To calculate PL and CR for EL use this link:
Note: ignore the difficulty rating on the link as it is geared to D&D3.5 and not Pathfinder
PC's will brease through the encounter quickly and use up very little resources.
(Party Level) or PL
EL (Encounter Level) = PL +2
PC's will move through the encounter with a bit of damage.
PC's will be challenged and definitely take some damage.
EL = PL +4/+5
A player may die or at least be reduced to 0 hp
EL= PL +6
Several players will die or be reduced to 0 hp and possibly need to retreat
When to use which EL's
EL +4 or +5 if multiple encounters in one game session with out resting (estimated 3+ encounters)
EL +6 for just two encounters without resting
EL +8 for just one counter without resting