Weight vs volume for flours

Measure a cup of flour the way you always did it.  Use that weight to calculate the weight of all the flour in your recipe.  Use that weight from now on. Write it on the recipe.  You might find that you need to tinker with the weight a little because measuring with cups will be more variable than by weight.

TomP

When I've taken the time to compare, I find that I usually average 125g/cup of All Purpose or Bread flours.  That's with a fluff, spoon, and level method of filling the cups.

While I haven't done the same with whole wheat or whole rye flours, I still use 125g/cup as the working conversion for translating cups to grams in recipes that only have volume measurements and it usually works out pretty well.  Once in a while, I'll hit an outlier and realize that somebody's Aunt Lavinia scooped the flour into the cups, compacting it in the process and achieving 150-160g/cup.  So I make a note of the difference and add flour to get the same consistency that the recipe describes. 

There are no hard and fast rules on weight to volume conversions, and vice versa, simply because flour is compressible and there isn't a standardized "do it this way or else" method that bakers universally employ.  You make your best estimate and then flex to adjust if necessary.

Paul

It was high time I tried weighing a cup of flour, instead of taking the internet's word for it. Scooped, poked, levelled: 131.6g. I didn't "tap", but I stuck a plastic knife into the flour a few times. That's heavier than most online conversions, but not too out of line.

Anyway, as Tom already said, carry on making the cake as you used to. (I didn't know the University of British Columbia was famous for Ponderosa Cake.) Their recipe conversions are from cups to ml, which is no help whatsoever.

In my kitchen, I’ve found it to be right around 138-140g per cup. Weight can vary with brand, humidity, season …. I stick with 140g and add a bit more liquid if needed.

that volume measurements are deliberately (annoyingly?) non-specific -- & it sort of violates that looseness to try to make them fit our mania for exactitude. My grandmother's chocolate cake recipe called for a cup of flour & a glass of milk. I sat for a long time thinking 'but what size glass' before I allowed myself to bake in her spirit & use as much milk as seemed right. It came out great.

Rob

For flour, a 30% difference between loose vs settled would not be unexpected.  

Just think back to when you had to pour a packet of flour into a storage container...it's almost impossible to get it all into a container the same size as the packet.

Another confounding factor is that not all measuring cups are created equal. I checked several cups I have and one stainless steel and 3 plastic cups all were pretty close to containing 236.6 g of water. However, an old aluminum cup was 241 g.

Also, while the accepted value for 1 cup/8 fluid ounces is 236.6 mL (= g), the FDA value for nutritional labels is 240 mL.

FYI in different countries the standard "cup" can be different!

https://en.wikipedia.org/wiki/Cup_(unit)

1 Canadian cup = 227.3 ml

1 US (customary) cup  = 236.6 ml

1 US (legal) cup = 240 ml, as Alcophile said

1 metric cup = 250 ml

1 old Br Imperial cup = 284.13 ml

I have Anchor Hocking (made in USA) measuring cups. I measured 1 cup of water and then looked at the metric side of the cup. American cup. So, I've been baking in Canada all my life and most likely using American utensits, without knowing it. Guess it hasn't made any difference, but thank goodness for scales and grams.