This is mainly for Pete....what weight do you consider a full cup. I weighted out a cup of water at 234 grams, but I would like to know what you consider the correct weight for a cup of flour. A bag of flour always list the weight of a 1/4 cup as 30 grams, thus a full cup should be 120 grams. Is this the weight you use when you calculate hydration % for someone when they post a recipe. Hand scooping a cup always weights higher than 120 grams.
Unless one knows how a cup of flour is measured out volumetrically, it is very difficult to convert that volume of flour to a weight. There are many different ways that people measure out flour by volume, and in each case the flour will have a different weight when placed on a scale because of the different degrees of compaction. That is why you will often see me ask members how they specifically measured out a quantity of flour by volume. I will also usually ask for the brand of flour if the brand was not specified since all flours do not weigh the same for a given volume. The millers are aware of this issue and have attempted to offer guidance. I can't speak for all millers but as you will note at http://www.gmflour.com/gmflour/ourheritage.aspx,
prior to October, 1989, General Mills advocated the use of the "dip & level" method of measuring flour. However, beginning in October of 1989, General Mills started to recommend the "spoon & level" method to ensure more accurate measuring by avoiding packing too much flour in the measuring cup. The recommendation appears on flour packages, but not on individual recipes. The General Mills method is the one that we refer to on the forum as the "Textbook" method. I believe that King Arthur also recommends the Textbook method.
If in a given case a member tells me how he or she measured out a given volume of flour, and the brand as well, I usually go to the Mass-Volume Conversion Calculator at http://foodsim.toastguard.com/.
Then, based on the information provided, I use that tool as best I can to convert the volume of flour to a weight based on the way that the flour was measured out. That tool was devised by member November and it was based on November and I having conducted literally hundreds of conversions of volumes of different types and brands of flour (the ones that he and I had access to at the time) to weights using different measuring methods and different measuring cup sizes (e.g., one cup, 1/2 cup, 1/4 cup, etc.). November used these measurements to come up with the algorithm for the tool. You will note that one of the flour Measurement Methods in that tool is the "Textbook" method. That is the same as the method now recommended by General Mills. If a particular brand of flour is not in the pull-down table in the tool, I use the closest flour as a proxy (e.g., I will use the King Arthur bread flour for another brand of bread flour not in the pull-down menu).
If, for some reason, the tool can't be used at all (e.g., the type and brand of flour are not in the pull-down menu), I will arbitrarily use a weight based on the Textbook method for the type of flour in question (e.g., all-purpose, bread, high-gluten). But, whatever weight value I come up with, whether using the tool or otherwise, I will do a few calculations to see how the weight value affects the hydration calculation for the dough recipe in question. If the hydration value is considerably higher or lower than the rated absorption value for the type of flour used, I will note that to the member as a possible red flag and I am likely to suggest to the member that he or she may have to make adjustments to the amount of water and/or flour to get the desired finished dough condition. That is really the only option I can suggest since I have no way of knowing what hydration the member was using or intended. Also, members sometimes don't remember exactly how they measured out a quantity of flour. And the members often use different types and shapes of measuring cups (and measuring spoons as well).
I think you can see how many problems can be presented when using volume measurements. I have seen instances where conversions I conducted on behalf of a member did not produce the desired results. Invariably, I do not have an explanation for why the results were not what the member was looking for. I think that is why many members end up buying digital scales.
EDIT (4/3/14): For the Wayback Machine version of the above GM link, see http://web.archive.org/web/20100105084108/http://www.gmflour.com/gmflour/ourheritage.aspx