Just because something costs a dollar doesn’t necessarily make it a deal. Bankrate.com urges people to do some simple math and comparison shopping before making a habit of buying certain items at the dollar store. Often times, it may be cheaper to buy things that last a while in bulk from warehouse stores or other discount stores.

When trying to determine what the better deal for a product is, divide the price by the number of items you’re getting. For example, 45 foam cups from the dollar store may cost a dollar, but you may be able to get 1,000 foam cups for $12.18 at a warehouse. At the warehouse price, you’d be paying about $.01 a cup, whereas you’d be paying $.02 a cup at the dollar store. Since foam cups last for a long time, why not stock up and pay less?

Here are some items that Bankrate.com found that tend not to be deals at the dollar store:

• Bottled Water
• Sugar Substitutes
• One-ply Napkins
• Foam Plates
• Dish Soap
• Toothpaste
• Batteries

The dollar store can be a place of great savings, but just be sure to do some comparison shopping before you decide where to get certain items.

Head over to 10 dollar-store duds for the full video.