On the label, all purpose flour supposedly weighs about 30g for 1/4 cup, or 120g per cup.
However, when I weigh mine, I always get more like 150g per cup. (Using King Arthur AP flour.) That's a full 25% more weight per cup of flour than it's supposed to be.
I know that many factors can affect the density of flour, but this still seems like an abnormally large difference.
Personally when I am baking I would rather follow weight measures, when they are given, but given that the supposed 'equivalence' is so off (and most American recipes are tested for volume measurements) I'm really not sure what's optimal.
Sometimes I would also like to substitute cake flour for AP, and I know that weights are more reliable than volumes for that. So I feel like I need to modify the recipe for the 'wrong' weight and then base my substitution off of that.
I'm not exactly sure what my question is...other than that I'm a bit frustrated. But has anyone else had the same experience? Are the standard equivalences just wrong?