Enter a value between −1 and 1 to find the angle whose cosine equals it.
How to Use the Inverse Cosine Calculator
Enter a value between −1 and 1. The angle whose cosine equals that value comes out in degrees or radians, whichever is selected.
θ = cos⁻¹(x), for −1 ≤ x ≤ 1"Inverse cosine" and "arccosine" name the exact same function — cos⁻¹ is just the more common notation in calculus and engineering contexts, while "arccos" shows up more in programming languages and calculators. Whichever name is used, it always returns a value between 0° and 180° (or 0 and π radians), by convention, even though cosine itself repeats that same output for infinitely many angles.