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 1 lb.). For example, the maple syrup in Step 3 equals 241.5 g; divide 241.5 by 454 and you get 0.53 lbs. To get ounces, multiply the weight in pounds by 16 (for the maple syrup this works out to 8-1/2 oz.).
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.