Arccos calculator
Enter a number between −1 and 1 and get the angle whose cosine it is, in degrees or radians. For example cos⁻¹(0.5) = 60°.
Fill in the fields; the answer appears here straight away.
How it's worked out
How it works
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Enter the values
Type the numbers or the formula. Decimals may use a point or a comma. No idea? Click Fill in an example.
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Instant answer
The answer appears as you type, with the most important intermediate values.
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See the working
Under "How it's worked out" you see the steps, handy for checking your own calculation.
What does arccos do?
Arccos (cos⁻¹ or acos) gives the angle that belongs to a cosine. Because several angles have the same cosine (cos 60° = cos 300°), the calculator gives the principal value, between 0° and 180°.
A common use
In a triangle with three known sides, the cosine rule gives the cosine of an angle; arccos then gives the angle itself. Only numbers from −1 to 1 have an arccos. See also the arcsin and arctan calculators.
Frequently asked questions
Is the arccos calculator free?
Yes. The arccos calculator is completely free, with no account, sign-up or usage limit.
How accurate is the result?
The tool calculates with your browser's number precision. For important calculations, always double-check what you entered.
Does it work on my phone?
Yes. The tool works in any modern browser on a phone, tablet or computer.