Our recipes list 1 cup of flour as weighing 5 ounces, but different sources may list a cup of flour as weighing slightly more or less. What causes this discrepancy?
The weight of a cup of flour depends on how it is measured. In the test kitchen, we favor the dip-and-sweep method—we dip a measuring cup into a container of flour and then level the flour with a straight edge—but some bakers prefer to spoon flour directly into the cup. Since these techniques—along with the heavy- or light-handedness of the baker—incorporate different amounts of air, we’ve found that there can be up to a 20 percent difference in the weight of a cup of flour, a variance that can easily ruin a recipe. To determine our standard weight for flour, we had dozens of volunteers measure out 1 cup, weighed the results, and took the average (5 ounces) as our standard.
THE BOTTOM LINE: We provide volume measurements for readers who don’t have access to a food scale, but measuring by weight is the only way to guarantee accuracy. If you have a food scale and a weight measurement is provided in a recipe, ignore the volume measurement. And since weighing standards vary depending on the recipe author, do not be tempted to transfer the weight conventions from one recipe to another.