Understanding the topic
Packaged-food labels can help you compare products, but serving sizes differ between brands. Per-100 g or per-100 mL figures are often more useful for a fair comparison. Ingredients are commonly listed in descending order by weight.
Quick reference
Use these reference points alongside the worked examples below.
| Term | Meaning / value | Why it matters |
|---|---|---|
| Serving size | Manufacturer’s nominated portion | May differ from your actual portion |
| Per 100 g | Standard comparison basis | Compare similar foods |
| Energy | Usually kJ, sometimes kcal | Indicates energy content |
| Sodium | Usually mg | Useful for comparing salt-related content |
| Ingredients | Listed by weight order | Shows major components |
Step-by-step method
- Check the total package size and serving size.
- Use per-100 g values when comparing similar products.
- Read ingredients and allergen declarations carefully.
- Check storage instructions and use-by or best-before dates.
- Consider the overall food and your needs, not just a single number.
Worked examples
Example 1: Comparing cereals
Cereal A has 12 g sugar per 100 g; B has 20 g. A is lower in sugar on that basis.
Example 2: Actual portion
If a 40 g serving contains 8 g sugar, eating 80 g provides about 16 g sugar.
Example 3: Package servings
A 600 g pack with 150 g servings contains four servings.
Common mistakes and useful cautions
- Per-serving numbers can mislead if serving sizes differ.
- Best-before and use-by dates have different meanings; follow food-safety instructions.
- Allergen advice must not be inferred from a simplified nutrition table.
Practice questions
Try each question before revealing the answer.
Question 1: Why compare per 100 g?
Answer: It standardises the amount for a fair comparison.
Question 2: A 200 g pack has 50 g servings. How many servings?
Answer: Four.
Question 3: If 100 g contains 10 g sugar, how much in 30 g?
Answer: 3 g.
What to remember
- Check the total package size and serving size.
- Consider the overall food and your needs, not just a single number.
- Per-serving numbers can mislead if serving sizes differ.