Weights and Measures Acts (UK) facts for kids

The old measurement standards at the Royal Observatory in Greenwich, London. These show a yard, feet, and inches. They were designed so that correct measuring rods would fit perfectly at a temperature of 16.7°C.

Bronze Yard No.11 was the official length standard for the United States from 1855 to 1892. It was a copy of the British Imperial Standard Yard, which was damaged in 1834. This yard was defined by the distance between two fine lines on gold plugs at 16.7°C.

A helium–neon laser at the Kastler-Brossel Laboratory in Paris. Today, Britain's length and volume units are based on how fast light travels in empty space.

Before 2019, Britain's mass units were based on national standards. These were checked against the international kilogram prototype in Paris. This picture shows a copy of that prototype. Now, the modern kilogram is defined by a basic property of matter.

Weights and measures acts are special laws made by the British Parliament. These laws decide how we measure things like weight, length, and volume. They also include older laws from the Kingdoms of England and Scotland, and the medieval Welsh states.

The very first of these laws didn't have official names. Instead, they were known by the king who made them. Today, many important laws are simply called the Weights and Measures Act with the year they were passed.

What Are Weights and Measures Laws?

For over 1,000 years, the United Kingdom has had many laws about weights and measures. These laws do a few key things:

• They list the official weights and measures that people can use.
• They explain how to check and make sure people are using these measurements correctly.
• They describe how the laws can be changed in the future.

Newer laws also allow government ministers to update the rules using special legal documents. Before 1985, these laws mainly focused on how goods were bought and sold. But the Weights and Measures Act 1985 covered much more. It included all the rules from a European Economic Community (EEC) directive about measurements.

As of 2012, the 1985 Act is still the main law in the UK. It was last updated in 2011. These updates don't change the main Act itself. Instead, they add rules for specific areas covered by the Act.

Today, about 200 Trading Standards offices across the country make sure these laws are followed. They are managed by local councils. The National Measurement Office helps by defining units and providing technical equipment for measuring.

What is Statute Measure?

In the past, many units of measurement had different meanings depending on the local area or type of trade. For example, an "acre" might be a different size in one town compared to another.

When a unit had an official, legally defined size in a weights and measures law, it was called the statute measure. So, if someone said "24 acres—statute measure," they meant the official acre size defined by law. This helped avoid confusion.

Units like the acre, mile, and ton often had both official and local definitions. Over time, as laws became stricter, people mostly used the official "statute" sizes. Today, only the "statute mile" still needs to be mentioned to tell it apart from the nautical mile. The term "statute measure" is now mostly used when talking about history.

Metric Units in the UK

The Weights and Measures Act 1897 allowed people to use metric units (like metres and kilograms) in addition to the traditional imperial units (like yards and pounds) for trade. However, there were still rules about what units could be used for certain products.

For example, in 2012, wine served in pubs could only be sold in 125, 175, or 250 millilitre (mL) glasses. Draught beer could only be sold in 1⁄3, 1⁄2, or 2⁄3 pint sizes, or in full pints. Prior to 1973, when the United Kingdom joined the EEC, such specifications were almost all in imperial units.

The European Commission (EC) wanted all member countries to use the same units. So, they issued a rule in 1980 that listed the units to be used for things like business, health, safety, and government. To follow this rule, the Weights and Measures Act 1985 made Trading Standards responsible for all these areas, not just trade. For instance, the Trading Standards Office once criticized hospitals for using inaccurate weighing machines.

To help ease the EC's desired transition from sole use of imperial units to sole use of metric units, the directive permitted the use of what were termed "supplementary indicators"—the continued use of imperial units alongside the metric units catalogued by the directive (dual labelling). The initial intention was to prohibit dual labelling after the end of 1989, with metric units only being allowed after that date. This deadline was later extended several times.

Finally, in 2007, the European Union (EU) confirmed that the UK would be permitted to continue indefinitely to use imperial units such as pints, miles, pounds and ounces as at present. This means you can still buy a pint of milk or beer, and road signs still show distances in miles.

There are still a few cases where imperial units must be used and where metric units are not permitted within the scope of the Weights and Measures Act. These include:

• Pints for selling draught beer and cider.
• Miles and yards for distances on road signage.
• Pints for milk in reusable containers.
• The troy ounce for selling precious metals.

In addition, British law specifies which non-metric units may be used with dual labelling (for example the imperial gallon, but not the US gallon).

Early English Laws

Many early laws from Saxon kings have been lost. But some have survived.

10th Century Laws

King Edgar's Rule (around 959-963)

One important law from King Edgar (2 Edgar c. 8) said:

• "Let one money pass throughout the king's dominion; and that let no man refuse."
• "And let one measure and one weight pass; such as is observed at London and at Winchester."

This law also set the price for a "wey" of wool. Some copies of this law mention "the measure held at Winchester," suggesting there was already a standard ell or yard in use. However, a report from 1821 noted that this law was "never observed," meaning it wasn't really followed.

Laws from the Royal Council

11th Century Laws

King William I (3 William I c. 7, 1068) also made a law about measurements:

• "We ordain and command that the weights and measures, throughout our realm, be as our worthy predecessors have established." This meant he wanted to keep the measurement standards that were already in place.

12th Century Laws

King Richard I (9 Richard I c. 27, 1197) issued the Assize of Measures. This law stated:

• "Woollen cloths, wherever they be made, be made of the same width... of two ells... and of the same good quality."
• "Also the ell shall be the same in the whole realm and of the same length and the ell shall be of iron." This was important because it meant the official ell (a unit of length) should be made of iron to ensure it was always the same.

Laws from Parliament

Laws from Uncertain Dates (13th Century)

Some laws from the 13th century don't have exact dates.

• The Assize of Bread and Ale (sometimes dated to 1267–8) was a law about the size of bread and ale. It said:
  • "The English Peny, called a Sterling, round and without clipping, shall weigh 32 Wheat Corns."
  • "20 pence do make an Ounce, and 12 Ounces one Pound."
  • "8 Pound do make a Gallon of Wine, and 8 Gallons of Wine do make a London Bushel."

• Tractatus de Ponderibus et Mensuris (Treatise on Weights and Measures) was an important document that defined many units. For example, it stated that an ounce weighs 20 pence, and 12 ounces make a pound of London. It also mentioned that a sack of wool should weigh 28 stones. This document also used the word avoirdupois for the first time in England, referring to heavy goods sold by weight.

• The Statute on the Composition of Yards and Perches (around 1266-1303) defined basic units of length:
  • "3 grains of barley dry and round do make an inch."
  • "12 inches make 1 foot."
  • "3 feet make 1 yard."
  • "5 yards and a half make a perch."
  • "40 perches in length and 4 in breadth make an acre."

This law seems to have changed the definitions of the yard, foot, and inch, making them slightly shorter. It also made the rod 16.5 feet long instead of 15 feet.

13th Century Laws

• The Magna Carta (9 Henry III c. 25, 1225) was a very important document. Chapter 25 of this charter stated:
  • "One measure of Wine shall be through our Realm, and one measure of Ale, and one measure of Corn."
  • "One breadth of dyed Cloth... that is to say, two Yards within the lists."
  • "It shall be of Weights as it is of Measures." This meant that weights should also be standard across the country.

14th Century Laws

• In 1340, a law (14 Edw. 3 Stat. 1. c. 12) said that "Bushels and Weights shall be made and sent into every Country." This aimed to spread standard measures.
• The law of 1350 (25 Edw. 3 Stat. 5. c. 9) banned a tricky weighing method called "Auncel." It said that all buying and selling must use "equal Balance" and "right Weight." It also set the weight of a sack of wool at 26 stones, with each stone weighing 14 pounds.
• Another law from 1350 (25 Edw. 3 Stat. 5. c. 10) repeated the Magna Carta's idea that "one Measure shall be throughout England." It specified that all measures like Bushels, Gallons, and Quarts should follow the King's Standard. It also said that grain should be measured "without Heap," meaning level, not piled up.
• The Statute of the Staple (27 Edw. 3 Stat. 2. c. 10, 1353) also stated that there should be "one weight, one measure [of volume], and one [measuring] stick" across the land. It allowed judges to punish people who cheated with measurements.

15th Century Laws

• The Gilding of Silver Act 1414 (2 Hen. 5. Stat. 2. c. 4) was the first law to mention troy weight, a system used for precious metals.
• The Weights, etc. Act 1429 (8 Hen. 6. c. 5) required "Every City and Borough shall have a common Balance and Weight."
• The Weights and Measures Act 1496 (12 Hen. 7. c. 5) gave a detailed definition: "That the Measure of a Bushel contain 8 Gallons of Wheat, and that every Gallon contain 8 pounds of Wheat of Troy Weight, and every Pound contain 12 Ounces of Troy Weight, and every Ounce contain 20 Sterlings, and every Sterling be of the Weight of 32 Corns of Wheat."

16th Century Laws

• The Verdict of the Pyx in 1527 officially changed how gold and silver were weighed. It said that the "pounde Towre shall be no more used" and that "all maner of golde and sylver shall be wayed by the pounde Troye." This made the troy weight pound the standard for precious metals.
• The Sale of Flesh Act 1532 (24 Hen. 8. c. 3) made it law that "Beef, pork, mutton and veal shall be sold by weight called Haver-de-pois." This is the first time the term "avoirdupois" (a system of weights) was used in a law, referring to heavy goods sold by weight.
• The Flax and Hemp Act 1532 (24 Hen. 8. c. 4) defined an acre as "160 perches, and every perch 16-foot and a half."
• The Restriction on Building Act 1592 (35 Eliz. 1. c. 6) defined the statute mile: "A Mile shall contain 8 Furlongs, every Furlong 40 Poles, and every Pole shall contain 16 Foot and an half." This is the official definition of the mile we still use today.

17th Century Laws

• The Measures Act 1670 (22 Cha. 2. c. 8) was the first law to mention the "Winchester bushel" for measuring corn and salt.
• In 1696-97, a law (8 & 9 Will. 3. c. 22. s. 9) gave the first detailed definition of the Winchester bushel: "every round bushel with a plain and even bottom being 18 and a half inches wide throughout and 8 inches deep shall be determined a legal Winchester bushel."

18th Century Laws

• The Taxation (No. 5) Act 1706 (6 Ann. c. 27) defined the wine Gallon: "any Vessel containing 231 cubical Inches and no more shall be deemed... a lawful Wine Gallon." This specific size is now known as the US gallon.

Laws for Great Britain

After England and Scotland united to form Great Britain, new laws were passed for the whole country.

Acts of Parliament

19th Century Laws

• The Weights and Measures Act 1824 (5 Geo. 4. c. 74) was a very important law. It aimed to create "Uniformity of Weights and Measures" across the whole United Kingdom of Great Britain and Ireland. It noted that different measures were still being used, causing "great Confusion and... Frauds." This Act is the origin of Imperial units. It also cancelled almost all older weights and measures laws.
• The Weights and Measures Act 1835 (5 & 6 Will. 4. c. 63) officially set the imperial stone at 14 pounds and the hundredweight at 112 pounds. These were based on older wool measurements.
• The Weights and Measures Act 1855 (18 & 19 Vict. c. 72) was needed because the original physical standards for weights and measures were destroyed in the 1834 burning of Parliament. New copies were made, and this Act made them the new "restored Standards." It declared the "Imperial Standard Pound Avoirdupois" as the main standard for weight.
• The Metric Weights and Measures Act 1864 (27 & 28 Vict. c. 117) made it legal to use the metric system in the UK, but it was not compulsory.
• The Weights and Measures Act 1878 (41 & 42 Vict. c. 49) brought together many different laws about weights and measures. This statute also abolished the troy pound, effective January 1879.
• The Weights and Measures (Metric System) Act 1897 (60 & 61 Vict. c. 46) officially made it legal to use metric weights and measures.

20th Century Laws

• The Weights and Measures Act 1963 (c. 31) replaced many older laws.
• The Weights and Measures Act 1979 (c. 45) introduced the "Average Quantity principle" for packaged goods into UK law for the first time. This means that the average amount of product in a batch of packages must meet the stated quantity.
• The most recent major law is the Weights and Measures Act 1985 (c. 72). This Act brought together many previous laws. It defines the four main units of measurement in the UK:
  • The metre or the yard (which is defined based on the metre) for length.
  • The kilogram or pound (which is defined based on the kilogram) for mass.

The Act also requires that official physical examples, called "United Kingdom primary standards," are kept for these four main units.

The 1985 Act also defines many other units that are multiples or smaller parts of these main units. These include:

• Length: mile, furlong, chain, foot, inch, kilometre, decimetre, centimetre, millimetre.
• Area: acre, square yard, square foot, hectare, decare, are, square metre, square decimetre, square centimetre, square millimetre.
• Volume: cubic metre, cubic decimetre, cubic centimetre, hectolitre, litre, decilitre, centilitre, millilitre, gallon, quart, pint, gill, fluid ounce.
• Mass: tonne, kilogram, hectogram, gram, carat (metric), milligram, hundredweight, cental, quarter, stone, pound, ounce, dram, grain, pennyweight, ounce troy.

Over the years, the 1985 Act has been updated many times. As of January 2020, the metre, yard, kilogram, and pound are still the main defined units. All the imperial units (except pint and troy ounce, which have specific uses) can now be used as "supplementary indications" alongside metric units. This means they can be shown as extra information when selling goods.