anakin has in his system is not confirmed in the movies, but George Lucas himself reveals that he is potentially twice as strong as Emperor Palpatine. In an interview with Vanity Fair, Lucas states, “his ability to be twice as good as the Emperor disappeared, and now he’s maybe 20 percent less than the Emperor.”
There are plenty of unofficial lists of midi-chlorian counts for each character, but the general consensus, as seen in Rich Smith’s Quora’s post, is that Darth Sidious has about the same amount or slightly more than Yoda. If Yoda and the Emperor’s midi-chlorian count is just under 20,000, then Anakin possibly has nearly 40,000. Of course all of the potential Anakin had to become the most powerful Force user is lost after losing several limbs and suffering from severe burns in the Battle on Mustafar against Obi-Wan Kenobi.
Emperor Palpatine still has a very good apprentice in Darth Vader, but, as Lucas reveals later in the interview, the Emperor didn’t expect an apprentice weakened so much by one critical battle. This is why the discovery of Vader’s son, Luke Skywalker, excits Sidious so much. Lucas confirms that Luke has the same Force potential as his father, claiming that, “[the Emperor] finds that, with Luke, he can get a more primo version [of Anakin] if he can turn Luke to the Dark Side,” which means Luke most likely has the same midi-chlorian count as his father.
However, Sidious is also terrified when he finds out Luke was trained by Obi-Wan and Yoda. If Luke reaches his full potential as a Jedi, he can destroy Vader and the Emperor easily. His midi-chlorian count also explains why Luke becomes a master so quickly despite spending little time with Obi-Wan and Yoda while they’re alive. While driven by the Light, Luke does falter at times, and Sidious is thrilled to see Luke on the verge of destroying Vader in Return of the Jedi because he sees a stronger version of Anakin; however, the will of Luke is uncorrupted, and he brings his father back to the Light Side.
Although, Lucas claims to have come up with the concept of midi-chlorians during the production of the original Star Wars trilogy , it does not make the final script for these films. When he introduces it for the prequel trilogy, a new explanation for Anakin’s immense power is provided, and in turn, so is the reasoning behind why Luke is so connected with the Force and why the Emperor wants him so badly on the Dark Side.
Looking back at other force users, it's clear Luke's midi-chlorian count is as high, if not higher, than Anakin's at his best.