Unless you have old packaging to compare to, it can be hard to know there’s been a change. Brands rarely advertise that they’re giving you less, especially if the price stayed the same (or went up). Some shoppers might feel the size or weight differences when they lift the familiar-looking packaging. Others remember that their recipe asked for a 15-ounce can…but now that can has 14.5 ounces, instead.

All packaging has to tell you how much you’re getting for your money, but it’s the unit price — usually posted on the shelf — that tells you what you’re paying per ounce, pound, or count. The unit price is one way to comparison shop on the price of things now and vote with your wallet if your usual brand feels, suddenly, very expensive.

The Food and Drug Administration also says that labels on most food packages have to give you the serving size, which can be another clue that something has changed. Are there fewer servings in the container, or is the serving size smaller? If that familiar container now has a change to its servings, chances are there’s less inside.

Besides hitting your wallet, shrinking packaging can increase the frustration factor for many, particularly as Fall leads to a season of cooking, baking, and hosting family and friends. When you’re standing in a crowded grocery store aisle the night before a holiday or gathering, it’s hard to trust your family’s old recipe that calls for a can, bag, or box of something. Combining some up-front investigation of required recipe ingredient amounts with some unit price sleuthing can help protect your wallet…and your blood pressure.