Quarterback Passer Rating

Passer rating is a measure of the performance of quarterbacks or any other passers in the NFL. There are at least two formulae currently in use: one officially used by the National Football League and the Canadian Football League, and one used in college football.
The Passer Rating is calculated from four components using each quarterback’s (1) completion percentage, (2) passing yardage, (3) touchdowns and (4) interceptions . The NFL’s current “passer rating” or “quarterback rating” system (the former term being the official one) was conceived by Pro Football Hall of Fame’s Don Smith in 1973. The rating was applied retroactively to all previous seasons. The system is of a sliding-scale design, where outstanding performances meet diminishing returns faster than sub-par ones. The best passer rating that a quarterback can obtain under it is 158.3 (technically 158.333→), while the worst is zero. Conceptually, the average rating would be 79.2 (technically 79.166→), since this is equidistant between zero and 158.3, but the architects of the rating had 66.66→ in mind as the “average” score (100 * [1.00*4]/6).

Cumulative League-wide Average
The cumulative league-wide average passer rating for the years 2000 through 2003, all inclusive, was 78.9 (the figure is typically rounded to the nearest 1/10 of a point); however in 2004 the league average was 82.8, the highest ever recorded. This may be due, at least in part, to stricter rules regarding pass interference.

Details on Components and Formulae

C = Completion Percentage

((Completions/Attempts) x 100 – 30)/20

Y = Passing Yardage or Yards per Attempts

(Yards/Attempts) – 3) x .25

T = Touchdowns per Attempts

(Touchdowns/Attempts) x 20

I = Interceptions per Attempt

2.375 – (Interceptions/Attempts) x 25

The four components are combined in the following formula:

((C + Y + T + I) / 6) x 100

See also FitnessMath.com NFL Quarterback Passer Rating