The magnification of an object due to plane mirror is

If m is positive the image is virtual and erect .

If the object is real, the image formed by a plane mirror is virtual, erect, of

i) same size and at the same distance from the mirror.

ii) Magnification of plane mirror is $\text{m}=\frac{\text{size\hspace{0.17em}\hspace{0.17em}of\hspace{0.17em}\hspace{0.17em}the\hspace{0.17em}\hspace{0.17em}image}}{\text{size\hspace{0.17em}\hspace{0.17em}of\hspace{0.17em}\hspace{0.17em}the\hspace{0.17em}\hspace{0.17em}object}}$

or)

 In case of mirror, size of the image is equal to size of the object