Ya know, the last few times I've made this, I've gone by taste rather than weight.
I'll start with ~3g per gallon and let it sit for ~5 days. If it's not hot enough, I'll add more (including some serranos for a slightly different heat/flavor/aroma) and check it every couple of days until it is where I want it, or even just a bit hotter. A warm, young, uncarbed sample will be hotter than a cold, carbed, aged one.
I'll get around to updating the first post soon to reflect some new information I've learned over the years of making this!