Key takeaway: The unit price of an item is its total cost divided by the number of units it contains, such as dollars per ounce, and it lets shoppers compare packages of different sizes fairly.
Grade 66.RP.A.3bRatios, Rates and Percents
Definition of Unit Price
The unit price is what one unit of a product costs: one ounce, one pound, one pack, one item. It is a unit rate where the first quantity is money.
Stores post it on shelf tags because a bigger package is not always cheaper per unit. To compare two sizes, find the unit price of each in the same unit and choose the smaller one. Round only at the end, since cents can hide a real difference.
Formula and notation
Divide the price by the quantity:
\[\text{unit price} = \frac{\text{total price}}{\text{number of units}}\]
The result is written as dollars per unit, for example \(\$0.06\) per fluid ounce. Use the same unit for both products before you compare.
Key facts
- Unit price equals price divided by quantity; multiplying back by the quantity returns the total cost.
- The smaller value per unit is the better buy when the quality is the same.
- Both packages must be measured in the same unit, such as fluid ounces, before comparing.
- A sale price needs a new unit price, because the quantity stays the same but the cost changes.
Unit Price example
Apple juice comes in a 64-fluid-ounce bottle for \$3.84 and in a 96-fluid-ounce bottle for \$5.28. Which bottle has the lower unit price?
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Bottle A: \(\$3.84 : 64 = \$0.06\) per fluid ounce.
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Bottle B: \(\$5.28 : 96 = \$0.055\) per fluid ounce.
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Compare: \(\$0.055 < \$0.06\).
The 96-ounce bottle costs \$0.055 per fluid ounce, so it is the better buy.
Common mistake
Watch out
Jonas sees \$3.84 and \$5.28 and says the 64-ounce bottle is cheaper, so it is the better deal.
Why it is wrong
Comparing totals ignores how much you get. The bottles hold different amounts, so divide each price by its volume first. After dividing, the bigger bottle costs less for every ounce.
Related terms and lessons
Browse the glossary: A–Z list · Grade 6 vocabulary · Ratios, Rates and Percents