Volume conversions are designed to help bakers transition from using cups to scales. While measuring by volume is the norm here in the US, measuring by weight is a more accurate method for ensuring consistent results in cakes, pies and other desserts. One fringe benefit is less mess. For instance, once you memorize the weight of sticky and greasy foods such as peanut butter, corn syrup, honey and shortening, you can weigh them out without messing up a measuring cup. If you think of any more helpful volume to weight conversions, please let me know so I can add them to the list.
Digital Scale Recommendation
Also, if you're looking for a good scale, the one I'm currently using is the Oxo digital scale with pull out display. It's larger than my old scale, but still lightweight and easy to clean.
Volume Conversions
Flour Measurements -- These vary. Sometimes a cup of flour will weigh 125 grams and sometimes 140 grams. It really depends on how it is measured, how much moisture it's absorbed or how it's scooped. Some sources like Cook's Illustrated almost always use 140 grams per cup, while flour companies like King Arthur often use 125 grams. The beauty of using a scale is it doesn't matter! You just go with whatever weight is listed without worrying how the flour was scooped.
Bleached all-purpose flour (1 cup) = 125 grams to 140 grams
Unbleached all-purpose flour or bread flour (1 cup = 140 grams)
Cake flour (1 cup) = 110 grams/4 oz
SIFTED cake flour (1 cup) = 99 grams/3.5 oz
Whole wheat flour (1 cup) = 125 grams (Some brands are courser and heavier)
Raisins (1 cup) = 160 grams
1 cup oats, regular & quick cooking - 81 grams
Granulated Sugar (1 cup) = 200 grams
Light Brown Sugar (1 cup) = 200 grams, but if tightly packed can be 220
Butter (2 sticks or 1 cup) = 228 grams
Shortening (1 cup) = 196 grams
Peanut Butter (1 cup) = 258 grams
Molasses (1 cup) = 337 grams