Unlike the SAT, the ACT does not provide you with a list of basic math formulas to rely upon at the beginning of the ACT math test. This means you will need to be able to recall math formulas on the ACT. Below you will find lists of “Must Know” ACT math formulas, “Good to Know” formulas, and “Bonus” formulas to commit to memory for the ACT! Learn them all, then check out our list of ACT math topics to begin applying them!
MustKnow ACT Math Formulas
Though the ACT tests different concepts on each exam, there are popular topics that come up again and again. This list contains the best ACT math formulas to know. For more practice, try Magoosh ACT prep.

Average:
 S/T (Average = Sum/Number of things)

Lines:
 Slope intercept form:
 Slope:

Quadrilaterals:
 Perimeter of a rectangle:
 Area of a rectangle:
 Volume of a box:
 Surface area of a rectangular solid:
 Diagonal in a rectangular solid:

Triangles:
 Area of a triangle:

Circles and Spheres:
 Area of a circle:
 Circumference of a circle:
 Volume of a sphere:

Cylinders:
 Volume of a cylinder:

Pythagorean Theorem:

Trigonometry:
 SOHCAHTOA:
 You should also know your quadrants and where sine, cosine, and tangent are positive or negative:

Probability:
 Probability:
 Factorials (e.g. 8!):
 Equation of a circle:
 Volume of a cone:
 Volume of a pyramid:
 Arithmetic sequences:
 Geometric sequences:

Logarithms
 Definition:
 Change of base rule:

Trapezoids
 Area of a trapezoid:
 306090 Triangle Ratio:
 454590 Triangle Ratio:

Exponential Growth Formula:

Quadratic Equation:

Permutations:

Combinations:
y = mx + b (where m is the slope and b is the yintercept)
2l + 2w (where l is the length and w is the width)
lw (length x width)
lwh (length x width x height)
2lw + 2wh + 2lh
Apply the Pythagorean theorem twice or
1/2bh (1/2 base x height)
sin x = opposite/hypotenuse
cos x = adjacent/hypotenuse
tan x = opposite/adjacent
Number of desired outcomes / number of total outcomes
To find the factorial of any integer, multiply it by every positive integer below it, e.g.:
8 x 7 x 6 x 5 x 4 x 3 x 2 x 1
Bonus: the “Must Know” math formulas on the ACT also appear in your high school math classes. So, you’re really studying for two things at once. Nice.
Formulas that are Good to Know
(Add the bases, divide by two, then multiply by the height.)
Triangles
Where P = principal (starting value), r = rate of growth, n = number of months, t = time in years, and A = new amount.
Bonus Things to Know
Often, you will be better off applying a strategy such as backsolving to solve a complicated algebra problem, but if you are comfortable with the quadratic equation, keep it in the back of your mind.
An Important Note About ACT Math Formulas
Occasionally, an ACT math problem may rely upon a more advanced formula, such as the surface area of a sphere. In these cases, the question itself will typically provide you with the formula you need. So no need to think you need to memorize everything. However, being able to recall basic formulas will ensure you can tackle problems that don’t provide a formula with confidence! The list below includes formulas for the concepts the ACT tests most frequently.
Important ACT Math Formulas to Know (PDF)
Sometimes it’s easier to memorize formulas by studying a little bit every day. To make this easier, we created a printable Magoosh ACT Math Formulas PDF. Here’s the link where you can get your copy.
Let us know if you have any questions about these ACT formulas. 🙂
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