The short answer
How do you compare unit prices?
Divide the price by the quantity. A $4.99 12-ounce bag costs 4.99 ÷ 12 = 41.6¢ per ounce; a $8.49 24-ounce bag costs 35.4¢ per ounce, so the bigger bag is 15% cheaper per ounce. When sizes use different units, convert first: 1 lb = 16 oz = 453.6 g, 1 kg = 2.2 lb, and 1 US gallon = 128 fl oz = 3.785 litres.
Unit conversions
| From | Equals |
|---|---|
| 1 ounce (oz) | 28.35 grams |
| 1 pound (lb) | 16 oz = 453.6 g |
| 1 kilogram (kg) | 1,000 g = 2.205 lb |
| 1 US fluid ounce (fl oz) | 29.57 ml |
| 1 litre (l) | 33.81 fl oz |
| 1 US gallon (gal) | 128 fl oz = 3.785 l |
Weight ounces (oz) and fluid ounces (fl oz) measure different things; compare weight with weight and volume with volume.
When bigger is not cheaper
- Sales on small sizes. A discounted small pack can beat the regular price of the family size.
- Multi-buy offers. "2 for $5" on 10-oz cans is 25¢ per ounce; compare it with the large can's unit price rather than assuming the deal wins.
- Waste. The cheapest unit price only saves money if you use it all before it spoils or expires.
- Shelf labels. Shelf tags show unit prices, but stores sometimes use different units for similar products (per ounce versus per count); convert before comparing.
Worked examples
Coffee
$11.99 for 2 lb (32 oz) is 37.5¢ per ounce, about 6% more than the 24-oz bag at 35.4¢.
Laundry detergent
$13.97 for 92 fl oz is 15.2¢/fl oz; $19.97 for 150 fl oz is 13.3¢/fl oz. The large bottle saves about 12%.
Paper towels
Compare per sheet or per square foot, not per roll; "double rolls" vary between brands.
Frequently asked questions
How do I calculate unit price?
Divide the price by the quantity in the same unit. $8.49 for 24 oz is 8.49 ÷ 24 = $0.354 per ounce.
How do I compare prices in ounces and grams?
Convert to one unit first: 1 ounce = 28.35 grams. The calculator converts automatically.
Is the bigger size always cheaper?
No. Sales on smaller sizes and multi-buy offers can make smaller packs cheaper per unit, so compare the unit price each time.
How many ounces are in a pound?
16 ounces (weight).
Can I compare a weight with a volume?
Not directly. Ounces of weight and fluid ounces of volume measure different things; compare products sold in the same kind of unit.