What is The Grocer 33 and how does it work?

Over the course of the years the Grocer 33 has evolved considerably to reflect retail market dynamics and, through partnering with new service providers, to offer greater analytics and online functionality. But the three core elements remain the same:

1. A weekly price comparison survey of a basket of 33 items which examines which retailer is the cheapest each week. This also includes information on promotions and inflation.
2. A nationwide mystery shopping survey, which compares and scores the in store and online experience.
3. An availability study which tracks out of stock and not stocked items from our weekly basket.

This unique combination of a weekly and constantly changing price comparison survey with a nationwide mystery shopping survey provides store managers, supermarket head offices, and suppliers with invaluable insights into retail execution as well as pricing and promotional trends across Asda, Morrisons, Sainsbury’s, Tesco, and Waitrose. We also feature regular guest retailer appearances from Aldi, Amazon, Iceland, Lidl, Ocado and, from July 2025, Marks & Spencer Foodhalls, to deliver additional capability and comparative tests.

The data we collect not only calculates the grocer offering the cheapest prices and the best service and availability each week; it is also part of an annual competition. At the end of the 49-week period in which the surveys are conducted we award three Grocer Gold Awards based on totting up the respective scores over the course of the year, while the winners of the store of the week are also put forward for the annual Store Manager of the Year competition.

How do you choose the products?

Every week we shop 33 identical or carefully matched and ratio-adjusted items including branded and own-label products, value lines and premium ranges, weighted to reflect consumption across the major grocery categories. The basket of 33 goods is refreshed weekly to ensure we’re checking a wide range of products over the course of the year.

How do you collect the prices?

Price collection is conducted online every Monday using Assosia’s Price and Promotion platform, which provides real-time analytics and powerful insights across all categories within the grocery sector. Some price collection also takes place in-store for verification purposes using their retail audit teams. You can contact Assosia or email services@assosia.com

How do you measure prices and determine the cheapest retailer?

Using pricing and promotion data collected by Assosia, we calculate the total cost of each retailer’s baskets using six different pricing methodologies: the base price; the display price; the multibuy price; the loyalty display price; the loyalty multibuy price; and the all-inclusive price. Since 2024 the winner each week has been determined using the loyalty display price – in other words what a shopper with a retailer’s loyalty card or app would have paid for the single item on our shopping list

Why did you change the way you measure prices?

Over the years we’ve enhanced the Grocer 33 in numerous ways to ensure it remains relevant and reflective of the latest market dynamics. The change to the methodology we use to rank the cheapest supermarket every week was informed by consumer research conducted by Toluna & Harris Interactive through which we now include loyalty prices in our price measurement. You can read a fuller explanation of the reasons for the changes in the explanation here.

Why should suppliers read it?

The Grocer 33 price comparison isn’t just about retailer competition. It also tracks prices and price inflation (week on week, month on month and year on year) at an individual sku level to provide a more complete picture of supermarket product pricing and promotional strategies. You can check the latest winners here.

Why don’t you shop the discounters more regularly?

The Grocer 33 list is refreshed weekly to ensure we’re checking a wide range of products over the course of the year. Due to the limited assortments of the discounters it is impossible to find a sufficient number of product matches without returning to the same items every week. You can find the latest Super 33s here.

Do you track discounter prices in any other way?

Yes. The KVI Price Tracker measures weekly retail price changes on key value items at Aldi and Lidl as well as Asda, Morrisons, Sainsbury’s, Tesco and Waitrose. We are able to do this as the 200-strong list of items does not change and does not require a product match across all seven retailers. You can check the latest reports here.

How do you measure customer service in the Grocer 33?

Every week a nationwide team of mystery shoppers visit supermarkets across the UK armed with the list of 33 items. Shopping surveys take place on either a Friday, Saturday or Sunday, within a two-hour time window on the predetermined day each week to ensure there is a level playing field between the shops. The mystery shoppers assess the car park or public transport access, in-store experience, store standards, shop floor service and checkout experience, as well as checking the availability of the 33 items, noting which are out of stock and which are not stocked. The Gold award goes to the supermarket with the best service and availability over the 49-week period. You can check the latest winners here.

How has the methodology changed?

Over the years we’ve updated the Grocer 33 customer service methodology to ensure it remains relevant and reflective of the latest market trends. The latest changes introduced in July 2025 include measures to assess supermarkets on their management of self checkout machines to reflect their near-universal usage, but at the same time we’ve ensured surveys will continue to measure till-based checkout operators too.

How do you measure availability?

In the course of the mystery shopper visits to the stores a separate tally is kept of supermarket availability. Each shopper checks the same list of 33 items, noting which are out of stock and which are not stocked. The Gold award goes to the supermarket with the best availability across the 49-week period, based on overall availability percentages but the annual competition is only awarded to supermarkets that feature regularly

Who are your mystery shoppers?

Our mystery shops are conducted by Assosia’s field team of over 3,000 expert mystery shoppers. They are trained to provide independent assessments of customer service and availability, and complete a detailed report designed by The Grocer’s editorial team.

How do you choose where to shop?

Each week we shop in a different location. But from July 2025, all five mystery shops will be conducted in the same location that week. This will give our readers a side-by-side comparison of supermarkets in directly competing locations. On occasion, some towns or cities will not have our five regularly shopped retailers. When this happens, we will swap in an alternative retailer in that area. But we expect this to happen very rarely.

However, some weeks, we will conduct special themed shops instead of visiting the same location, to provide further topicality and achieve greater geographic reach.

Do you ever conduct online mystery shops?

Yes. Separate tests are conducted in a quarterly ‘Online Grocer 33’. This uses the same shopping list but features a different methodology, to assess areas such as website navigation and delivery. From July 2025, when online Grocer 33 shops feature, they will replace store-based shops and the results will contribute to the overall awards for service and availability.

^{This article was updated on 4 July 2025 to reflect further changes to the Grocer 33 introduced from 5 July.}