this is the simplest IV calculator I have found yet.
It is almost impossible to know all,
but it is possible for the highest IV you have.
for example, if you used the calculator and you got 30-31 on attack.
and if your pokemon has "likes to thrash about", it means it has 31IV.
Also, there is a judge since gen3 which tells you about pokemon's highest IV stat
if he says...
"It has highest attack (or something like that...) It can't be better than this",
it means it has 31IV
He's at battle tower in gen4 and at Battle Subway in gen5
this is also helpful to know how the judge judges the pokemon's IV