Inverse Cosine Calculator arccos(x)

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Below is an inverse cosine calculator (or arccos calculator), which calculates an angle from the ratio from the cosine function. Enter the result and choose to return radians or degrees, then compute the angle.

Inverse Cosine Calculator

Using the Arccosine Calculator

To use the tool to find the angle from a cosine, enter the ratio, choose the units you'd like as output, and compute.

  • Cosine - ratio of the adjacent side over the hypotenuse
  • Output Degrees or Radians? - choose to return degrees or radians

Once you're happy, click the "Compute Arccos" button.

  • Angle - the angle you'd input if you wanted to get the cosine you entered

What is the arccosine or inverse cosine?

Arccosine is the inverse of the cosine, which is the ratio of the adjacent side over the hypotenuse (longest side) in a right triangle.

Right triangle to illustrate trigonometry functions
Right Triangle Diagram (CC By-SA 3.0 Wikimedia)

The adjacent side can never be larger than the hypotenuse as it can at most match the length. This means arcsine can only be between -1 and 1.

Arccosine as a formula

Inverse cosine is usually abbreviated as "arccos" or "acos", as in the following equation:

arccos(y) = acos(y)

Where it is the inverse of cosine, or:


Next, see all the inverse trigonometric functions or trigonometric functions in one tool.



PK started DQYDJ in 2009 to research and discuss finance and investing and help answer financial questions. He's expanded DQYDJ to build visualizations, calculators, and interactive tools.

PK is in his mid-30s and works and lives in the Bay Area with his wife, two kids, and dog.

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