A cheaper package can cost more for the amount you actually receive. The useful comparison is the full price per matching unit, with any discount, tax and delivery cost you will really pay.
The calculation
First choose a common unit: item, ounce, pound, gram, milliliter or liter. Convert both packages to that unit. For each option, calculate effective checkout cost ÷ comparable quantity. The lower result is the lower cost per unit. FairSpend’s price comparison calculator can do this while you shop.
A worked example
Option A costs $12.99 for 24 identical items: $12.99 ÷ 24 = $0.54125 each. Option B costs $17.48 for 35: $17.48 ÷ 35 = about $0.49943 each. Option B asks for $4.49 more up front, yet each item costs about 4.2 cents less. Measured against A’s unit price, B is about 7.7% cheaper per item. Those figures are an illustration, not a retailer price quote.
If only B needs $5 shipping, its effective total becomes $22.48 and its cost rises to about $0.6423 each. A is then cheaper per item. A percentage coupon or tax treatment can also reverse a result, so enter the final terms that apply to each option separately.
When unit price is not the whole answer
- Compare the same product or a genuinely interchangeable alternative. Ingredients, quality, durability and included accessories can differ.
- Check usable quantity. A product likely to expire before you finish it may be worse value even with a lower unit price.
- Don’t compare a count with a liquid volume unless you know the amount per item. FairSpend rejects incompatible measurement families.
- Rounding the display to cents can hide a narrow difference. Use the underlying totals and quantities when two offers are close.
The FTC also suggests using unit prices to compare products whose package sizes have changed: FTC Consumer Advice on shrinking packaging. For unit conversion references, see NIST measurement equivalencies.
Check before buying: the seller’s final checkout, return policy, product details and any applicable tax rule control the real transaction. See our calculation methods for assumptions and rounding.