The site, www.mysupermarket.co.uk, which goes live on Wednesday, is claimed to be the first independent website to allow customers to compare the price of their whole weekly shop at Tesco, Asda, Sainsbury's and Ocado.
Customers shop on the site in the same way as at any grocery website.
The site presents the cost of the basket at the initial retailer selected and then presents the cost at the other three as well.
It also suggests further ways to save money using like-for-like alternatives, such as own label products in place of brands, before transferring the order to the site of the chosen retailer for payment.
The site is searchable through a number of categories, and also by brand and variant, with large visuals for each product. Nutritional information may be added in the future.
The site will initially be free to use but there are plans to charge "minimal" user fees when it is fully established, and also the possibility of introducing product promotions to generate advertising revenue.
The site, which cost a seven-figure sum to establish, is owned by a group of private UK investors described as "online experts". Johnny Stern, director of mysupermarket.co.uk, claimed that the site could save shoppers about 20% on their weekly shop.
"We think mysupermarket.co.uk will have the same impact on the online grocery market that eBay had with online shopping," said Stern. "Many shoppers have told us that they feel they could be spending their money much more wisely when it comes to groceries but they just don't know how to do it.
"The site makes it easier for customers to track down deals so that they feel more in control than ever before."
Stern said that the site was yet to be endorsed by any of the four retailers, but that the company would be willing to work with any supermarket or retailer.