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Unit Price Math for Holiday Sales: Is the Big Pack Really Cheaper?

By Smart Budget Sheets November 10, 2026
Unit price math: is the big pack really cheaper? Three worked examples.

Sale tags compare against a ‘was’ price. The number that actually matters is the price per unit: per ounce, per sheet, per load, per 100 grams.

The formula

Unit price = price / quantity.

Example 1: detergent

  • 64 loads for $11.99 = about 18.7 cents a load.
  • 110 loads ‘on sale’ for $21.49 = about 19.5 cents a load.

The big ‘deal’ costs more per load than the regular size.

Example 2: multi-buy offers

‘3 for $10’ on a $3.79 item saves about $1.37, but only if you would really use all three before they expire. Food that gets thrown away has an infinite unit price.

Example 3: percent off vs bigger pack

  • 20% off a 12-pack at $8.99 = $7.19, about 60 cents each.
  • 24-pack at $13.49 = about 56 cents each.

Here the bigger pack still wins, even against the discount.

Rules of thumb

  1. Compare in the same unit. Shelf labels sometimes switch between per ounce and per count on the same aisle.
  2. Bigger is usually cheaper per unit, but not always, especially when the small size is the one on promotion.
  3. Only buy bulk you can store and use before it goes off.
  4. Set a total budget for the shopping trip first; unit price helps you choose between options, not decide whether to buy at all.

Free tools

General information, not financial advice. Figures are rounded examples.

#personalfinance #budgeting #frugal
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