mdn
atan2() calculation always returns an <angle> in degrees, not radians
MDN URL
https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Values/atan2
What specific section or headline is this issue about?
The introduction (and possibly other sections of page).
What information was incorrect, unhelpful, or incomplete?
I might be misunderstanding here, but it mentions.
The function accepts two arguments and returns the number of radians representing an
between -180deg and 180deg.
I've tested this, and wouldn't this actually be the number of degrees between -180deg and 180deg? For example, applying a radians-to-degress conversion via:
--angle-rad: atan2(3, 2);
--angle-deg: calc(var(--angle-rad) * 180 / pi);
would end up with a wildly incorrect result for --angle-deg.
In this example, I'd used CSS trigonmetry calculations to offset a gradient based off the position of the mouse relative to the centre of the screen: https://codepen.io/Jollus/pen/WbweZoX
We can see in JS angle rad in the top-left what the radians is expected to be, calculated with JavaScript. However, this is not what ends up being applied to the --angle (the CSS calculation).
To me, it seems clear that atan2() is returning the result in degrees, and not radians. This may be so for other trigonometry calculations as well, although I've not tested those.
What did you expect to see?
I would think that any reference to atan2() returning radians would need to be updated to show that it returns degrees instead, unless there's something I'm missing here.
Do you have any supporting links, references, or citations?
https://codepen.io/Jollus/pen/WbweZoX
Do you have anything more you want to share?
No response
MDN metadata
Page report details
- Folder:
en-us/web/css/reference/values/atan2 - MDN URL: https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Values/atan2
- GitHub URL: https://github.com/mdn/content/blob/main/files/en-us/web/css/reference/values/atan2/index.md
- Last commit: https://github.com/mdn/content/commit/85fccefc8066bd49af4ddafc12c77f35265c7e2d
- Document last modified: 2025-11-07T15:58:06.000Z
Hello, angles don't have the concept of units. An angle is just an abstract mathematical entity and you can measure it in any unit. However I agree that mixing "radians" and "degrees" in the same sentence is confusing, and we can just change it to "returns an <angle> between -180deg and 180deg".
Hi! I'd like to work on this issue.
I will update the documentation to clarify that atan2() returns an
Thanks for that. It would also be worth checking these pages:
- https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Values/atan
- https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Values/asin
- https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Values/acos
These also contain a similar line, resembling:
The function contains a single calculation that returns the number of radians representing an angle between 0deg and 180deg.
By extension, these pages also reference radians in their descriptions.
- https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Values/sin
- https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Values/cos
- https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Values/tan
They are phrased as:
The function contains a single calculation that must resolve to either a number or an angle by interpreting the result of the argument as radians.
Personally, I find the phrasing in the latter to be less confusing, since they mention that an angle is interpreted, rather than represented (interpreted implies some sort of calculation or conversion, which is what happens). Maybe those ones could be left alone.
Hi! I can work on updating the related CSS math function pages (atan(), asin(), acos()) to clarify angle wording and avoid mixing radians/degrees terminology, similar to the atan2() fix.
Hi, I’d like to work on this issue. Please assign it to me if it’s still available. Thanks!
