Cosine Calculator – Calculate cos(x)

Find the cosine of an angle using the cos calculator below. Start by entering the angle in degrees or radians.

How to Find the Cosine of an Angle

In a right triangle, the cosine of angle α, or cos(α), is the ratio between the angle’s adjacent side and the hypotenuse.

illustration of a triangle showing the formula for cosine being equal to side b divided by hypotenuse c

Cosine is one of the three primary trigonometric functions and is abbreviated cos.

You might be asking how to find the cosine of an angle? Use the formula below to calculate cos.

Cosine Formula

The cosine formula is:

cos(α) = adjacent bhypotenuse c

Thus, the cosine of angle α in a right triangle is equal to the adjacent side’s length divided by the hypotenuse.

To solve cos, simply enter the length of the adjacent and hypotenuse and solve.

For example, let’s calculate the cosine of angle α in a triangle with the length of the adjacent side equal to 6 and the hypotenuse equal to 8.

cos(α) = 68
cos(α) = 34

Cosine Graph

If you graph the cosine function for every possible angle, it forms a repeating up/down curve. This is known as a cosine wave.

graph showing a cosine wave

The curve starts with an angle of 0, then decreases to a value of -1 before increasing to a value of 1, and continues indefinitely.

Cosine Table

The table below shows common angles and the cos value for each of them.

Table showing common angles and cosine values for each.
Angle (degrees) Angle (radians) Cosine
0 1
15° π12 √6 + √24
30° π6 √32
45° π4 √22
60° π3 12
75° 12 √6 – √24
90° π2 0
105° 12 √6 – √24
120° 3 12
135° 4 √22
150° 6 √32
165° 11π12 √6 + √24
180° π -1
195° 13π12 √6 + √24
210° 6 √32
225° 4 √22
240° 3 12
255° 17π12 √6 – √24
270° 2 0
285° 19π12 √6 – √24
300° 3 12
315° 4 √22
330° 11π6 √32
345° 23π12 √6 + √24
360° 1

Inverse Cosine and Secant

The inverse of the cosine function is the arccos function. Thus, if you know the cos of an angle, you can use arccos to find the angle.

Secant, on the other hand, is the reciprocal of the cosine value. The following formulas show the relationship between cosine and secant.

cos(α) = adjacenthypotenuse
sec(α) = hypotenuseadjacent = 1cos(α)

You might also be interested in our sine and tangent calculators.