Expelliarmus is one of the most memorable spells that Harry uses in the series. He gained freedom from Voldemort while using it in the Battle of Hogwarts. But he was advised to change his approach because he could not be expected to win by simply disarming Death Eaters. Although many would say that it is one of the most commonly used spells in the movies, my research does not support that claim. Expelliarmus is actually near the end of my list. But which ones are above then? Some of them surely come to your mind. And I believe you will be surprised. But before we start, I would like to tell you more about research itself.
I watched all the movies once more (probably for the hundredth time) and took a note of every spell that was used. There's a lot of them! Especially as the serial moves on. It is interesting to note that Harry did not use a single spell in the first film Harry Potter and the Sorcerer’s Stone unlike the rest of the films where numerous spells are used. Most of the spells used were noted, though there were a few issues with doing that.
Firstly, there are non-verbal charms and spells, many of which I managed to note, taking into account colour of the charm, context, reactions to it and the same events as they were described in the books. Of course, some of them I could not get a hold of, especially in great battles, and I did not want to make guesses. Unfortunately, as long as none of the people who made the movie or J.K. Rowling herself says exactly which spells were used, our list cannot be complete.
The second problem was keeping track of the spells. In moments when many different people use the spell, it is almost impossible to count all of them. In spite of that, many of them were counted anyway. All in all, I managed to note down roughly about 95% of the spells. The battles were the most problematic. You can see the list and the explanation in the infographic below as well as in the rest of the text.
