Posting this here if someone else needs it.
How to Use a Damage Calculator
This is the best damage calculator (for now).
1) Open up Shoddy Battle's Team Builder and enter the EVs for the Pokemon you want to use for the damage calculation in order to find their stats. Alternatively, you can use a
Stat Calculator.
2) Enter the stats for the Attack, Defense, and HP fields.
3) Enter the base power of the move before STAB.
4) Select the type effectiveness of the move on the left hand side.
5) If the Pokemon receives STAB on the move, select Yes from the STAB field.
6) If the Pokemon is holding an item (for example, Life Orb), select it from the "Offensive Item" list.
7) If the Pokemon is weak to Stealth Rock, select x2, if it is resistant, select x.5 from the Stealth Rock field.
8) Click Calculate damage.
9) The damage dealt and the potential for OHKOs and 2HKOs is displayed at the bottom of the calculator.
Reference Image: 216 SpA Mild Salamence @ Life Orb using Draco Meteor against 252 HP / 0 SpD Relaxed Swampert