This formula scales to any group size. Always use the party's actual total HP and actions.
To judge encounter difficulty, follow these steps to assess Easy, Challenging, Hard, or Deadly.
Step 1: HP Baseline
Add up monster encounter total HP.
Add up who party HP.
Monster HP ≈ ½ party HP = Easy
Monster HP ≈ equal party HP = Challenging
Monster HP ≈ 1.5× party HP = Hard
Monster HP ≈ 2×+ party HP = Deadly
Step 2: Action Check
Drop 1 step when Monsters has fewer actions than party's total.
Raise 1 step if Monsters has more actions (multiattacks) per round than party's total.
Step 3: Spice Bump
Raise 1 step if monsters have strong control, resistances, flight/range, or other tactical edge.
Drop 1 step if they're fragile, with no defenses or tricks.
Note: Encounter difficulty primarily measures combat duration and party exposure time. Remember that fragile classes (Wizards, Thieves) remain vulnerable to focused attacks and critical hits regardless of encounter rating.
Open Dungeons provides a digital tool: Monster Encounter Calculator
