Unit Price Shopping: Compare Pack Sizes Without Being Misled
The shelf price answers what you pay today. Unit price answers how much product you receive for each dollar—but only when the units describe the same usable thing.
Choose a meaningful common unit
Grams and ounces work for food by weight; milliliters and fluid ounces work for volume. Items such as paper towels may be clearer per sheet or per square meter, while detergent can be compared per standard load rather than per bottle.
Convert before dividing
Do not compare $0.40 per ounce with $0.012 per gram directly. Convert both quantities first. One ounce is approximately 28.35 grams, so a $0.40-per-ounce item costs about $0.0141 per gram.
Normalize the package before choosing
The cheaper package price can have the higher unit price.
| Scenario | Smaller option | Larger option | Result |
|---|---|---|---|
| Coffee | 340 g / $6 = 1.76¢/g | 900 g / $14 = 1.56¢/g | Larger is 11.8% cheaper per gram |
| Detergent | 40 loads / $12 = 30¢/load | 70 loads / $24 = 34.3¢/load | Smaller is cheaper per load |
| Yogurt with expected waste | 500 g / $3; use all | 1 kg / $5; use 70% | Usable cost ties at about 0.6¢/g |
Adjust for concentration and usable quantity
A concentrate can look expensive per milliliter but cheap per prepared serving. Bone-in meat, products packed in liquid, and rolls with different sheet sizes also require a usable-quantity adjustment.
- Use the manufacturer’s standard dose when realistic.
- Compare drained weight when the packaging provides it.
- Account for sheets, layers, or area—not just roll count.
- Reduce the expected usable amount when spoilage is likely.
Include the cost of buying access
A warehouse pack is not automatically cheaper if the comparison ignores membership fees, travel, delivery, or the cash tied up in inventory. Allocate those costs across the purchases that actually benefit from them.
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