[quote=@Estylwen]
Whyyyy do you knoooow thaaaaat.
[/quote]

Because... bones only typically count for 20-25 pounds of the body weight. SO if you say the average human is 165 pounds and minus 20-25 pounds. Then you have 145-ish pounds. To make burger you need muscle and fat. Healthy humans contain both. Meaning, we would get 145 (1 lbs) burger. 

I know this because I used to play a serial killer cannibal in a dystopian world. His name was Bobo Del Rey. I did a lot of fucked up research for that character.