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Thomas Broderick

ACT Standard Deviation

Good day, Magooshers. Mr. B here. Hope everyone is having a nice summer break. School is just around the corner, though. If you’re an upcoming high school junior or senior, a statistics class might be in your future. To get you mind ready for statistics, this article contains some important information: ACT standard deviation.

Instead of talking about ‘good’ and ‘bad’ ACT scores, I’ll break down the ACT bell curve to determine how your score stacks up against those belonging to millions of other test takers. So if you’re ready, let’s crunch the numbers.

A Little Refresher

As you may not know everything about bell curves, here’s one to get us started.



This bell curve measures the IQ of everyone on Earth. The peak of the curve represents an IQ of 100. 100 is the most common IQ, with the majority of people (68.2%) having an IQ of somewhere between 85-115. Lower and higher IQs are less common. If you have an IQ of 130, for example, only 2.1% of the population has an IQ higher than yours. The standard deviation of this bell curve is 15, 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 this article, we have what we need.

ACT Standard Deviation

Now imagine the same curve with the same percentages. The numbers at the bottom have changed. The middle number is 21 and the standard deviation is roughly 4.7. With those two changes we have made 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 at roughly the same spot that a 130 IQ did on our previous graph. Therefore, we know that people who earn a 31 do better that 97.9% of their peers. Isn’t that nice?

What does this mean?

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. Planning on community college? Then a 21 is fine. Yet if you’re thinking about Harvard, your score needs to be as far to the right as possible.

But where would a 31 put you in terms of actual numbers? I’ve done the math, and 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

As I’ve said before, a good ACT score should only be one part of a well-rounded college application package. At the end of the day, grades matter most. Commit to one or two extra-curricular activities, too. As long as you do your research, and know what your top choice colleges expect, you’ll be fine.

Till next time, Magooshers.

About 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.

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