I dunno. Been making this one for decades based on taste. Sometimes peppers are hot, sometimes they aren't. Had times where two red jalapenos will light this stuff up, other times, 15 seranos barely put a dent in it. Onions, some are potent, some aren't. and so on...
My best guess numbers:
8-10 roma tomatoes. Try to avoid the flavorless waterballs
a baseball sized white onion. (or yellow, it really doesn't matter that much)
5-6 seranos
a half cup of chopped cilantro leaves (a medium sized bundle)
one or two limes
1/2 tsp ground cumin (if your spices are old, then you are going to need a lot more)
You can also use a few bundles of long green onions rather than globe shaped white or yellow.
You can use habaneros if you prefer.
Or white vinegar rather than limes if you can't get them (there is a major taste difference here)
You can roast the peppers and tomatoes if you want.
Sh!t, you can even cube up a mango and toss it in if you want.
This salsa is a concept that you need to adapt to your tastes, rather than looking at it as a strict recipe.