There are really no hard fast rules about what is cheapest. One week it might be the store brand value pack and the next week a smaller sized name brand might be on sale. Checking to see if something is the best deal ounce for ounce can save you an extra $2-$5 a week. You shouldn't even need to use the calculator on your phone, most stores post price per ounce (or pound) on price labels.
- Don't forget to print coupons before you head to the store.