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Inconsistent Unit Measurement of Products in Supermarkets Impedes Direct Price Comparison Calling for a Unified Unit Price to Help the Public Shop Wisely

  • 2021.03.15

When doing grocery shopping, many may be influenced by “traditional wisdom” and consider bigger or multiple packages more of a bargain than smaller packages or a single item. The Consumer Council gathered the pricing information of 12 categories of pre-packaged food products from 4 large supermarket chains, and revealed the “real” price of each product by calculating the respective unit price based on their net weight or net volume. The result showed the unit price of bigger packages was not necessarily cheaper than smaller packages, whereas the unit price of products in cases might be more expensive than a single item. In addition, although different flavours of the same product/brand were marked with the same price, their unit price could vary up to 80% due to different net weight or volume. The unit price of the same product/brand having identical weight, but different packaging could also vary from over 40% to 60% due to different packaging. Since there is no uniform standard adopted by supermarkets when displaying the net weight or net volume of each product on shelves, and products of the same type may be packed using different dimensions, such as weight, volume, or size, the product with the lowest marked price on the shelves might not be the best value for money. Besides, consumers may find it difficult to compare the prices directly, impeding price comparison.

The Council suggests that large supermarket chains take the lead and make reference to related policies and experiences from overseas countries and regions, like Australia, Canada and the United States, to display the unit price of products with a standard unit measurement (e.g. per 100g or per 100ml). This could help consumers shop wisely through easy price comparison between products of different packaging and brands.

The survey was conducted in December last year. The price information of 12 categories (over 1,000 items) of pre-packaged food from 4 large supermarket chains were collected for 4 times. The categories covered “breakfast cereal”, “evaporated milk/condensed milk”, “fresh milk/milk beverage”, “packaged rice”, “edible oil”, “carbonated soft drinks”, “canned food”, “pasta sauce/ketchup”, “sugar”, “jam/peanut butter”, “tofu” and “fresh produce”. Prices collected were converted to unit price of “per 100g” or “per 100ml” based on its net weight or volume. Products with larger variance in their unit prices were sorted into different groups for further analysis. Examples included 20 groups of products of the same brand in which the unit prices of smaller packages were lower than bigger packages; and 18 groups of products of the same brand in different flavours and same marked price but came in different weights, etc.

The survey found that in the 20 groups of products with varying package sizes, the unit prices of bigger packages were 1.3% to 42.2% more expensive than their smaller packages. The greatest variation was seen in 1 condensed milk. In the 4 supermarkets, the unit price of its 450g squeeze bottle was $6.87 and $7.31, whereas its 185g tube pack had a unit price between $5.14 and $6.76, revealing that the unit price of the bigger package was 1.6% to 42.2% higher than the smaller package. The second example was 1 peanut butter, the unit price of its 510g bigger pack from 3 supermarkets was $7.24 and $7.63, 4% to 19.9% more expensive than the unit price of its medium pack which fell between $6.04 and $7.34.

The survey also found that the unit prices of products in cases were not necessarily lower than a single item. Take the original flavour milk beverage (946ml per pack) as an example, the unit price of its 12-pack full case was $1.79, 10.5% higher than the unit price of its 3-pack, which was $1.62.

For products of the same brand, different flavours although packed alike and marked with the same price, the unit prices of different flavours may vary because of their different net weight or volume. Among the products, 18 groups had a more obvious discrepancy in their unit prices. For example, the unit price of the “original” flavour and “maple & brown sugar” flavour of 1 instant oatmeal sold in 2 supermarkets was $33.9. However, its “original” flavour weighed only 224g while its “maple & brown sugar” flavour weighed 328g. In unit pricing, the “original” flavour was 46.3% more expensive than the “maple & brown sugar” flavour. Another example of 1 pasta sauce from 1 supermarket, the net weight of 4 different flavours ranged from 75.3g (peperoncino) to 135g (tomato cream). Although they were all sold at the price of $29.9, their unit prices ranged from $22.15 to $39.71 with a difference of 79.3%.

The packaging of products may also affect their marked prices. In the 6 groups of related examples, the unit prices of the 1.5kg bag pack, 800g tin pack and 800g bag pack of the same brand of instant and quick cook oatmeal varied: the 800g tin pack ($4.11) sold in 1 of the supermarkets was 22.3% and 43.7% higher than the 800g bag pack ($2.86 and $3.36 recorded in 4 surveys), and 28.8% higher than the 1.5kg bag pack ($3.19). Although in another supermarket, the unit prices of the 800g tin pack and 800g bag pack were the same ($3.36) but they were still 5.3% and 17.5% higher than the 1.5kg bag pack ($2.86 and $3.19 recorded in 4 surveys).

Products offering handy packaging may have different unit prices. Take the unit price of 1 ketchup as an example, its 20oz (567g) plastic squeezable bottle (from $3.79 to $4.04) in 3 supermarkets was 22.7% to 36% higher than the 320g bag pack of the same product ($2.97 to $3.09) and 0.8% to 36% higher than the 300g bottle ($2.97 to $3.83).

Different packaging of the same product might use different units of measurement in displaying its weight or volume. Such occurrence found in both physical store and online shopping platform of supermarkets is confusing to consumers. Take the full cream evaporated milk sold in all 4 supermarkets as an example, its 450ml carton and 156ml 12-capsule pack were indicated as “ml”. However, its 160ml can was indicated as “g” as its net weight (170g). There were also cases where the supermarkets used different units to indicate the weight of the same type of products. For instance, 1 supermarket used “g” for the net weight of a large ketchup (680g/24oz) while 3 supermarkets used “oz” instead; in another case, 2 supermarkets used both “g” and “oz” for the net weights of the same canned fruits of the same brand with different packaging, adding difficulty for consumers to compare product price directly.

As for the 10 groups of pre-packaged fresh produce, the weight units marked by each supermarket varied vastly, from per lb, per kg, per 100g to even per catty, causing confusion to consumers. Take “fresh lean pork” as an example, 3 supermarkets marked the price as $78/lb, $98.5/lb and $154.3/kg. After conversion to the same unit, their unit prices were $17.2, $21.72 and $15.43 respectively. Without doing so, it was impossible to know that $15.43 was the best bargain, and that its unit price was 11.5% and 40.8% cheaper than the other 2 supermarkets. Another example was “Barramundi”: the marked price of 3 supermarkets were $48/catty and $58/catty, $112.44/kg, and $14.8/100g. After conversion, the per 100g unit price of $48/catty ($7.97) was the lowest, with a difference of 86% compared to the highest unit price of $14.8.

To conclude, consumers should not simply take the marked prices of products for price comparison. The Council recommends supermarkets to make reference to related regulations and experience from overseas jurisdictions and indicate the unit price of products in addition to their marked price. For instance, Australia has implemented Mandatory Unit Pricing Code as early as 2009, which applies to traders who are selling the minimum range of food-based grocery items like bread, butter, fresh fruits, and vegetables, and groceries retailers with more than 1,000 square metres of floor space and online retailers are required to indicate the unit price on shelves and publicity materials. Mandatory or voluntary unit pricing policies were also implemented in some states or regions in the United States. Related unit pricing regulations in Quebec, Canada came into effect in 2001, requiring traders to indicate the unit price of relevant products apart from their selling price. Although there is currently no unit pricing policy established in Hong Kong, the Council urges large supermarket chains to take the lead by providing the unit price (e.g. per 100g or per 100ml) information in standard unit on price tags, and apply the same to products using other unit measurements at a later stage, so that consumers could make a well-informed price comparison between different products and retail stores.

Moreover, consumers may make reference to the Council’s “Online Price Watch” ( for daily updates and price comparison of over 2,200 popular products from 6 major supermarkets, with functions including unit price, top price differences and price drops. The website also displays the price changes of each product in the past 3 months by providing the lowest price trend of the latest 30, 60 and 90 days, which allows consumers to keep up with the price trends without going to the supermarkets.

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