Metric packs

Metrication of food retail began in earnest in 1972, when the Government announced plans for legislation to introduce food packaging in round metric sizes, known as “metric packs”.

Metric packs were instrumental in the metrication of the sale of food. They were used in the transition phase, in the 1970s, when package quantities switched from round imperial quantities to round metric quantities, while maintaining the use of dual unit labelling.

A metric pack of cornflakes – 1976

As originally published, the Weights and Measures Act 1963 included a list of basic grocery items which, if pre-packed, could be offered for sale by retail only in a range of prescribed quantities. The purpose of permitting only a limited range of pack sizes for a product was one of consumer protection. It was easier for consumers to compare product prices if manufacturers and stores used the same range of sizes.

The prescribed quantities listed in the Weights and Measures Act 1963, were round imperial amounts. For metrication to proceed, it was necessary to redefine them in round metric amounts.

Government White Paper on Metrication – 1972

Between 1973 and 1978, legislation was passed which set dates for the introduction of new metric pack sizes, and cut-off dates for the withdrawal of corresponding imperial pack sizes.

Pre-packed foods – Specified quantities
Metrication schedule : 1974 – 1978

Food	Metric specified quantities introduced	Imperial specified quantities withdrawn
Pasta	1974-07-01	1978-08-31
Salt	1975-01-01	1978-06-30
Sugar	1975-10-01	1978-04-21
Breakfast cereals	1975-11-01	1978-06-30
Dried vegetables, e.g. beans, peas, lentils	1976-04-01	1978-12-31
Butter and margarine	1977-01-01	1979-07-14
Dried fruits, e.g. raisins, sultanas, dates	1977-01-01	1978-12-31
Flour	1977-07-01	1978-08-31
Biscuits and shortbread	1978-01-01	1978-04-21
Bread	1978-01-01	1978-05-02
Tea and tea bags	1978-04-01	1979-12-31
Chocolate bars (85 g and over)	1978-01-01	N/A
Cocoa and chocolate powders	1978-09-01	N/A

To minimise the impact on consumer protection of having products for sale in two slightly different size ranges at the same time, it was important to keep the transition times between the introduction of the new metric sizes and the withdrawal of the old sizes to a minimum.

During the transition, all packs were required to be marked​ with both metric and imperial weights. Consumers were alerted to look out for the distinctive “METRIC PACK” markings on the new packs, which were mostly about 10% larger than the old imperial packs.

Metric packs information leaflet – 1979

The Metrication Board supported the introduction of the new metric packs with consumer information.

The transition times between the introduction of the new metric sizes and the withdrawal of the old sizes were generally agreed in advance, following consultation with the producers concerned. The crucial factor in most cases was the time it took to re-set machinery, or to install new equipment.

Manufacturers have always periodically re-designed their packaging to cater for changes in fashion or taste, or for other marketing reasons. When faced with the need to cater for the new metric sizes, a variety of solutions was used.

For tins, generally only the height of the tin was changed – this allowed the lids, and the machinery associated with sealing the product, to remain unchanged. Other manufacturers took advantage of the opportunity to introduce more efficient packaging processes, or completely re-designed their packaging for some products. Manufacturers of some powder or flake products were able to pack more product into their existing packets with the ingenious use of additional manufacturing processes which settled the package contents more compactly without crushing.

For each regulated food, legislation stipulated that, one year after the cut-off date for the withdrawal of imperial prescribed sizes, quantity markings on all subsequently produced packages should be “made in metric units, but may, in addition, be in imperial units”. The clear intention was that quantity markings on packaged foods should return to the use of a single system of measurement units as soon as possible following the adoption of rational metric sizes.

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Salt

Pre-packed salt was one of the first foodstuffs to switch to metric prescribed quantities. In 1973, legislation was introduced which permitted the sale of metric packs of salt from 1 January 1975.

A metric pack of salt – 1975

In addition to the already prescribed imperial sizes, the following metric sizes were added to the list of prescribed sizes for pre-packed salt:

125 g, 250 g, 500 g, 750 g, 1 kg, 1.5 kg,
or any multiple of 1 kg up to and including 10 kg,
12.5 kg, 25 kg or 50 kg.

Salt for sale in pack sizes not exceeding 100 g was exempt from the regulations.

From 30 June 1978, the sale of salt in imperial pack sizes ceased to be authorised.

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Sugar

The sale of metric packs of sugar was first permitted on 1 October 1975. Granulated sugar in 1 kg and 500 g metric packs first appeared in the shops in the summer of 1976. Most manufacturers phased out the production of imperial packs by the first half of 1977.

A metric pack of sugar – 1976

In addition to the already prescribed imperial sizes, the following metric sizes were added to the list of prescribed sizes for pre-packed sugar:

125 g, 250 g, 500 g, 750 g, 1 kg, 1.5 kg, 2 kg, 2.5 kg, 3 kg, 4 kg and 5 kg.

Sugar for sale in bags not exceeding 100 g, or exceeding 5 kg was exempt from the regulations.

The metrication of sugar

1975

1976

1980

From 21 April 1978, the sale of sugar in imperial pack sizes ceased to be authorised. By 1980, the use of supplementary imperial markings on bags of sugar had mostly come to an end.

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Breakfast cereals

The sale of metric packs of flaked breakfast cereals, excluding oatflakes, was first permitted on 1 November 1975. Metric packs of oatflake cereals, such as porridge, followed on 1 August 1977.

A metric pack of cornflakes (front and back) – 1976

The following metric sizes were added to the list of prescribed sizes for pre-packed breakfast cereals:

125 g, 250 g, 500 g, 375 g, 750 g, 1 kg, 1.5 kg, and any whole multiple of 1 kg.

Breakfast cereals in pack sizes not exceeding 50 g, or exceeding 10 kg, were exempt from the regulations.

The metrication of cornflakes

When Kellogg’s Corn Flakes switched to round metric pack sizes, the manufacturer was able to modify their packaging machinery to shake down the cereal flakes sufficiently for 10% more product to be packed into the same size cartons. This meant that 500 g of flakes could fit into the same size carton as was previously used for the old 16 oz (454 g) packs.

1975	1976	1977
1978	1979	1980

The metrication of cornflakes serves as an example of how smoothly the switch to metric units could be carried out when it was coordinated with an agreed schedule of cut-off dates backed up with appropriate legislation:

• In their Eighth Report, published in 1977, the Metrication Board reported that, “When cornflakes went metric, customers received 10 percent more in each pack but manufacturers’ prices went up by only 5 percent.” Manufacturers had been able to make savings on packaging when they switched to metric amounts, which they in turn were able to pass on to customers.
• The first metric packs of cornflakes carried some of the most visibly distinctive round metric weight markings, which served to inform customers both of the new rational metric pack sizes, and of the change that would soon affect all food packaging.
• The detailed customer information on the back of the initial metric packs of cornflakes packets would have been seen by millions of families at the breakfast table in 1976.
• At the earliest opportunity allowed by the legislation, manufacturers were able to drop the dual unit labelling and complete the metrication process by switching to metric-only labelling.

The metrication of Special K

Unlike Kellogg’s Corn Flakes, most cereals required larger size cartons to accommodate the new metric prescribed quantities. In 1976, the width and height of the new 375 g metric packs of Kellogg’s Special K remained more or less the same as the old 12 oz (340 g) size, but the depth was increased from 63 mm to 70 mm.

1973

1976

1977

The tops of metric packs of cereals tended to show the contents in metric only, whilst dual units were used on the front and sides of the packet.

On 30 June 1978, the sale of breakfast cereals in imperial pack sizes ceased to be authorised, with the exception of oatflake cereals whose sale in imperial sizes remained authorised until 31 October 1978.

For most breakfast cereals, the use of supplementary imperial markings ended in 1980.

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Butter and margarine

Metric packs of butter, margarine and other edible fats were first permitted on 1 January 1977.

1979

1980

In addition to the already prescribed imperial sizes, the following metric sizes were added to the list of prescribed sizes for pre-packed butter, margarine, and other edible fats:

50 g, 125 g, 250 g, 500 g,
any whole multiple of 500 g up to 4 kg,
and thereafter any whole multiple of 1 kg up to 10 kg.

Edible fats in packs not exceeding 25 g, or exceeding 10 kg, were exempt from the regulations.

Margarine in 250 g and 500 g packs first appeared on retailers’ shelves in February 1979, with metric packs of butter following in July. Fats such as lard and dripping began the changeover in September 1979.

From 14 July 1979, imperial pack sizes of butter and margarine ceased to be authorised. Imperial pack sizes of lard, dripping and cooking fat ended on 29 September 1979, with shredded suet following on 31 December 1979.

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Flour

The sale of metric packs of flour was introduced on 1 July 1977. To aid shoppers, the Metrication Board produced a price comparisons card.

Flour in metric packs – 1977

In addition to the already prescribed imperial sizes, the following metric sizes were added to the list of prescribed sizes for pre-packed flour:

125 g, 250 g, 500 g, and any whole multiple of 500 g.

In the case of cornflour, a further two metric sizes were added:

375 g and 750 g.

Flour for sale in bags not exceeding 50 g, or exceeding 10 kg, was exempt from the regulations.

From 31 August 1978, the sale of flour in imperial pack sizes ceased to be authorised.

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Tea

The sale of metric packs of tea was first permitted on 1 April 1978.

1977

1978

In addition to the already prescribed imperial sizes, the following metric sizes were added to the list of prescribed sizes for pre-packed tea:

50 g, 125 g, 250 g, 500 g, 750 g, 1 kg, 1.5 kg, 2 kg, 2.5 kg, 3 kg, 4 kg and 5 kg.

Tea in package sizes not exceeding 25 g, or exceeding 5 kg were exempt from the regulations.

1977

1978

From 31 December 1979, the sale of tea in imperial pack sizes ceased to be authorised. The use of supplementary imperial markings on metric packets of tea ended shortly afterwards.

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Chocolate

When the metrication of food packaging began, it became inevitable that the production of chocolate would also eventually switch to the use of round metric sizes.

An early metric chocolate bar – 1974

To facilate a smooth transition to metric sizes, and to avoid a situation developing where chocolate bars in round imperial sizes continued to be sold alongside chocolate in round metric sizes, chocolate was added to the list of foods required to be sold only in a range of prescribed sizes.

As part of this process, from 1 August 1975, all pre-packed chocolate bars, of 50 g and over, were required to be marked with metric weights.

1973

1974

In August 1977, legislation was introduced to add pre-packed chocolate products to the list of foods required to be made for sale only in a range of prescribed sizes.

From 1 January 1978, all chocolate bars weighing not less than 85 g, and not more than 500 g, were required to be made for sale only in one of the following metric weights:

85 g, 100 g, 125 g, 150 g, 200 g, 250 g, 300 g, 400 g or 500 g.

1976	1976
1978	1979

Most producers adapted their ranges to the new prescribed sizes well in advance of the cut-off date, and by the end of 1976, most of the affected products were available in metric sizes.

As there had been no previously prescribed imperial pack sizes, it was not deemed necessary for the words “METRIC PACK” to appear on the new metric chocolate bar wrappers.

1980

1982

Chocolate bars with wrappers marked in metric-only first appeared for sale in 1980. However, some chocolate products continued to show supplementary imperial markings alongside their metric weights until the mid 1980s.

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Cocoa powder

In August 1977, legislation was introduced to add cocoa powder to the list of pre-packed foods required to be made for sale only in a range of prescribed sizes.

1976

1978

From 1 September 1978, all pre-packed cocoa powder and drinking chocolates were required to be sold only in one of the following metric weights:

50 g, 75 g, 125 g, 250 g, 500 g, 750 g or 1 kg.

Pack sizes of less than 50 g, or exceeding 1 kg were exempt from the regulations.

1977

1978

Since there had previously been no imperial sizes prescribed for pre-packed cocoa powder, there was no legal requirement for the new metric sizes to be marked with the words “METRIC PACK”. However, manufacturers generally chose to do so, as this helped customers to realise that pack sizes had increased slightly.

A metric pack of drinking chocolate – 1978

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The abolition of the Metrication Board

Towards the end of 1978, as the date of the next General Election grew nearer, the Government of the day hesitated to introduce the legislation necessary to switch the remaining imperial specified quantity foods to metric prescribed sizes. It had been thought politically expedient to wait until the new Parliament to complete metrication. However, the Government lost the 1979 election, and on 14 November 1979 the new Government announced the abolition of the Metrication Board.

From 1979 onwards, metric sizes continued to be added to the prescribed sizes of some of the remaining imperial-only specified-quantities foods, but all plans for the further withdrawal of prescribed imperial sizes of foods were postponed indefinitely.

Where metric sizes had not yet been prescribed, new metric sizes were added to the existing prescribed imperial sizes for the following foods:

Pre-packed foods – Specified quantities
Metrication schedule : 1979 onwards

Food	Metric specified quantities introduced	Imperial specified quantities withdrawn
Potatoes	1978-06-01	Not withdrawn
Coffee extracts, e.g. instant coffee	1979-07-01	1989-01-01
Coffee, e.g. ground coffee, coffee bags	1982-01-01	Not withdrawn
Milk	1980-01-01	Not withdrawn
Rice and other grain products, e.g. sago, tapioca, semolina	1982-01-01	Not withdrawn

Although there were now no plans to withdraw the remaining similar imperial sizes from the prescribed sizes lists, all new metric packs were no longer required to show “METRIC PACK” distinguishing markings.

For the affected foods, the purpose of having prescribed pack sizes had been fundamentally undermined. Consumer protection would be adversely affected for many years by the prolonged existence of different pack sizes that were superficially similar.

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Potatoes

The sale of potatoes in metric pack sizes was first permitted on 1 June 1978.

In addition to the already prescribed imperial sizes, the following metric sizes were added to the list of prescribed sizes for pre-packed potatoes:

500 g, 1 kg, 1.5 kg, 2 kg, 2.5 kg,
and any whole multiple of 2.5 kg up to and including 15 kg,
20 kg, and 25 kg.

Potatoes for sale in bags less than 175 g, or exceeding 25 kg, were exempt from the regulations.

In the absence of direction from government, processors saw little reason to make a rapid switch to metric pack sizes. Potatoes continued to be sold loose by the pound, and pack sizes of 2 lb could superficially appear to be better value than 1 kg packs.

It would not be until some time after 2000, when loose potatoes were first sold by metric weight, that rationalisation of pre-packed potatoes would take place in earnest.

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Coffee

The sale of instant coffee in metric pack sizes was introduced on 1 July 1979.

A metric pack of coffee – 1980

In addition to the already prescribed imperial sizes, the following metric sizes were added to the list of prescribed sizes for pre-packed instant coffee:

50 g, 100 g, 200 g, 300 g, 500 g, 750 g, 1 kg, 1.5 kg, 2 kg, 2.5 kg, 3 kg,
and any whole multiple of 1 kg.

Instant coffee in pack sizes not exceeding 25 g, or exceeding 10 kg, was exempt from the regulations.
 

A metric pack coffee jar label – 1979

Manufacturers were quick to adopt the 100 g module already in common use on the continent. The new regulations allowed manufacturers to switch to a single size range for domestic and export markets. The switch meant dropping the 227 g (8 oz) size in favour of the slightly smaller 200 g size, and replacing the 113 g (4 oz) size with the slightly smaller 100 g size.
 

A metric pack coffee jar label – 1980
 

A metric-only coffee jar label – 1981

On 1 January 1982, when coffee beans, ground coffee, and coffee bags were first added to the list of foods for retail in specified quantities only, they were given a different set of metric prescribed sizes from those already in operation for instant coffee and other coffee extracts. A module size of 125 g was chosen rather than the 100 g module size adopted for instant coffee.

To make matters worse, two similar size ranges were prescribed for the new items simultaneously – one metric, and one imperial:

75 g, 125 g, 250 g, 500 g, 750 g, 1 kg,
and any whole multiple of 500 g.
1 oz, 2 oz, 4 oz, 8 oz, 12 oz, 1 lb, 1½ lb,
and any whole multiple of 1 lb.

Coffee in pack sizes not exceeding 25 g, or exceeding 5 kg, was exempt from the regulations.

If consumers didn’t study weight markings carefully, a pack size from one range could easily be mistaken for a pack size from the other, thus defeating the whole purpose of prescribed sizes.

The lack of available 100 g and 200 g prescribed sizes for ground coffee and coffee beans, together with the lack of any cut-off date for imperial prescribed sizes, gave little incentive for local manufacturers to switch to round metric pack sizes for ground coffee and coffee beans. Meanwhile, imported ground coffee in round metric sizes was of course permitted. So, shoppers were left with a potential plethora of different pack sizes for coffee, and the consumer protection purpose of having a small restricted range of prescribed sizes was undermined.

The imperial prescribed sizes for instant coffee were quietly dropped from the regulations with effect from 1989.

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Milk

The sale of metric packs of liquid milk was introduced on 1 January 1980.

In addition to the already prescribed imperial sizes, the following metric sizes were added to the list of prescribed sizes for pre-packed milk:

200 ml, 250 ml, 500 ml, 750 ml, 1 L, 2 L, and thereafter any whole multiple of 500 ml.

Milk in pack sizes not exceeding 50 ml was exempt from the regulations.

When plastic cartons of milk first appeared in supermarkets in 1980, they were one litre in size. Hitherto, milk had mostly been sold in returnable one-pint glass bottles by home delivery, with only a small amount of milk being sold in pint and half-pint cardboard cartons in supermarkets.

In the years that followed, home deliveries of milk declined, and larger plastic cartons of milk became available in supermarkets. The failure to remove imperial sizes from the list of prescribed sizes for milk, led to a bewildering range of sizes of milk cartons being available, which in turn made it increasingly difficult for consumers to make price comparisons.

Milk in similar imperial and metric pack sizes – 2019

The confusion still exists to this day. More than 40 years after the introduction of metric pack sizes, milk in round imperial sizes is still sold alongside metric packs.

Today, milk is commonly available in all of the following sizes:

500 ml, 568 ml (1 pint), 1 L, 1.136 L (2 pints), 2 L, 2.272 L (4 pints) and 3.408 L (6 pints).

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Imperial remnants

It is also notable that no metric sizes were ever added to the following foods sold in prescribed sizes:

Food	Metric specified quantities introduced	Imperial specified quantities withdrawn
Honey	Not introduced	Not withdrawn
Jam, marmalade, preserves	Not introduced	Not withdrawn
Syrup, treacle, molasses	Not introduced	Not withdrawn

This meant that the sale of the above foods had to remain in round imperial amounts, even though most other common “food basket” items had already switched to rational metric sizes.

Years later, when supplementary imperial units were dropped from the metric weight markings on these products, we were left with a legacy of some odd-looking product sizes. The 454 g jars of jam and 454 g tins of syrup, that can still be found on supermarket shelves, look quite out of place amongst today’s range of food in modern rational metric package sizes.

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Value for money

On the whole, the switch to metric prescribed sizes lead to slightly larger pack sizes. This in turn lead to an overall reduction in the number of packs needed for a given quantity of food, and savings in packing costs.

In 1977, a Price Commission report confirmed that metrication did not, on a weight for weight basis, lead to increases in the retail prices of the main ‘shopping basket’ foods. Indeed, six brand name foods were better value for money in grams and kilograms than in ounces and pounds.

Deregulation of pack sizes

From 11 April 2009, all specified quantities for pre-packed foods were deregulated, with the exception of wines and spirits.

From a consumer protection point of view, pack sizes in specified quantities were no longer needed, following the introduction in 2004 of the requirement for the display of unit pricing on shop shelving for all pre-packed foods with quantity markings.