In the United States, food preparation measurements are expressed in terms of volume: teaspoons, cups, quarts and so forth. But at times you may want to convert volume measurements to weight measurements. Most often this need arises because a recipe uses grams, a metric unit of weight. Occasionally you may also find recipes that use ounces and pounds. Strictly speaking, you cannot convert a volume measure to a weight measure. But you can determine how much 1 cup of a particular item weighs.
Understand the relationship between volume and weight. Volume means the amount of space something occupies. Weight, of course, measures how heavy it is. A dense ingredient has a greater weight in a given volume, such as a cup, than another, less dense ingredient. For example, a cup of water weighs 236 g, a cup of maple syrup 322 g.
Use a conversion chart to determine the number of grams in 1 cup of an ingredient. Conversion charts list the weight in grams or ounces of a cup of many commonly used ingredients. Many cooking websites provide conversion charts. (See Reference 1)
Determine the amount of an ingredient by weight by multiplying the weight in grams for 1 cup by the number of cups you need, expressed as a decimal. For example, if you need 3/4 cup of maple syrup, that's 0.75 cup. To convert to weight measure, multiply 322 g by 0.75. The answer: 241.5 g.
Convert cup measure to pounds. Most conversion charts use metric measurements, but it's easy to convert grams to pounds. Simply divide by 454 (the number of grams in 0.454kg.). For example, the maple syrup in Step 3 equals 241.5 g; divide 241.5 by 454 and you get 0.24kg. To get ounces, multiply the weight in pounds by 16 (for the maple syrup this works out to 241gr).
Create your own conversion chart for ingredients that standard charts don't include. After all, no chart can list all of the thousands of different ingredients people use. Weigh an empty 1-cup container. Carefully fill the cup with the ingredient, then weigh the full cup. Subtract the weight of the empty cup to determine how many grams (or ounces) are in 1 cup. Keep a record of this or make your own chart for future reference.