"Shrinkflation" gets the headlines, but the underlying issue is broader: package sizes change constantly, for reasons that range from ingredient cost pressure to packaging redesigns to regional formulation differences. If you compare prices without checking size, you're comparing two different products that happen to look similar on a shelf photo.
The three questions to ask before any comparison
- Is the measurement unit the same (weight, volume, or count)?
- Is the size the current size, or are you remembering an old one?
- Does the count include the same contents (e.g., "12 rolls" of paper towels can mean 12 different sheet counts)?
A cereal box that was 525 g last year and is 450 g this year at the same price has had a real, if quiet, price increase of about 17%. Nominal price on the shelf tells you nothing about this; only the unit price does, and only if the unit price is recalculated on the current size rather than remembered from a prior trip.
Worked example: two "family size" bags
Example only: Bag A is labelled "Family Size," weighs 425 g, and costs $5.49. Bag B is also labelled "Family Size," weighs 375 g, and costs $5.29. Nominal price makes Bag B look cheaper by 20 cents. Unit price tells a different story: Bag A is $5.49 ÷ 425 = $1.29/100 g; Bag B is $5.29 ÷ 375 = $1.41/100 g. Bag A is actually about 9% cheaper per 100 g despite costing more at the register.
Marketing size labels vs. actual unit price (example)
| Product | Label | Actual size | Price | Price/100 g |
|---|---|---|---|---|
| Bag A | Family Size | 425 g | $5.49 | $1.29 |
| Bag B | Family Size | 375 g | $5.29 | $1.41 |
Decision rule
Decision rule: ignore marketing size names entirely ("family," "value," "jumbo" have no fixed definition) and compare only the printed weight or volume against the price.
Track size over time, not just price
If you buy the same product regularly, the most useful habit is noting the package size on the receipt or a note app every few months. A price that looks flat for a year while the size drifts down 10% is a real cost increase your monthly grocery total won't obviously reveal, because you're buying the same number of boxes at the same price — you're just getting less in each one.
Cross-brand comparisons need one more check
Even after normalizing units, confirm you're comparing equivalent product tiers — concentrated versus standard detergent, whole versus ground coffee, or pre-cooked versus raw items all carry hidden multipliers on "uses per unit" that a flat per-gram price won't capture. A 2x-concentrated laundry detergent priced at $0.03/wash-equivalent mL beats a standard detergent at $0.02/mL once you account for using half as much per load.
- Recalculate unit price on current package sizes every time — don't rely on memory.
- Discard marketing size labels; use the printed weight/volume only.
- Check for concentration or yield differences (loads per bottle, cups of coffee per bag) before declaring a per-unit winner final.
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.