Bigger isn’t always cheaper
Stores sell the same item in different sizes and brands. Comparison shopping means checking which option gives the best value. The key tool is the unit price.
Finding unit price
Unit price = total price ÷ quantity
| Product | Price | Quantity | Unit price |
|---|---|---|---|
| Cereal A | $4.49 | 400 g | $1.12 per 100 g |
| Cereal B | $6.29 | 750 g | $0.84 per 100 g |
Cereal B is the better buy.
Tip: Compare using the same unit (per 100 g, per kg or per item). Many stores print the unit price on the shelf label, but check that both labels use the same unit.
Comparing without a calculator
Scale to a common quantity.
Example: 3 L of juice for $5.40 or 2 L for $3.80?
- Price for 6 L: 2 × $5.40 = $10.80 vs 3 × $3.80 = $11.40
- The 3 L jug is cheaper.
Deals and offers
| Offer | Think |
|---|---|
| "2 for $5" | $2.50 each; you usually don’t need to buy 2 |
| "Buy 2, get 1 free" | 3 items for the price of 2: one-third off each |
| "30% more free" | 1.3 times the quantity for the same price |
| "Save $1.50" | compare the new unit price |
Example: "Buy 2 get 1 free" on $3 items = $6 for 3 = $2 each.
Other things to consider
The lowest unit price isn’t always the smartest choice:
- Waste: Will you use it all before it spoils?
- Storage: Do you have room for bulk packs?
- Budget: Can you afford the larger upfront cost?
- Quality and preference: Is the cheaper brand as good?
- Travel costs: Driving across town to save 50 cents may cost more in gas.
Worked examples
Example 1: 12 eggs for $4.68 or 30 eggs for $10.80?
$0.39 vs $0.36 per egg → 30 eggs.
Example 2: Shampoo: 400 mL for $5.20, or 1 L for $11.50?
$1.30 vs $1.15 per 100 mL → 1 L.
Example 3: A $4.00 bottle of 500 mL offers "25% more free". New unit price?
625 mL for $4.00 → $0.64 per 100 mL (was $0.80).
Common mistakes
- Comparing total prices instead of unit prices.
- Mixing units (per 100 g vs per kg).
- Ignoring waste or need.
Try it yourself
- 6 muffins for $5.10 or 4 for $3.60. Better buy?
- 2 kg of rice for $4.80 or 5 kg for $11.25?
- "3 for $10" vs $3.49 each. Which is cheaper per item?
- Why might a family of two not buy the bulk 5 L milk?
Answers: 1) 6 muffins ($0.85 vs $0.90) 2) 5 kg ($2.25 vs $2.40 per kg) 3) 3 for $10 ($3.33) 4) It might spoil before they finish it.
Quick recap
- Unit price = price ÷ quantity.
- Compare in the same units to find the better buy.
- Consider waste, storage and need, not just price.