An exact answer may be impossible but here is some math to suggest the closest possible estimation.
First lets compare by arm length
Henry Cavill is 6'1" via his imdb page. So given the length of his body in pixels to the length of doomsday's arm in pixels we have:
D = Doom:510px
S = Superman:342px
C = Cavill Ht in Inches: 73
S/C = 4.698 pixels per ...