Strength of schedule is calculated from the opponents projected fantasy points allowed for the WR position. The best rating is +16 which gives the player the advantage against the defense and indicates an easy opponent, the worst rating is -16 which gives the defense the advantage and indicates a tough opponent.
Obviously, bump Welker up your rankings if you’re in a PPR league but don’t expect the type of numbers that he was putting up in New England. For the first time in his career, Welker will be the third best wide receiver option on his own team. Welker will still be productive, just don’t get all nostalgic.