Standard weight conversions for converting cups of flour to grams of flour?
There is no official standard.  The USDA uses 125g/cup, but labels on packages claim different weights for one cup:


Gold Medal brand: 130g
King Arthur brand: 120g (updated 2016)
wolframalpha: 137g
superpacked: 165g


I always convert my recipes to weights using 140g/cup.