Calculate the cosine of an angle, or find the angle from a known cosine value.
How to Use the Cosine Calculator
Works both directions the same way the Sine calculator does — toggle between solving for the value or for the angle.
Cosine is sine's mirror image, offset by a quarter turn: cos(θ) = sin(90° − θ). Where sine tracks the opposite side over the hypotenuse, cosine tracks the adjacent side over the hypotenuse —
cos(θ) = adjacent ÷ hypotenuse— and this Cosine Calculator runs it either direction: angle to ratio, or ratio back to angle via arccos. Same bound as sine applies here too, since an adjacent side can't outgrow its hypotenuse either — cosine stays between −1 and 1, always.
Degrees or radians changes the answer, not just the label, so set the angle mode to match whatever you're working from before trusting the number.