Article four in a 10-part series

Ladies, all players wear uniforms [jerseys] with numbers, so learning the numbering system will make it much easier to follow what’s happening on the field, therefore taking another step in fully understanding the great game of football. 

The NFL adopted a jersey-numbering system in 1973 where each position corresponds to a range of numbers.  

Covering the full range 1 to 99, the numbers are displayed on both the front and back of the jersey, on both shoulders, and often on the helmet.  The numbers worn on the sleeve or shoulder are known as "TV numbers" so the TV analyst can quickly identify the player for the broadcast. 

Below is the numbering system the NFL has used since 1973:

1 - 19 are worn by quarterbacks, kickers, and punters. Since 2004, wide receivers are also allowed to wear numbers between 10 and 19 if they choose, even if a number from 80 through 89 is available.

20 - 49 are worn by running backs, tight ends (40-49, when an 80-89 number is unavailable), cornerbacks and safeties.

50 - 59 are worn by linebackers, defensive linemen and offensive linemen.

60 - 79 are worn by members of both the offensive line (the tackles, guards and centers) and defensive line (the defensive ends, defensive tackles or nose guard).

80 - 89 are worn by wide receivers and tight ends.

90 - 99 are worn by linebackers and defensive linemen.  

0 - 00 are no longer used, though they were issued in the NFL before the number standardization in 1973.

The NFL numbering system is based on a player's primary position. If a player changes primary positions during his career, he does not usually have to change his number unless he changes from an eligible receiver to ineligible or vice versa. 

In preseason games, when teams have expanded rosters, players may wear numbers that are outside of the above rules. When the final 53-player roster is established, they are reissued numbers within the guidelines.

Players have often asked the NFL for an exception to the numbering system rule. In 2006, New Orleans Saints running back Reggie Bush requested to keep the number 5 he wore in college. His request was declined, and he was assigned number 25 by the team.  Former Seattle Seahawks linebacker Brian Bosworth wore number #44 in college for the University of Oklahoma and wore that number during the 1987 preseason with the Seahawks. He took the NFL to court for the right to wear #44, but he lost and had to switch to #55.

So now I hope you have a better understanding of the NFL numbering system for uniform jerseys. 

Source: Wikipedia