Hi. Is there any difference between dry and liquid measuring cups? Do they measure the same amount, and if so, why do I need both? I had heard once that there is a difference between the volume of dry and liquid measures.--Bob
The volume measured by dry and liquid measuring cups typically used in the kitchen is the same. To be clear, I am using the word "cup" here to mean the container and not necessarily the unit of measure, so the same holds true for measuring a half cup, or quarter cup, using the appropriate sized measure.
The reason for having two sets is because dry ingredients are easiest handled using a "scoop and level" technique where the cup is overfilled and then a knife or other straight edge is scraped across the top to level the amount to the right measure. This only works if the measuring cup is filled to the brim. If you try to measure a cup of, say, sugar using a liquid measuring cup you can't scoop and level, and it is harder to get an accurate measure by using the line. Dry ingredients don't want to make a nice straight line across their top and if you try to get them to, they settle in the cup causing error, so the cup used for liquid measures is not accurate for dry ingredients.
Conversely, it is difficult to measure liquid if you need to fill the measuring cup to the very brim, and even if you succeed, you either make a mess or have difficulty getting the entire amount transported to the next step, so dry measuring cups are not easy to work with for liquid ingredients.
In the U.S., the quantity measured by dry and liquid measured less than a pint are the same. After that, there is a difference. A U.S. pint used for liquid measures is 473 milliliters, where as a dry measure pint is 551 milliliters, which means it is 16.5% larger. A U.S. dry measure quart is 16.4% bigger than its liquid counterpart, at 1101 milliliters vs. 946.