Cosine Calculator

About this calculator

Cosine is one of the three core trigonometric ratios: in a right triangle it is the length of the side adjacent to an angle divided by the hypotenuse. On the unit circle, cos(θ) is simply the x-coordinate of the point you reach after rotating θ degrees from the positive x-axis, which is why cosine values always stay between -1 and 1 and repeat every 360°. cos(0°) = 1, cos(90°) = 0, and cos(180°) = -1 are the anchor points most people remember from trigonometry class.

Beyond the classroom, cosine shows up wherever a quantity depends on the angle between two directions. Physicists use it in work and power formulas (W = F·d·cos θ), electrical engineers use it for AC power factor calculations, and 3D graphics programmers use it constantly to rotate objects and compute lighting via dot products. Surveyors and navigators rely on cosine (often through the law of cosines) to resolve triangles when only sides and one angle are known.

This calculator takes an angle in degrees and returns its cosine directly — the inverse operation, finding the angle from a known cosine value, is what an arccos calculator does instead.