Out of toilet paper so soon? Who the heck ate all of the Haagen Dazs? Why is this grilled cheese sandwich less cheesy than before?

Complaints like these – household staples getting used up faster; food not lasting as long -- are becoming more common.

No, members of your household aren't being wasteful or taking extra helpings of dessert. Those boxes of pasta, rolls of paper towels, jars of pesto and packages of hot dogs really are getting smaller. But manufacturers hope that you haven't noticed.

Same look, less filling!
A recent Consumer Reports investigation found that the amount of dish detergent, toilet tissue, and first aid spray in those same old containers has shrunk as much as 20%.

Slimmer pickings at the supermarket

Product

Old size

New size

Difference

Tropicana orange juice 64 oz. 59 oz. (7.8%)
Ivory dish detergent 30 oz. 24 oz. (20%)
Kraft American cheese 24 slices 22 slices (8.3%)
Kirkland Signature paper towels 96.2 sq. ft. 85 sq. ft. (11.6%)
Haagen Dazs ice cream 16oz. 14 oz. (12.5%)
Scott toilet tissue 115.2 sq. fit. 104.8 sq. ft. (9%)
Lanacane first aid spray 113 grams 99 grams (12.4%)
Chicken of the Sea salmon 3 oz. 2.6 oz. (13.3%)
Classico pesto 10 oz. 8.1 oz. (19%)
Hebrew National franks 12 oz. 11 oz. (8.3%)

Source: ConsumerReports.org

Blame it on the rising costs of producing these goods, such as raw materials, energy, and facility costs, say manufacturers. As their expenses rise, they've got to find ways to make up the difference: Either charge more for the product, or give less of it to you for the same money.

The latter strategy -- charging the same amount for less-generous servings -- is the safer bet: Studies show that shoppers are more sensitive to price increases than product volume decreases. And manufacturers go to great lengths to get you to overlook the downsized items in your shopping cart.

Packaging tricks that throw you off the scent
Getting you to overlook the fact that there's one-fifth less detergent in that Ivory bottle is all about subtle tweaks in presentation. To disguise downsizing, manufacturers do everything from indenting the bottom of the container to whipping pockets of air into the same old ice cream container.

As I pointed out in "5 Mind Games Stores Use to Make You Spend," be particularly wary if a company comes out with a new container that is taller than the previous version – a taller, skinnier Tropicana carton, for example. It's a classic bit of visual trickery at work: We tend to notice changes in height more than changes in girth.

It's unlikely that the downsizing trend will be reversed. Your best strategy is to pay attention to per-unit pricing – the real measure of how much you're paying for the actual product, rather than the new packaging.

More ways to save on everything on your shopping list:

Fool.com columnist Dayana Yochim is able to calculate the per-unit price on any item in less than 30 seconds. If only they gave medals for that. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.