At first, I measured out the pellets. But, after some discussion with my vet and doing some research, the pigs really just eat what they need (at least mine do). Overeating is never really a problem with pellets for me. However, I keep up with measuring the amount of fresh veggies to give them and make sure not to give them too much.
I have a satin pig, so I always worry about her weight because she likely has weak bones. Make sure you monitor their weight to be sure they aren't losing/gaining weight than is healthy.