Is it really half price? How to read a unit price

Every shelf label in a large Australian supermarket carries two prices. The big one is what you pay. The small one, usually in grey somewhere near the corner, is the unit price — the cost per 100g, per 100mL, per kilogram, per litre, or per item.

That second number is the only figure on the label that lets you compare one product with another honestly, and it is the single most useful habit you can build in a supermarket. It is also the number that tells you whether a half price special is genuinely good value or just a smaller pack at a discount.

Why unit pricing exists

Unit pricing became mandatory for large grocery retailers in Australia in 2009 and is now governed by the Competition and Consumer (Industry Codes — Unit Pricing) Regulations, enforced by the ACCC. Supermarkets above a certain size must display a unit price on shelf labels, in catalogues and online, in a prescribed and legible form.

The reason it was made compulsory is straightforward: pack sizes in Australian supermarkets are not standardised. Two brands of the same product will be sold in 375g and 400g packs, or 900mL and 1L bottles, and comparing them in your head at the shelf is genuinely difficult. Unit pricing removes the arithmetic.

The four things unit pricing catches

1. The smaller pack at half price that is still worse value

This is the most common one. A 30-tablet pack of dishwasher tablets at half price can easily work out dearer per wash than the 60-tablet pack at its ordinary price, because the large pack carries a permanently lower unit rate. The half price sticker is accurate — it really is 50% off that pack's regular price — and you still end up paying more per tablet.

2. Concentrated versus regular

Laundry liquids, cordials, cleaning concentrates and coffee are all sold in concentrated and standard forms at the same nominal volume. Unit pricing by volume does not adjust for concentration, so here you have to read the number of washes, number of serves or number of cups on the front of the pack. Two 1L bottles at the same unit price can be rated for 20 washes and 40 washes.

3. Fresh produce sold by pack versus by weight

A pre-packed bag of apples is unit-priced per kilogram, and so is the loose bin next to it. They are frequently very different numbers, and the loose fruit is usually cheaper — you are paying for the bag, the sorting and the convenience. The same applies to pre-cut vegetables, where the premium can be several hundred per cent.

4. The "value" pack that is not

Large packs are usually cheaper per unit, but not always. Family-size and bulk formats are sometimes priced at a premium precisely because shoppers assume bigger means cheaper. Unit pricing catches this in two seconds.

How to do it quickly

You do not need to check the unit price on everything. Use it in three situations:

• When two pack sizes of the same product sit next to each other.
• When you are deciding between brands and one of them is on special.
• When something is marketed as a value, bulk or family pack.

For everything else — the item you buy every week in the size you always buy — you have already made the comparison, and repeating it adds nothing.

What half price actually guarantees

A half price special guarantees exactly one thing: that this product is currently around 50% cheaper than the price it normally sells for at that supermarket. That is genuinely useful information — it means you are buying at the bottom of that product's own price range, and it is the right moment to buy if it is a product you use.

What it does not guarantee:

• that it is the cheapest option in its category (a rival brand may be cheaper at full price);
• that it is the cheapest per unit (a bigger pack may be better value);
• that it is cheaper than the other supermarket, or than Aldi, or than a discount pharmacy;
• that the "was" price is what you would ever actually have paid, if the product is nearly always on some form of promotion.

None of that makes half price specials a con. It makes them one input into a decision rather than the whole decision.

A worked example

Say you are buying laundry liquid and you have three options in front of you:

Option	Shelf price	Size	Unit price
Brand A, half price	$9.00	1L	$0.90 / 100mL
Brand B, full price	$16.00	2L	$0.80 / 100mL
Supermarket brand	$7.00	1L	$0.70 / 100mL

The half price item is the one with the sticker on it and the worst value of the three. If Brand A is the one you like and the others do not work for you, it is still the right buy — you are getting your preferred product at the bottom of its range. But if you were only choosing on price, the sticker pointed you at the wrong shelf.

Now change one number: make Brand A a 2L bottle at $9.00 half price, and it becomes $0.45 per 100mL — comfortably the best value on the shelf, and worth buying two of. Same sticker, completely different decision. That is the whole argument for reading the small grey number.

Next: what is actually worth stockpiling at half price, and the traps that turn a saving into a loss.