Cosine Calculator

How it is calculated

The angle is read in degrees. The tool converts it to radians with θrad = θdeg × π ÷ 180 and then evaluates cos(θrad). The answer is a pure ratio with no unit, shown to 6 decimal places. Any real angle is accepted, including negative angles and angles above 360°, because cosine repeats every 360°: cos(θ) = cos(θ + 360°) and cos(−θ) = cos(θ). The result always lies between −1 and 1. An empty box gives no result. Exact values such as cos 90° print as 0.000000 because of the rounding to six places, not because the floating-point result is exactly zero.

Common mistakes

• Typing radians into a box that expects degrees. Entering 1.5708 for a right angle gives cos of 1.5708 degrees, about 0.999624, not 0.
• Expecting an exact zero at 90° or 270°. The display shows 0.000000, which is a rounded value; do not use it as a proof of exact perpendicularity.
• Assuming a negative angle gives a negative cosine. Cosine is even, so cos(−60°) is 0.5, the same as cos(60°).
• Using the cosine when you actually have the ratio and want the angle. For that direction you need the arccosine, not this tool.
• Confusing cosine with sine. At 30° the cosine is 0.866 and the sine is 0.5; they swap at 60°, so check which ratio your triangle problem calls for.