While not ideal, you can measure dry ingredients in a liquid measuring cup by spooning the ingredient in loosely, then gently leveling it off with the back of a knife or other straight-edged utensil. Avoid packing the ingredient down.
Using a liquid measuring cup for dry ingredients isn't the most accurate method, as liquid measuring cups are designed to measure volume based on the liquid's surface tension, not the settled volume of dry goods. However, if it's your only option, here's how to minimize inaccuracies:
Choose the Right Cup: Select a liquid measuring cup with clear, easy-to-read markings. Glass or clear plastic cups are best.
Spoon the Ingredient: Use a spoon to gently transfer the dry ingredient into the measuring cup. Avoid scooping directly from the container, as this can compress the ingredient and lead to over-measuring.
Fill Loosely: Don't pack or shake the cup. The goal is to have the ingredient settle naturally.
Level Off Carefully: Use the back of a straight-edged utensil, like a knife or spatula, to level off the ingredient at the correct measurement line. Gently sweep away the excess, being careful not to compress the ingredient in the cup.
Double-Check: Look at the measurement line at eye level to ensure accuracy. If you're unsure, it's better to slightly under-measure than over-measure, especially for ingredients like flour.
For very fine ingredients like flour or powdered sugar, sifting the ingredient before measuring can help to aerate it and improve the accuracy of your measurement, even when using a liquid measuring cup.