While one cup is 8 ounces by volume, it depends on the ingredient being measured when speaking one cup by weight. Each ingredient weighs a different amount even though they all fill one cup of space, Cathie. Think of feathers and stones- one cup of feathers will weigh quite a bit less than a cup of stones but they both will be one cup. Here's a link to our ingredient weight chart for a list of the weight of the most common baking ingredients. Hope it helps!

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