When comparing deals and checking prices you need to be aware of the cost per unit. For example, one brand of diapers has 30 size 4 diapers in its Jumbo pack another has 34 size 4 and in the first brand you will only get 28 diapers if you buy a size 5. Thankfully a lot of stores (like Wal-mart) print the cost per unit right on the shelf tag, but if they don't and when reading ads or deciding how to use your coupons you'll probably want a calculator handy.
Using a calculator is simple all you need to do is type in the price then divide by the units. So, using the first diaper example you find a Jumbo size 4 pack of diapers with 30 diapers at $7.99. The cost per diaper is:
$7.99 / 30 = $.266
A general rule of thumb is that the larger the size package the cheaper the cost per unit. But, be careful using this rule because you can occasionally find a smaller package to be a better deal.
You also need to be careful comparing Wal-mart prices with other store prices. Wal-mart seems to have made some deals with the manufacturers for smaller packages. I recently found a name brand 8 oz. bottle of soy sauce that looked an awful lot like the other stores 10 oz.
Another funny phenomenon is how the use of coupons changes your cost per unit. We love Goldfish at our house and usually buy the big 33.5 oz. package for $6.46 or $.193 per oz. since the smaller 8 oz. package is $2 or $.25 per oz. When we are lucky and find $1/1 coupons I could use my coupon on one 33.5 oz. package to make it $5.46 ($.162 per oz.), but if I chose the 8 oz. package it will be $1 or $.125 per oz. a better deal. This is where having multiple coupons comes in real handy.
Stash a basic calculator in your purse or learn how to use the one on your cell phone so that you are sure of getting the best deal.