Linear Magnification ($m$) is the ratio of image height ($h^{\prime }$) to object height ($h$).

• For a lens: $m=\frac{h^{\prime }}{h}=\frac{v}{u}$
• For a mirror: $m=-\frac{v}{u}$
• If $m$ is positive, the image is virtual and erect.
• If $m$ is negative, the image is real and inverted.