The standard BB forum response is 3 sets of 12 standing calf raises on a Smith machine, twice a week, toes on a block, full range of motion, once a week do the last set to failure at 12 or a couple less. Failure is not being able to raise the heels above horizontal. I've seen a guy do this with 1000 lbs. Those are big calves. I asked the guy if that much weight was necessary. "Got to stimulate 'em." That's a watch-phrase of mine now.