How do you work out which pack is cheaper?
· Avinash Kumar
Voice Calculator runs on iPhone. The app is available in English, Japanese, German, French, Spanish, Portuguese and Chinese.
Divide the price by the amount. The pack with the lower price per unit is cheaper. To compare a 750 g box at $4.20 with a 500 g box at $3.10: 4.20 ÷ 7.5 = $0.56 per 100 g, and 3.10 ÷ 5 = $0.62 per 100 g. The bigger box wins.
Pick one unit and stick to it
Most mistakes come from comparing different units.
| Item | Price | Amount | Per 100 g / per unit |
|---|---|---|---|
| Cereal A | $4.20 | 750 g | $0.56 / 100 g |
| Cereal B | $3.10 | 500 g | $0.62 / 100 g |
| Batteries 8-pack | $9.99 | 8 | $1.25 each |
| Batteries 20-pack | $21.99 | 20 | $1.10 each |
Dividing by “hundreds of grams” (7.5 instead of 750) gives numbers you can read at a glance.
Shelf label traps
- One label in price per ounce, the next in price per count.
- Multi-buy offers (“2 for $6”) that the label ignores.
- Pack sizes that shrank while the price stayed the same.
Doing it in the aisle
With a basket in one hand, typing is awkward. In Voice Calculator (my app) you can say “4.20 divided by 7.5 equals” and hear the result, then do the second pack. Both lines stay on the tape, so you can compare them on screen. It also keeps a running total in the Dynamic Island and on the Lock Screen if you’re adding up the basket as you go.
Related: adding up receipts, scaling a recipe by voice and the Voice Calculator guides.
Questions people ask
- What is the formula for price per unit?
- Price divided by quantity. A 750 g box at $4.20 costs 4.20 ÷ 750 = $0.0056 per gram, or $0.56 per 100 g.
- Why do shelf labels sometimes disagree?
- Labels can use different units for similar items, for example price per ounce on one and price per count on another. Convert both to the same unit before comparing.
- Is the cheapest unit price always the best buy?
- Only if you'll use it all. A bigger pack that goes off before you finish it costs more per unit you eat.
Voice Calculator
A calculator you talk to: say the numbers, check each one on the tape, hear the total.
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