Calculate the arccosine (inverse cosine) of a value and return the angle in degrees and radians with exact fractions of pi.
Share this calculator
Result
The angle whose cosine equals 1.
Also in Functions
Trigonometry
The arccos calculator finds the angle whose cosine equals a given value. Enter any number between -1 and 1 to get the angle in both degrees and radians, with exact fractions of pi for common values.
Arccosine (cos⁻¹ or acos) is the inverse of the cosine function. If cos(60°) = 0.5, then arccos(0.5) = 60°. The result is always in the range 0° to 180° (0 to pi radians).
The domain of arccosine is [-1, 1]. Values outside this range have no real solution.
Arccosine returns only the principal value in [0°, 180°]. Other angles with the same cosine (e.g. -60° also has cos = 0.5) are not shown.
Frequently asked questions
90 degrees (pi/2 radians). cos(90°) = 0, so arccos(0) = 90°.
Arccos is the inverse function: it returns an angle from a cosine ratio. Secant (sec) is the reciprocal: sec(x) = 1/cos(x).
Related
These related calculators come from the same leaf category, nearby sibling categories, or the same top-level topic.
Calculate the arcsine (inverse sine) of a value and return the angle in degrees and radians with exact fractions of pi.
Calculate the arctangent (inverse tangent) of any real number and return the angle in degrees and radians.
Calculate the cosine of an angle in degrees or radians with exact values for common angles.
Calculate the sine of an angle in degrees or radians with exact values for common angles like 30, 45, and 60 degrees.
