Food and drink

METRICATION:  99% complete
	Metric	Non-metric
	All foods sold loose are weighed and priced in kilograms	Most milk is still sold in round imperial quantities
	All quantity-marked pre-packed foods are marked with metric units
	All pre-packed foods are sold with metric unit pricing

Measurement units

Quantity	Old unit	Metric unit	Symbol
weight	ounce	gram	g
large weight	pound, hundredweight	kilogram	kg
volume	fluid ounce, pint	millilitre	ml
large volume	pint, quart, gallon	litre	L

Metrication

In the 2020s, we are all used to seeing food labelled, weighed, and sold in metric units. The vast majority of pre-packed foods are labelled exclusively in metric units, and come in pack sizes that are round metric amounts. Metric unit pricing of foods sold loose, and of pre-packed foods, also allows consumers to compare prices easily, both between different stores, and between different pack sizes within the same store.

These benefits have only been with us for about twenty years. They were arrived at only after a prolonged and unduly tortuous period of transition from the old imperial units of measure.

In the 1960s, it was decided that food should switch from being weighed and sold in pounds, ounces and other imperial units, to being weighed and sold in modern metric units. The move, prompted by the needs of British businesses operating in an increasingly globalised market place, was to be part of a coordinated switch to the use of metric units across all sectors of the economy.

The change could not be carried out overnight, as was the case with the decimalisation of currency, but it was still desirable for the duration of the change over to be kept to a minimum. Commencing in 1965, the Government anticipated that the national metrication programme would be largely complete by 1975.

In the case of food, it was quite possible for the change to metric units to have been carried out at minimum cost within a period of 2 years. In the event however, it was not until more than 30 years after starting the process, that the metrication of the food sector could be said to be largely complete.

The setbacks and delays along the way were political, rather than technical in nature. A lack of commitment by successive governments to carry through decisions, and a failure to properly consider consumer protection issues, allowed a situation to develop where, for a period of more than 20 years, foods were sold alongside each other using two different measurement systems.

Pre-packed foods

The Weights and Measures Act 1963 included a list of basic grocery items, such as sugar, flour, tea, butter and margarine, 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 standard range of sizes.

Metric packs

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. Plans for the necessary changes to legislation were announced in 1972, in the Government’s White Paper on Metrication. The new round metric sizes would be called “metric packs”.

A metric pack of sugar – 1976

Between 1973 and 1979, legislation came into effect setting dates for the introduction of new metric pack sizes, and for the withdrawal of corresponding imperial pack sizes. The transition times between the introduction of the new metric sizes and the withdrawal of the old sizes were kept to a minimum, and were agreed in advance following consultation with the manufacturers concerned. The crucial factor in most cases was the time it took to re-set machinery, or to install new equipment.

The Metrication Board supported the introduction of new metric packs with publicity and consumer information. During the transition, all packs were required to be marked​ with both metric and imperial units. The new packs were also marked distinctively with the words “METRIC PACK”, to distinguish them from the old imperial packs, which were mostly smaller in size.

Metrication information on the back of a metric pack of cornflakes – 1976

Manufacturers also provided consumer information on their new packaging. The information on the back of cornflakes packets was a highly visible example that would have been seen by millions of families at the breakfast table in 1976.

By the beginning of 1980 over 95 per cent by value of these foods was made up in rounded metric quantities.

However, on 30 April 1980 the Metrication Board was abolished before all prescribed quantities had been switched to metric sizes. The task of converting the remaining prescribed quantities to metric sizes was put on indefinite hold. This left food stores with a mixture of metric and imperial pack sizes. Most notably, coffee, jams, and syrups were in imperial, with tea, sugar, bread, margarine and breakfast cereals in metric.

During a debate in the House of Lords, shortly after the announcement of the abolition of the Metrication Board, Baroness Seear commented on the situation:

Baroness Seear, 31 January 1980

The table below shows the mixture of metric and imperial units that were in place 10 years after it had originally been envisaged that all foods would be sold in metric units.

Specified quantities – 1989

Food	Prescribed sizes	Measurement units
Rice, sago, semolina, tapioca, barley kernels, pearl barley	125 g, 250 g, 375 g, 500 g, or a multiple of 500 g	metric and imperial
	4 oz, 8 oz, 12 oz, 1 lb, 1½ lb, or a multiple of 1 lb
Biscuits	100 g, 125 g, 150 g, 200 g, 250 g, 300 g, or a multiple of 100 g	metric
Bread (whole loaf exceeding 300 g)	400 g or a multiple of 400 g	metric
Cereal breakfast foods	125 g, 250 g, 375 g, 500 g, 750 g, 1 kg, 1.5 kg, or a multiple of 1 kg	metric
Chocolate bars (85 g and more)	85 g, 100 g, 125 g, 150 g, 200 g, 250 g, 300 g, 400 g, or 500 g	metric
Cocoa products (cocoa powder, drinking chocolate)	50 g, 75 g, 125 g, 250 g, 500 g, 750 g and 1 kg	metric
Coffee (ground coffee, coffee mixtures, coffee bags)	75 g, 125 g, 250 g, 500 g, 750 g, 1 kg, or a multiple of 500 g	metric and imperial
	2 oz, 4 oz, 8 oz, 12 oz, 1 lb, 1½ lb, or a multiple of 1 lb
Instant coffee, coffee and chicory extracts consisting of solid and paste coffee, chicory products	50 g, 100 g, 200 g, 300 g, 500 g, 750 g, 1 kg, 1.5 kg, 2 kg, 2.5 kg, 3 kg, or a multiple of 1 kg	metric
Dried fruits (apples, apricots, currants, dates, figs, muscatels, nectarines, peaches, pears, prunes, raisins, sultanas, dried fruit salad)	125 g, 250 g, 375 g, 500 g, 1 kg, 1.5 kg, 7.5 kg, or a multiple of 1 kg	metric
Dried vegetables (beans, lentils, peas)	125 g, 250 g, 375 g, 500 g, 1 kg, 1.5 kg, 7.5 kg, or a multiple of 1 kg	metric
Edible fats (butter, margarine, low fat spreads, lard)	50 g, 125 g, 250 g, 500 g, or a multiple of 500 g up to and including 4 kg, or thereafter a multiple of 1 kg up to 10 kg	metric
Flour	125 g, 250 g, 500 g, or a multiple of 500 g, and in the case of cornflour, in addition 375 g and 750 g	metric
Honey	2 oz, 4 oz, 8 oz, 12 oz, 1 lb, 1½ lb, or a multiple of 1 lb	imperial
Jam, marmalade, jelly preserves	2 oz, 4 oz, 8 oz, 12 oz, 1 lb, 1½ lb, or a multiple of 1 lb	imperial
Milk	200 ml, 250 ml, 500 ml, 750 ml, 1 L, 2 L, or there after a multiple of 500 ml	metric and imperial
	⅓ pt, ½ pt, or a multiple of ½ pt
Molasses, syrup, treacle	2 oz, 4 oz, 8 oz, 12 oz, 1 lb, 1½ lb, or a multiple of 1 lb	imperial
Oat products	125 g, 250 g, 375 g, 500 g, 750 g, 1 kg, 1.5 kg, or a multiple of 1 kg	metric
Pasta	125 g, 250 g, 375 g, 500 g, or a multiple of 500 g	metric
Potatoes	500 g, 1 kg, 1.5 kg, 2 kg, 2.5 kg, or a multiple of 2.5 kg up to and including 15 kg, 20 kg, or 25 kg	metric and imperial
	8 oz, 12 oz, 1 lb, 1½ lb, or a multiple of 1 lb
Salt	125 g, 250 g, 500 g, 750 g, 1 kg, 1.5 kg, or a multiple of 1 kg up to and including 10 kg, 12.5 kg, 25 kg, or 50 kg	metric
Sugar	125 g, 250 g, 500 g, 750 g, 1 kg, 1.5 kg, 2 kg, 2.5 kg, 3 kg, 4 kg, or 5 kg	metric
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, or 5 kg	metric

Pre-packed food – Metric unit marking

From 1 January 1978, all pre-packed foods, which were required to be marked with quantity by measurement, were required to be marked with both metric and imperial units.

From 1 February 1979, for any pre-packed food whose sale was permitted only in specified quantities;

• if a pack was made up according to a metric specified quantity, then it was required to be marked in both metric and imperial units, even if no range of imperial specified quantities exists.
• if a pack is made up according to an imperial specified quantity, then it was required to be marked in both metric and imperial units, even if no range of metric specified quantities existed.

The above requirements remained in place until 31 December 1979.

From 1 January 1980, all pre-packed foods, which were required to be marked with quantity by measurement, were required to be marked in metric units. Supplementary imperial indications were permitted, but not required.

In effect, 1 January 1980 was M-day for food packaging. For all pre-packed foods that were not already required to be sold in prescribed metric sizes, the legal measurement unit had switched from imperial to metric.

The Weights and Measures (Marking of Goods and Abbreviations of Units) (Amendment) Regulations 1977

Pre-packed foods – the average system of quantity marking

On 1 January 1980, legislation came into effect permitting “average” quantity marking for pre-packed foods made up in pre-determined constant quantities, instead of the previous “minimum” quantity declarations.

For the purpose of the regulations, “packaged goods” were products that met all of the following requirements:

• Sold sealed;
• Between 5 g and 25 kg, or 5 mL and 25 L;
• The same weight, or volume, as other products of the same type;

The labelling of packaged goods were required to comply with one of the following two systems:

Minimum system

Every package must contain at least the quantity displayed on the label. Each package can contain more than the label says, but not less.

Average system

If products are packed to using the average system, they must comply with the following three rules:

• The contents of the packages must not be less, on average, than the weight on the label;
• Only a small number of the packages can fall below a certain margin of error, known as the tolerable negative error (TNE);
• No package can be underweight by more than twice the TNE;

The TNE for a package is dependent on its declared weight or volume.

Manufacturers and packers were encouraged to adopt round metric quantities when making the necessary adjustments to comply with the new regulations. The technical specifications for the average system use metric units exclusively, so adopting round metric quantity declarations simplified matters.

Tolerable negative errors were defined in terms of grams or millilitres, or as a percentage of the nominal quantity (in which case that amount would be rounded up to the nearest 0.1 g or 0.1 ml).

Tolerable negative error (TNE)

Nominal quantity in grams or millilitres	Tolerable negative error
	As a percentage of nominal quantity	g or ml
5 to 50	9	–
50 to 100	–	4.5
100 to 200	4.5	–
200 to 300	–	9
300 to 500	3	–
500 to 1000	–	15
1000 to 10 000	1.5	–
10 000 to 15 000	–	150
above 15000	1	–

The upper and lower quantity limits to which the regulations applied were also specified in metric units only.

The abolition of the Metrication Board

In October 1979, the Metrication Board submitted their Report on the Change to Metric in the Retail Trade to the Minister of State for Consumer Affairs.

The report stated that retail trade was reluctant to complete the switch to metric on a purely voluntary basis, mainly on account of metric prices appearing to be higher than imperial because, in general, round metric quantities are larger than imperial.

However, all sectors of retail trade had said they were willing to accept an early, orderly, time-tabled programme with supporting legislation to guarantee fair trade competition, and with publicity to help consumers during the transition.

The conclusion was that with out some form of legislative approval by the Government for a new programme agreed by trade and consumer organisations, metrication in the retail sector would not be achieved in the near future.

However, the report’s recommendations were largely ignored, and on 14 November 1979, the Minister for Consumer Affairs announced the abolition of the Metrication Board, and stated that future metrication would be on a voluntary basis only.

The paradox of resisting an orderly metrication programme, was that it ensured that metrication remained with us for decades rather than being over within a few years. Delaying the programme only served to increase resistance to change, and to prolong consumer confusion.

There was also no desire to reverse metrication, which was never going to be a practical proposition, owing to the enormous costs that would have been involved, and the disadvantages of using units that were now unfamiliar to the younger generation, and which didn’t even relate to each other in a logical manner. Manufacturers would have been severely disadvantaged if they had been required to revert to separate product lines for domestic and export markets.

End of imperial units

Metric units had been legal for trade since at least 1897. However, in practice dual systems of weights and measures were not used for most trade purposes until the metrication programme commenced in the 1960s and 1970s.

The purpose of the metrication programme had been to replace the previous collection of archaic units with international standard easy-to-use units. The simultaneous use of dual systems of weights and measures had only ever been envisaged as a short term necessity during the transition to the sole use of metric units. In 1965, the expectation had been that the entire process would be completed in no more than 10 years.

Over a period of many years, beginning well before the 1970s, legislation had gradually reduced the number of imperial units that were authorised for trade. This process continued during the metrication programme of the 1970s:

Withdrawal of authorisation of imperial units

Imperial unit	Date withdrawn
chain, furlong, nautical mile, rood, cubic yard, bushel, dram, cental	1978-04-27
hand, square inch, square mile, cubic inch, cubic foot, cran, grain, stone, quarter, hundredweight, ton	1980-09-01

However, by the early 1990s, it was apparent that the inevitable end of the use of all remaining imperial units was well over due. The metric transition period had lasted so long that the operation of two dual systems was becoming engrained, and was in danger of permanently damaging a major principle of consumer protection that had existed since Magna Carta, namely that a single standard of weights and measures should apply for all trade purposes. In 1994 and 1995, legislation was passed that would finally end the use of imperial units for most official purposes.

From 1 October 1995, all remaining imperial units ceased to be authorised for economic, public health, public safety or administrative purposes, with the following exceptions:

^*the acre subsequently ceased to be authorised on 1 January 2010

Additionally, the following uses were permitted until the end of 1999:

 
The legislation did not end the use of dual unit labelling, but importantly, it did remove the potential legal ambiguity of labelling goods with two different authorised units. The metric unit was now the sole authorised unit, and any additional imperial unit was now permitted only as a supplementary indication.

Foods pre-packed in variable weights

Following the abolition of the Metrication Board in 1980, and the scrapping of the draft legislation that had been drawn up to complete metrication in the food sector, there were two main areas that remained imperial. These were the weighing and unit pricing of loose foods, and the quantity marking of pre-packed foods of variable weights. While most other foods had gone metric by 1980, these foods continued to be sold in imperial for the next 15 years.

From 1 October 1995, foods pre-packed in variable weights such as cheese and meats, were required to be sold in metric units. Imperial units were no longer authorised, but were permitted to be used only as supplementary indications.

This long-delayed change meant that it was now easier to compare value for money across a wider range of products. The change over was accompanied by information leaflets for consumers, produced by the Department of Trade and Industry, and by major supermarkets.

Shopping metrication leaflet – 1995

In practice, however, this change had little effect on shoppers, many of whom purchase variable weight packs according to the pack price, or the appearance of the contents – both of which were unaffected by the switch to metric.

One obvious advantage of metric pricing for consumers is the increased ease of checking pack prices.

Imperial unit pricing	Metric unit pricing

With the old imperial pricing label, calculating the pack price was far from straight forward. The net weight in ounces and fractions had to be converted to decimal pounds before it could be multiplied by the unit price (in £/lb).
e.g.

6¾ oz × £2.83/lb	=
6.75 oz × £2.83/lb	=
(6.75 oz ÷ 16 oz/lb) × £2.83/lb	=
0.422 lb × £2.83/lb	= £1.19

However, with metric pricing labels, it is straight forward to calculate the pack price (in £). One has only to multiply the net weight (in kg) by the unit price (in £/kg).
e.g.

0.19 kg × £6.24/kg

= £1.19

Before the introduction of decimal money in 1971, the equivalent calculation using £sd and lb/oz could be so cumbersome as to be impractical for most consumers.

More than 25 years later, the advantages of metric pricing are so plain to see that today it is difficult to comprehend why the changes were delayed for so long.

Foods sold loose

The most common foods that are bought loose are fruit and vegetables, raw and cooked meat, fish, poultry and cheese. Before 2000, these foods were weighed and priced in pounds and ounces.

From 1 January 2000, all foods sold loose were required to be weighed and priced in kilograms or grams. For many traders this necessitated the purchase of new metric-compliant weighing equipment. Many traders switched to metric weighing before the deadline. The use of pounds and ounces as a supplementary indication, in addition to kilograms and grams, was permitted.

Dual unit pricing errors – 2006

Again, the practice of dual unit-pricing was only ever intended to be temporary. The images above, taken 6 years after the introduction of metric unit pricing, show how easily unit pricing errors can occur when dual units are used. In these instances, when a metric unit price was needed to be adjusted quickly, the adjustment to the supplementary unit price was overlooked.

Pre-packed food – metric unit pricing

From 18 March 2000, all shops, with a floor area of at least 280 m², were required to display metric unit prices for all pre-packaged foods required to be marked with quantity, or to be made up in a prescribed quantity.

In practice, this meant that standard metric unit prices were now shown on shelf labels alongside most pack prices.

A “unit price” meant the price, including VAT, for one kilogram, one litre, one metre, one square metre or one cubic metre of a product.

Quantity	Default unit
weight	kilogram
volume	litre
	cubic metre
area	square metre
length	metre

Additionally, certain named products were required to be priced using units of quantity different from the default units, such as 100 g or 100 ml. Again, these were exclusively metric. The schedule of unit prices was updated in 2004, and is shown in the table below:

Product	Units of quantity
Flavouring essences	10
Food colourings	10
Herbs	10
Spices	10
Biscuits and shortbread	100 (except where sold by number)
Bread	100 (except where sold by number)
Breakfast cereal products	100 (except where required to be quantitymarked by number)
Chocolate confectionery and sugar confectionery	100
Coffee	100
Cooked or ready-to-eat fish, seafoods and crustacea	100
Cooked or ready-to-eat meat including game and poultry	100
Cream and non-dairy alternatives to cream	100
Dips and spreads excluding edible fats	100
Dry sauce mixes	100
Fresh processed salad	100
Fruit juices, soft drinks	100
Ice cream and frozen desserts	100
Pickles	100
Pies, pasties, sausage rolls, puddings and flans indicating net quantity	100 (except where sold by number)
Potato crisps and similar products commonly known as snack foods	100
Preserves including honey	100
Ready to eat desserts	100
Sauces, edible oils	100
Soups	100
Tea and other beverages prepared with liquid	100
Waters, including spa waters and aerated waters	100
Wines, sparkling wine, liqueur wine, fortified wine	750

The figure denoting the relevant units of quantity in the second column of the table for the corresponding product in the first column of the table refers to:

• grams, where the product is sold by weight;
• millilitres, where the product is sold by volume; and
• either grams or millilitres, as indicated by the manufacturer of the product, where the product is permited to be sold by either weight or volume.

All prices and unit prices are in sterling.

The introduction of standard metric unit pricing for the vast majority of foods for retail sale, gave consumers the power to compare prices not only between standard pack sizes, but across packs of any size. Mental arithmetic was no longer required to work out the value-for-money of pre-packed food products.

Pre-packed food – dual unit labelling

When the metrication programme began, marking pre-packed foods with both metric and imperial units to show the same quantity was only ever intended to be a short-term practice during the metric transition. Apart from the reduced clarity and the added clutter on a product label, errors can occur in the conversion process.

Dual unit conversion error – 2006

The example above shows a dual unit conversion error on a pre-packed food product in 2006, more than 30 years after the metric transition of food started. Such instances are a direct consequence of the extremely slow pace of metrication in the food sector.

Pre-packed food – dual unit pricing

Although imperial unit pricing had now ended, its use was permitted as a supplementary indication:

The Price Marking Order 2004

However, because imperial unit pricing was optional, it was of no practical value to consumers. Unit pricing only works as a consumer protection tool if shoppers can use the same figure to compare prices in all shops, and not all shops used supplementary imperial unit pricing.

Supplementary imperial unit pricing also adds clutter to shelf labels, and for a number of years was often used as an obfuscation device with the aim of making a unit price look cheaper.

Imperial supplementary unit pricing – 2006

A shelf label with no less than 6 unit prices – 2006

Sometimes, an imperial supplementary unit price would be used purely to make a pre-packed food look cheaper. In the above example from 2006, there was no way for a consumer to buy one pound of the pre-packed kilogram-bag of sugar. And, as sugar has been sold exclusively in metric pack sizes since 1978, there could be no pretending that the imperial unit price had been added to help customers unfamiliar with sugar in kilograms.

A deadline planned for 2009, for the ending of dual unit pricing was cancelled in 2007. There is currently no cut-off date scheduled for the authorised use of supplementary indications. Today, in the 2020s, most supermarkets restrict the use of supplementary unit pricing to a few select items, or have completely eliminated their use altogether.