Aldi, The Co-operative and Waitrose are the latest retailers to commit to improving food labels after Morrisons signed up to a campaign by the Which? consumer group last year.
Which? first called on supermarkets to end hard-to-read and inconsistent labelling last year, arguing that it confuses consumers and makes it difficult for them to identify the best deals.
A survey by the watchdog found 78% of consumers shop around for the best price for their groceries and 43% now compare prices when in stores.
Under the commitment, supermarkets display a consistent unit price, include the unit price of food items on promotion in store and ensure that the labels are clearly visible and adhere to Royal National Institute of Blind People guidelines where possible.
Which? executive director Richard Lloyd said: "Hard-pressed shoppers want to know at a glance what the cheapest deal is without having to get their calculators out, so it's a win for consumers that four major supermarkets have committed to improving their labels.
"In the longer term we want the Government to simplify pricing legislation so that retailers and manufacturers can make food prices even easier to compare."
Business Secretary Vince Cable said: "I welcome the positive steps taken by supermarkets to help consumers get the best value and a fairer deal. Clearer prices and promotions will be a big help for consumers who want to be more savvy and work out how to save more on their weekly shop. In addition, more transparency will boost competition and help support a stronger economy.
"Consumer Minister Jo Swinson has been working closely with the supermarkets and with Which? to explore what more can be done to make prices simpler. This is an encouraging first step and I look forward to other supermarkets following suit."