NEW YORK (AP) — It’s about to get easier to compare prices at some big online stores.

New York’s attorney general says Costco, CVS, FreshDirect, Wal-Mart and Walgreen have agreed to list unit prices on their websites and mobile apps soon.

A unit price tells consumers how much a product costs by each unit of weight. It divides the full price of the item by the size of its packaging. For example, a 16 ounce bottle of shampoo costing $5.99 would have a unit price of 37 cents per ounce. Because the same product can be sold in several different sizes, a unit price is a better way to compare whether a giant box of cereal is really a good deal compared to a smaller one.

Unit prices are already listed in physical stores.