need some help

[Beaufighter]

can any body tell me how to figure out the prop size on my 1977 140hp johnson outboard motor would be.
lost the prop in the lake when it spun off the motor,and now have know idea as to what the size was and the pitch is.
hope that i do not have to pull the boat out of the lake but if i do thats going to be a fun job with no prop
thanks every body

[boats.net]

There are no specific ways to tell prop sizes, only trial and error.