A round is played on 18 ‘holes’ or target numbers 1 to 18 inclusive.
Only three darts are thrown at each target number.
If the target number is hit in the single area with any of the three darts you have made par, further scoring for the ‘hole’ is as follows:
Any dart hitting the treble area of the target number scores -1 (1 under par), any dart hitting the double area of the target number scores s -2 (2 under par).
The total score for the target number is the score under par for the ‘hole’.
Theoretical maximum is therefore three double target numbers, which is 3 x -2 = -6.
If the target number is missed with all three darts, you receive a penalty stroke, i.e. one over par (+1). Additionally, any dart out of bounds (outside the double ring or on the floor) incurs a further penalty stroke which could total a maximum of 3 additional penalty strokes on any given ‘hole’. A grand total of 4 penalty strokes or 4 over par.
Par is a score of zero.
The worst possible round is therefore 18 x +4 = 72 over par.
Best possible round is 18 x -6 = 106 under par.
NOTE: Only the Double and Treble areas along with penalty strokes alter your score. One, Two or Three darts in the single target area still only equals par. You must hit doubles and trebles to add to your score.