You no longer have to wonder why your grill is running out of gas a bit sooner than it used to.

Following the lead of ice cream makers who decided consumers would rather pay the same and get less, the propane exchanges you're getting at places including The Home Depot and Lowes are selling you less gas in your tank but are charging you the same.

What had once been 20-pound tanks (which could actually only be filled to 18 pounds) are now 15-pounders, according to the AP. The punier tanks came as a surprise to consumers who hadn't noticed the unadvertised shrinkage.

The idea of shrinking the volume of propane came up last year when gas prices soared to new heights. Rather than jack up the propane tank prices, the companies put in less fuel. But as prices dropped, the amount of propane remained at its new, smaller level.

Translation: Good for the companies, bad for you.

Two of the major tank exchange companies, Blue Rhino and Amerigas, have been filling only to 15 pounds for a year, a Blue Rhino spokesman confirmed to the AP. The Home Depot said it hadn't heard complaints from its customers. Perhaps that's because, until now, its customers didn't know.

It typically costs $20-$25 to exchange an empty tank for a full one, or as little as about $14 to refill one at membership stores such as a BJs Wholesale Club.