A pack’s price doesn’t tell you whether it is cheap. To compare, bring every product to the same unit: kilo or pound, litre or fluid ounce, or item.
The formula
Price per unit of measure = price ÷ quantity in that unit
(16 oz = 1 lb; 250 g = 0.25 kg)
(16 oz = 1 lb; 250 g = 0.25 kg)
Example: an 8 oz pack at $2.49 costs 2.49 ÷ 0.5 = $4.98 per lb. A 24 oz pack at $5.99 costs 5.99 ÷ 1.5 = $3.99 per lb. A 16 oz store brand at $3.49 costs $3.49 per lb: the cheapest, even though the big pack looked like the deal.
Useful conversions
| Unit | Equals |
|---|---|
| 1 pound (lb) | 0.45359237 kg |
| 1 ounce (oz) | 28.35 g |
| 1 US fluid ounce | 29.57 ml |
| 1 US gallon | 3.785 L |
Common traps
- Multi-buy offers: use the total price and total quantity you take home.
- Drained weight: for canned goods compare the product without the liquid.
- Concentrates: for detergents compare per wash, not per litre.
- Shelf life: the big pack only saves money if you use it before it goes off.
Many shops show a unit price on the shelf label (in the EU it is required, with exceptions, by Directive 98/6/EC). Checking with the calculator is still useful across shops or different formats.
Sources and references
- Directive 98/6/EC on price indication
- International yard and pound agreement (1959): 1 lb = 0.45359237 kg