A carpenter laying out a 6/12 roof pitch, a pilot correcting for a crosswind, a game developer rotating a sprite — all of them are computing cosines. The cosine of an angle is the ratio of the adjacent side to the hypotenuse in a right triangle — the horizontal reach of a unit arrow pointing at that angle. Cos(0°) = 1 (pointing straight along the x-axis), cos(90°) = 0 (pointing straight up), cos(180°) = −1.

In coordinates, any point on the unit circle is (cos θ, sin θ), which is why cosine drives rotations in graphics, the horizontal component of forces in physics, and the in-phase part of AC signals. The values repeat every 360°, and the symmetry cos(−θ) = cos(θ) means the sign of the angle never matters. Enter the angle and the calculator returns its cosine — just confirm degree mode first, because cos(60°) = 0.5 while cos(60 radians) is something entirely different.

With the pre-filled defaults — Variable A 10, Variable B 5 — the Cosine Calculator returns Result 50.0000. Change any input and those results update instantly, so you can see exactly how each number you enter moves the answer.