Point spreads are based on power ranking scores.
Example
This week
KANSAS CITY
@
OAKLAND (-8)
Goto power ranking and KC is ranked 13th with 2.9 points in parentheses while Oakland is ranked 4th with a 7.8 score.
Round both digits to neatest whole number so Oakland has 8 and KC had 3.
Find the difference which is 5 and finally the home field team gets +3 which is Oakland to get to 8.
You can do it for every team but the spread maxes at -14 so not to embarrass anyone.
Atlanta goes to Seattle and they have scores rounded to 11(ATL) and -9(SEA) which equals 20 but Seattle in home and gets the +3 so the actual spread is -17.