The Hercules is the world's biggest moth and can grow up to a wingspan of 27cm. The female is generally larger than the male - and this is quite a small male!
This old photo (not to scale) is of a female, so you can see the difference in shape. An interesting fact is that the female lives for such a short time that she is actually born without a mouth.
(I won't repeat Peter's comments about females without mouths!!!!)