Radius of curvature
（重定向自Curve radius）
![Radius of curvature and center of curvature](/Images/godic/202501/07/Radius_of_curvature.svg1608.png")
![An ellipse (red) and its evolute (blue). The dots are the vertices of the ellipse, at the points of greatest and least curvature.](/Images/godic/202501/07/Ellipse_evolute.svg1609.png")
In differential geometry, the radius of curvature, R, is the reciprocal of the curvature. For a curve, it equals the radius of the circular arc which best approximates the curve at that point. For surfaces, the radius of curvature is the radius of a circle that best fits a normal section or combinations thereof.