First, there's a tape measure that you can by to measure the pigs and give you an approximation as to their weight. There's also a formukaf you can use and measure them with a standard tape measure and calculate the weight. Of
course this is assuming that the pig will stand still and let you put the tape around them. I don't recall the formula, but searching the Internet might turn it up.
A pig can be slaughtered at any size you want. I've even done them early for use on a spit or as luau piglets. Or I can wait for them to get about 6 months old for bigger chops and roasts. Or even wait until they are 1-2 years old for bigger yet.
My four criteria for determining when I slaughter a pig...
...it's filled out nicely and not skinny.
...it's got to be a size that I can handle it by myself.
...there has got to be room in the freezer.
...and if
local food sources run out, such as during a drought year, then the pigs go into the freezer. I don't wish to buy expensive commercial
feed just to grow the pigs bigger.