Look at this image as an example
The image shows two different price tags.
In the first one, the retail price is $1.62 for one 32 oz. yogurt. The unit price, in the red box, is $0.05 per oz.
In the second one, the retail price is $0.72 for one 6 oz. yogurt, but the unit price is $0.12 per oz.
Based on the unit price, you can determine that the larger, 32 oz. yogurt is the better buy because you are getting more for your money.
TOTAL PRICE ÷ SIZE = UNIT PRICE
$0.72 ÷ 6 oz. = $0.12
The unit price of this yogurt is $0.12 per oz.