My step-mother was about 167 pounds.
Crabs vary so much in weight that it's impossible to give you a precise answer on that one! They can be monsters like this Tasmanian King Crab at 15lbs...
...or nippers (excuse the pun) like this:
There are so many different types of crab, that I wouldn't even know how to begin giving an average weight for one.
The crabs you can buy at the frozen-fish counter are usually about 200g, though.
For some fascinating photos of the big crab up the top there, I'd recommend reading this article - he was caught by accident, and has been given the (very imaginative) name of Claude. When fully grown, he'll weigh around 30lbs!