Calculating IVs accurately. is it possible?

So I want a Volcarona with Hidden Power(Rock) I was going to give it HP(grass) but I think teaching it Giga drain and HP(rock) is a better option. anyhow.. for HP(rock) I need:

(hp, att, def, sp. at, sp. def, sp)x/x/x/31/30/30 - the problem is every calculator I use gives me ranges (29-30) I need to know if it’s 29, or 30. if it’s 29 I’ll release the pkmn. but if it’s 30, I can move on to the next stage.

I know if I bring the Pokemon to level 100 I can tell once and for all. but I don’t have rarecandy like that, and I’m not about to spend 3 days training a Pokemon only to find out the IVs weren’t what I needed it to be.

So PLEASE someone tell me how to measure this accurately. I’ll provide with information as to what I’m doing, and how I’m calculating this:

Im not sure if this site has an IV calc, but I googled it and I’ve been using the one in serebii, psypoke tool & marriland. I input ALL information (even optional information) in the calculator(s).

I bring the pkmn from level 1, to 20. noting ALL EVs gained. SO I can input this info on the calculator and get (to my understanding) an accurate reading. Yet I keep getting ranges..

someone help :(

Pleaselog inorregisterto add a comment.

So to have HP rock, at Lv. 35 (the level you catch it) it needs to have:

Speed inducing nature that lowers Atk or Def(Hasty, Timid): X/X/X/110/89/93

SpA inducing nature that lowers Atk or Def(Modest, Mild): X/X/X/129/89/85

SpD inducing nature that lowers Atk or Def(Calm, Lax): X/X/X/110/97/85

Those are the optimum nature but with a neutral nature it will be(Lonely,Bold,Hardy, Docile, Bashful, Quirky, Serious) : X/X/X/110/89/85