SAVING money when shopping for groceries might seem as easy as buying loose items instead of prepacked goods, or bulk products rather than small packages.
However, supermarkets are not that simple, especially when weekly specials conspire to confuse shoppers, so there's just one way to make sure you buy the best-value stuff: unit pricing.
The big supermarkets have to display unit prices - the costs of item per unit of measure such as 100g or litre - and consumer specialists say it's not difficult to compare. If you get confused by different measures, there's always the calculator on your smartphone.
Research by the Queensland Consumers Association found that people could save a quarter of their shopping bill simply by switching from a high unit price to low unit price product.
The association's spokesman, Ian Jarratt, said many people followed shopping rules of thumb where buying in bulk was cheaper, loose items were cheaper, and specials delivered the best value.
"It 'ain't always like that," he said.
"You quite often get the situation where the company puts on special the medium-sized package.
"And one of the mysteries of life is why in Coles and Woolworths the packaged carrots are always cheaper than the loose carrots per kilo." Nuts are often similarly priced.
Mr Jarratt said specials could mess with your mind, but comparing unit prices always painted a clear picture.
Trolley Saver founder Sam Lee said some shoppers didn't bother to check unit prices if they saw a big enough discount percentage advertised on an item.
"I've seen shoppers that will buy a smaller sized item at 30 per cent off when the regular priced larger item is actually cheaper per unit," he said.
Shoppers should check the expiry date when bulk buying, Mr Lee said.
"Don't just buy larger packages because the unit price is cheaper - it may end up more expensive after wastage," he said.
"Watch for increased consumption - having larger packaging may cause families to consume more than they normally would.
"Look at unit pricing. Sometimes smaller items on special can be cheaper than larger bulk items - but often it is better to wait until the larger bulk items come on special."
People could set alerts for specials on the free Trolley Saver app, Mr Lee said.