diff --git a/src/ol/geom/Polygon.js b/src/ol/geom/Polygon.js
index <HASH>..<HASH> 100644
--- a/src/ol/geom/Polygon.js
+++ b/src/ol/geom/Polygon.js
@@ -413,7 +413,7 @@ export default Polygon;
  * Create an approximation of a circle on the surface of a sphere.
  * @param {import("../coordinate.js").Coordinate} center Center (`[lon, lat]` in degrees).
  * @param {number} radius The great-circle distance from the center to
- *     the polygon vertices.
+ *     the polygon vertices in meters.
  * @param {number=} opt_n Optional number of vertices for the resulting
  *     polygon. Default is `32`.
  * @param {number=} opt_sphereRadius Optional radius for the sphere (defaults to
Mention unit of radius for Polygon.circular()

Radius was using an unknown unit. This makes it clear that it will be interpreted as meters.