Find the angle whose sine, cosine, or tangent you know. Enter the value, function, and output unit.
Usage Tip
Use inverse tangent on rise over run to get the angle of a slope or ramp.
asin and acos require an input from −1 to 1
They are essential for finding angles in triangles from side ratios.
Inverse tangent accepts any real number.
Choose degrees or radians for the output.
Inverse trigonometric functions work backward from a ratio to an angle. If the sine of an angle is 0.5, the inverse sine returns 30 degrees. The same applies to cosine and tangent. The input to inverse sine and inverse cosine must be between minus 1 and 1, since no angle has a sine or cosine outside that range, while inverse tangent accepts any value.
Each function returns a principal value in a limited range: inverse sine and inverse tangent give angles between minus 90 and 90 degrees, and inverse cosine gives angles between 0 and 180 degrees. Other angles with the same ratio exist, so you may need to adjust for the quadrant. Pick the output unit carefully, since a result in radians looks very different from the same angle in degrees.