While the amount of flour in a 5-lb. bag varies, a bag of King Arthur brand all-purpose flour consists of about 18 to 19 cups of flour. The number of cups within bags of flour depends on the flour's density and type.
When a recipe calls for one pound of flour, consider the type of flour before measuring how many cups to add. When the recipe calls for:
- All-purpose flour - use 3 1/3 cups
- Cake flour - use 4 1/2 cups
- Pastry flour - use 4 1/4 cups
- Whole wheat flour - use 3 1/3 cups
When measuring the flour, it is also important to note whether the recipe calls for sifted or unsifted flour, as well as how it is listed in the recipe. For example, a recipe that calls for "1 cup flour, sifted," means to first measure 1 cup of flour, and then sift it. If a recipe calls for "1 cup sifted flour," it means to sift the flour first, and then measure it to 1 cup.
The protein level within the flour also affects its density and weight, which is an important consideration when substituting flours in recipes. For example, using bread flour in a recipe that calls for all-purpose flour can result in a denser bread with a heavier texture. For best results, it is advisable to use the flour specified in the recipe.