ACT Standard Deviation

One of the first things a lot of test-takers ask is “What’s a good ACT score?” There are a couple of ways of answering this; our ACT Score Range post takes a look at some of them. What we’ll do in this post is examine another way of evaluating scores, through the ACT standard deviation.

Instead of talking about good and bad ACT scores, I’ll break down the ACT bell curve to show you how your score stacks up against those of millions of other test-takers.

So if you’re ready, let’s crunch the numbers!

A Little Refresher

Let’s take a quick overview of bell curves and what they do (and don’t) show to get us started.


Liam got a 35 on the ACT. Get a higher ACT score with Magoosh.


This bell curve illustrates IQ distribution. The peak of the curve represents an IQ of 100. From this, we can see that 100 is the most common IQ, with the majority of people (68.2%) having an IQ of somewhere between 85 and 115.

Now, take a look at the edges of the graph. IQs lower than 85 or higher than 115 are less common. If you have an IQ of 130, for example, only 2.2% of the population has an IQ higher than yours.

Finally, the last important thing to note her is that the standard deviation of this bell curve is 15. That’s because each section goes up in 15-point increments.

Is there more to know about bell curves? Sure there is. But for the purposes of looking at ACT standard deviation, we have what we need to move forward!

ACT Standard Deviation

Now, imagine the same curve with the same percentages. One big difference: the numbers at the bottom have changed. The middle number is 20.8 and the standard deviation is roughly 4.7.

With those two little changes, we now have a bell curve that shows the distribution of ACT scores.

Let’s put this new graph to work. If you earned a 31 on the ACT, that would put you in roughly the same spot that a 130 IQ did on our previous graph. Therefore, we can see that people who earn a 31 do better that 97.8% of their peers.

What Does this Mean for Me?

Besides being a fun statistics exercise, ACT standard deviation is a powerful tool to see how competitive you are in the college application and scholarship field. If you’re planning on attending a less-competitive college, then a 21 (placing you slightly above average) is fine. Yet if you’re thinking about Harvard, your score should be as far to the right as possible.

But where would a 31 put you in terms of actual numbers? Cranking out the numbers, if you earned a 31 on the ACT, that would put you in the top 33,320 test takers. So even if you’ve earned a 31, you still have a lot of competition to get into one of America’s Top Colleges.

Final Thoughts

A good ACT score should only be one part of a well-rounded college application package. At the end of the day, prep your best, keep your grades as high as possible, and complete the best application that you can. As long as you do your research, and know what your top choice colleges expect, you’ll be just fine—or even several standard deviations above just fine.


  • Thomas Broderick

    Thomas spent four years teaching high school English, social studies, and ACT preparation in Middle Tennessee. Now living in Northern California, he is excited to share his knowledge and experience with Magoosh's readers. In his spare time Thomas enjoys writing short fiction and hiking in the Sonoma foothills.

By the way, Magoosh can help you study for both the SAT and ACT exams. Click here to learn more!

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