Comparing Unit Prices

Understanding the concept

Unit pricing shows what a product costs for a standard quantity. It is useful when packs have different sizes, but quality, waste and suitability still matter.

This lesson uses simple, fixed examples to explain the method. Identify the quantities, choose the correct formula, and check that the units in your answer make sense.

Unit price formula

Unit price = total price ÷ quantity. For price per kilogram, express the quantity in kilograms first.

Write down the original values before substituting numbers. Keep full precision during the calculation and round only when presenting the final result.

Worked example

Question: Which is cheaper per kilogram: 750 g for $6 or 1 kg for $7.50?

1. Convert 750 g to 0.75 kg.
2. First item: $6 ÷ 0.75 = $8 per kg.
3. Second item: $7.50 ÷ 1 = $7.50 per kg.

Check the answer against the original question. An answer should include the appropriate unit or percentage where relevant.

Key points to remember

• Compare the same units and similar products.
• Bulk buying only saves money if you use what you buy.
• Check promotional prices and whether pack sizes have changed.

Common mistakes

Comparing shelf prices without accounting for the different pack sizes.

To avoid this, label each number, identify the starting amount and use a quick estimate to see whether the final answer is reasonable.

Try it yourself

A 2 L bottle costs $5. What is its price per litre?

Comparing unit-price labels

Use this table as a quick reference. Check which quantities and units each method requires before calculating.

More worked examples

Work through each calculation and notice how the method changes with the question.

Example 1: Compare rice: 1 kg for $4.80 or 2 kg for $8.40

Method: 4.80 ÷ 1 = 4.80/kg; 8.40 ÷ 2 = 4.20/kg.

Example 2: Compare juice: 750 mL for $3 or 1 L for $3.60

Method: 3 ÷ 0.75 = 4/L; 3.60 ÷ 1 = 3.60/L.

Example 3: Compare tissues: 100 for $2.20 or 180 for $3.60

Method: 2.20 ÷ 100 = 2.2¢; 3.60 ÷ 180 = 2¢.

Using this in everyday life

Unit pricing helps compare different package sizes, but a larger pack is not automatically better. Consider waste, storage, quality and whether you will use the quantity.

Before you begin: Identify what the question asks, write down the given information, use matching units, then estimate the result to catch mistakes.

Extra practice questions

Try these independently before expanding the answer. Show your working, not just the final number.