A radius is a straight line from the center to the boundary of a geometric object, especially a circle, sphere, or disk. Radius may also refer to:
- Any of several concepts closely related to the above, including
- Radius of curvature, a measure of curvature in advanced mathematics
- Radius, a measure of the curvature of a stringed instrument's fingerboard
- Bend radius or minimum bend radius, the minimum radius one can bend a pipe, tube, sheet, cable or hose without damage
- Radius of curvature, a measure of curvature in advanced mathematics
- Radius (bone), one of the two bones in a forearm
- RADIUS, a network authentication protocol
- Radius (Chrono Cross), a character from the role playing game Chrono Cross
- Radius (computer), a computer hardware firm
- Radius (Reporting), a Reporting tool for Office users.
