The 31 Critical ACT Math Formulas You MUST Know

The two biggest challenges of the ACT math test are the time crunch--the math test has 60 questions in 60 minutes!--and the fact that the test doesn’t provide you with any formulas. All the formulas and math knowledge for the ACT comes from what you’ve learned and memorized.

In this complete list of critical formulas you'll need on the ACT, I'll lay out every formula you MUST have memorized before test day, as well as explanations for how to use them and what they mean. I'll also show you which formulas you should prioritize memorizing (the ones that are needed for multiple questions) and which ones you should memorize only when you've got everything else nailed down tight. 

Already Feeling Overwhelmed?

Does the prospect of memorizing a bunch of formulas make you want to run for the hills? We've all been there, but don't throw in the towel just yet! The good news about the ACT is that it is designed to make anyone be able to succeed. Many of you will already be familiar with most of these formulas from your math classes.

The formulas that show up on the test the most will also be most familiar to you. Formulas that are only needed for one or two questions on the test will be least familiar to you. For example, the equation of a circle and logarithm formulas only ever show up as one question on most ACT math tests. If you’re going for every point, go ahead and memorize them. But if you feel overwhelmed with formula lists, don’t worry about it--it’s only one question.

So let’s look at all the formulas you absolutely must know before test day (as well as one or two that you can figure out yourself instead of memorizing yet another formula).

Algebra

Linear Equations & Functions

Logarithms

Statistics and Probability

Probabilities

Combinations

Percentages

Geometry

Rectangles

Area

Area=lw

• l is the length of the rectangle
• w is the width of the rectangle

Perimeter

Perimeter=2l+2w

Rectangular solid

Volume

Volume=lwh

• h is the height of the figure

Parallelogram

An easy way to get the area of a parallelogram is to drop down two right angles for heights and transform it into a rectangle.

• Then solve for h using the pythagorean theorem

Area

Area=lh

• (This is the same as a rectangle’s lw. In this case the height is the equivalent of the width)

Triangles

Area

• 12bhb is the length of the base of triangle (the edge of one side)
• h is the height of the triangle
• The height is the same as a side of the 90 degree angle in a right triangle. For non-right triangles, the height will drop down through the interior of the triangle, as shown in the diagram.

Trapezoids

Circles

Trigonometry

But Keep in Mind

Though these are all the formulas you should memorize to do well on the ACT math section, this list by no means covers all aspects of the mathematical knowledge you’ll need on the exam. For example, you’ will also need to know your exponent rules, how to FOIL, and how to solve for absolute values. To learn more about the general mathematical topics covered by the test, see our article on what's actually tested on the ACT math section.

@harvarded