There can be many possible IV's that would produce the Pokemon you have. You are able to narrow down the Pokemon by leveling it up OR evolving it, and submitting the new details to this tool
After your first search, use the "Refine" button instead of "Calculate". Power-up the Pokemon once OR evolve it, observe its new CP HP and Dust Prices, enter the new details, then click "Refine".
The "Refine" process will automatically identify if you evolved the mon (species changed) or if you powered it up and the powered up field is now set to "Yes". But only one at a time. Don't attempt to evolve and powerup between submissions, or powerup multiple times between submissions. The tool assumes you're taking it one step at a time.
Some Pokemon can have their IV's identified immediately, other will require up to 5 Power-Ups to know exactly which IV set it has. Regardless, you should know within 0-1 powerups if it's "close to perfect".