Magnification $\text{m}=\frac{\text{size\hspace{0.17em}of\hspace{0.17em}image}}{\text{size\hspace{0.17em}of\hspace{0.17em}object}}$.  If m is +ve, the image is

In magnification the  sign’s are not for the image form the lens. According to sign convention, the heights measured perpendicular to the x – axis above the positive and heights measured to the x – axis below are negative. Virtual image have the magnification as positive they are erect and on the x – axis where as real image have the magnification as negative since the image formed is laterally inverted and are below the x – axis. So virtual images will be positive and real images will be negative