Which product is cheaper? Compare prices per unit and save on groceries.
Price Comparison Guide
Why compare unit prices?
Comparing unit prices is the most effective way to save money in the store. The same brand in different packaging can have significantly different price per 100g or 100ml. Larger packages often offer better value, but not always - check unit price to avoid apparent deals. Many stores put unit price on the label, but you can also quickly calculate it yourself.
What to watch when shopping?
- Compare the same products - compare unit prices only for comparable products
- Check expiration date - cheaper product with short date may not be worth it
- Pay attention to promotions - "3 for 2" doesn't always mean savings
- Buy in season - fruits and vegetables are cheaper in season
Smart shopping strategies
Plan shopping with a list and stick to it to avoid impulse purchases. Compare prices in different stores - sometimes the same products vary significantly in price. Use coupons and promotional apps. Buy products in larger quantities when on sale and freeze or store them. Also remember store brand products - they often offer the same quality for lower prices than brand equivalents.
The biggest pack is often the most expensive per unit
Buying in bulk is treated as an obvious saving, and often it is the opposite. Pack sizes are priced against what shoppers expect rather than against a consistent rate, so the largest box on the shelf can quietly cost more per hundred grams than the medium one beside it.
How it works
- Reduces every option to the same unit — per 100 g, per litre, per item — so the prices are actually comparable.
- Handles multi-buy offers, which change the effective unit price without changing the shelf price.
- Removes the guesswork from pack sizes chosen specifically to be hard to compare.
unit price = price ÷ quantity × unit for a multi-buy: effective unit price = (units paid for × price) ÷ (units received × quantity) × unit always compare at the same unit, never at the shelf price
Worked example
Three sizes of the same product, and a promotion on the smallest.
- 500 g at 3.49 → 0.698 per 100 g
- 750 g at 4.99 → 0.665 per 100 g
- 1 kg at 7.29 → 0.729 per 100 g
- 3-for-2 on the 500 g: 6.98 for 1,500 g → 0.465 per 100 g
The 1 kg pack is the worst value — 9.6% more per unit than the 750 g. And the promotion on the smallest pack beats the best regular price by 43%, which no amount of buying big would have matched.
Reading the result
- Unit pricing on shelf labels is the fastest check available, where it is displayed. Where it is not, or where the units differ between neighbouring products, that inconsistency is doing work — comparing per 100 g against per item is not a comparison at all.
- Bulk only saves if you use it. A larger pack at a genuinely lower unit price is a loss if a third of it is thrown away, which makes perishables a different calculation from tinned or dry goods.
- Multi-buys are where the real movement is. A 3-for-2 is a 33% discount on the unit price and will usually beat any size difference, but only if you would have bought all three anyway.
- Watch for pack sizes that shrink while the price holds. Comparing today's unit price against your memory of the old shelf price will miss it; comparing per unit against the alternatives on the shelf will not.
Common questions
- Isn't buying in bulk always cheaper?
- No. In this example the 1 kg pack costs 9.6% more per 100 g than the 750 g. Larger packs are priced on the expectation that they are better value, which is precisely what allows them not to be.
- How do I compare a multi-buy against a bigger pack?
- Convert both to the same unit. A 3-for-2 means you pay for two and receive three, so divide the price of two by the quantity of three. Here that gave 0.465 per 100 g against 0.665 for the best regular price.