Cameras with rolling shutters (RSs) dominate consumer markets but are subject to distortions when capturing motion. Many methods have been proposed to mitigate RS distortions for applications such as vision-aided odometry and three-dimensional (3D) reconstruction. They usually need known line delay d between successive image rows. To calibrate d, several methods have been proposed that often involve complex procedures. This Letter proposes an easy RS calibration method by using an off-the-shelf light-emitting diode (LED) panel, using the fact that the RS causes the blinking LED columns to appear slanted in images by a static camera. The calibration starts with extracting the LED lights and then rectifies the images to remove the lens distortion and misalignment between the camera and the LED panel. Next, blocks of slanted bright LEDs are recognized and their inclination leads to the line delay estimate. Our method needs not to move the camera, adjust the ambient light, or calibrate camera intrinsic parameters beforehand, and it can usually estimate the line delay given two LED panel images in one second. Extensive tests with industrial cameras and consumer cameras of wide-angle and fish-eye lenses validate its competitive accuracy relative to the established methods.