Supermarket chains have been urged to simplify their product labels in order to make comparing products easier.
An investigation by consumer campaign group Which? has found that many shoppers are having to do complex equations in order to find the cheapest deal.
Supermarkets were found to be displaying the prices of similar products using different units, making it difficult for shoppers to understand which product is cheaper.
For example, one supermarket was found to be displaying pre-packaged red onions at 45p an item directly next to loose onions advertised at 95p per kilogram. Another was selling a seven-pack of mini bananas for 99p right next to loose bananas priced at 68p per kilogram.
Richard Lloyd, who is executive director at Which?, stated that price labels should make it easier for customers to find the best deal.
Speaking to The Guardian, he said: "Unit Prices should be a useful tool for people to compare food prices and choose the best value product, which is crucial when we're all looking to save money - but we've found unclear and inconsistent use of unit prices across all the major supermarkets."
The Mail Online report that Which? plan to name and shame the supermarkets guilty of this practice unless they improve their labelling system in the near future.