How many times have you found yourself standing in a supermarket aisle, trying to figure out which box of cornflakes or bottle of laundry detergent offered the best value?

Sure, the larger one usually gives you more for the money--but not always. And sometimes the smaller one is on sale, which can further confuse the math. 

Free app WhatPrice for iOS lets you compare prices between two items so you can instantly spot the better deal. (Why nothing similar for Android? I searched Google Play high and low, but couldn't find a price-comparison app that seemed decent. If you know of one, by all means tell me about it in the comments section below.) 

All you do is plug in the price and weight (and, if applicable, the number of units) for each item. (You can also substitute length for weight if you're buying something by, say, the foot.) 

In an instant, WhatPrice shows you which one is cheaper, and by what percentage. 

It's literally that simple. However, it would be nice if the app supported more than just two items. What's more, several features require you to pony up 99 cents to unlock the WhatPrice Pro Pack--though what those features are, I can't say. Tapping various areas in the app produces an "upgrade" pop-up, but neglects to mention what the features are that you'll be buying. 

Want something a little more robust? iShop Compare lets you enter up to four items, and converts product quantities between units for the most accurate comparisons. It costs a whopping 99 cents. 

It probably goes without saying that you can accomplish the same basic computations using your smartphone's calculator. But apps like these definitely make that a little easier. If you want to make sure you're getting the best deal on absolutely everything you buy at the grocery store, now you can.

Veteran technology writer Rick Broida is the author of numerous books, blogs, and features. He lends his money-saving expertise to CNET and Savings.com, and also writes for PC World and Wired.

(Source: Savings.com)