Depth estimation is an important step to generate 3D structure. The number of algorithm has explored to estimate depth based on Binocular cues (using tw o or more images). But very less work has done to estimate depth from monocular cue (using single image. This paper uses monocular cue as defocus to estimate depth. Also we compare different edge detection algorithms used for depth estimation using monocular defocus cue from single image. The edge detection is an important step in an image processing. The various edge detectors used are Roberts Kernel, Prewitt Kernel, Sobel Kernel, Canny edge detector. The experimental results show that canny edge detector is superior as compared to other and shows better depth for given image.