Packaging, handling, and shelf-space costs are largely fixed per unit sold, regardless of how much product is inside. A retailer pays roughly the same amount to stock, scan, and shelve a small bottle as a large one, which means those fixed costs are spread over less product in a small package — pushing its per-unit price up relative to a larger size of the same product, even before any bulk discount is applied.
Worked example
Example only: a travel-size bottle of shampoo, 90 mL, sells for $3.99 ($4.43/100 mL). The standard 355 mL bottle of the identical formula sells for $6.99 ($1.97/100 mL). The travel size costs more than double per 100 mL, not because the formula is different, but because the fixed packaging and handling cost is a much larger share of a $3.99 sale than a $6.99 one.
Same shampoo, three sizes (example)
| Size | Price | Price/100 mL | vs. largest size |
|---|---|---|---|
| 90 mL (travel) | $3.99 | $4.43 | +125% |
| 355 mL (standard) | $6.99 | $1.97 | baseline |
| 700 mL (value) | $11.49 | $1.64 | -17% |
Decision rule
Decision rule: the smallest package size is a convenience premium, not a value option, in nearly every category. Only choose it when you have a genuine need for portability or a trial quantity — not to save money upfront.
When the pattern reverses
It's not universal. Perishables with a real risk of waste (see the bulk-buying guide) can flip this pattern: a large size that goes bad before use has a higher effective cost than a small size fully consumed. The fixed-cost-per-package effect is strongest for shelf-stable, non-perishable goods — health and beauty items, cleaning supplies, pantry staples — and weakest or reversed for fresh food with a short usable window.
"New and improved" smaller packaging
Watch for cases where a manufacturer reduces a mid-size package (say, from 500 g to 450 g) at the same price, effectively converting what used to be the best per-unit value into a worse one than the large size, without changing either package's shelf price. This is common enough that re-checking unit price on your regular purchases every few months — not just when you first pick a size — is worth the ten seconds it takes.
Store brand and generic sizing
Store brands often skip the smallest, most fixed-cost-punished size entirely and start at what would be the "standard" size for the category, which is part of why store brands frequently show a better unit price even before considering their generally lower base pricing. If the smallest available size of a name brand is the only option that fits your storage or usage constraints, checking whether a store brand offers a better-sized alternative is worth the comparison.
- Assume the smallest package size carries the worst per-unit price unless proven otherwise.
- Recheck unit price periodically — mid-size packages can quietly shrink below their historical value position.
- Reserve small sizes for genuine trial or portability needs, not routine budget shopping.
- Check store-brand sizing options if the smallest name-brand size is your only fit.
All figures in this guide are illustrative examples, not current prices. Cotco does not sell products and is not affiliated with any retailer. Verify prices, sizes, and product details with the seller before buying.