The editor remembers this slogan from his time in the UK construction industry in the early 1970’s. Almost half a century later, Ronnie Cohen gives real-world examples of metric quantities that may help those who are not as familiar with metric units as they might wish.
Familiarity with metric units comes with usage. However, the continuing presence of imperial units in some areas discourages Britons from thinking clearly and consistently in a single measurement system.
“Think metric and don’t convert” is the central theme of UKMA’s ThinkMetric website, currently under review. In this article, we will look at how we can visualise metric quantities with real-world objects. For example, many Britons seem to have difficulty in making sense of their and others’ personal height and weight in metric units but seem to have no trouble understanding weather reports with temperatures in Celsius. Clearly, the predominant use of Celsius indicates that we can adapt to the use of metric units when given an opportunity to become familiar with them.
|Object||Approximate Length of Typical Item|
|Thickness of a compact disc||1 millimetre|
|Diameter of a shirt button||1 centimetre|
|Length of AA battery||5 centimetres|
|Diameter of a compact disc||12 centimetres|
|Size of A4 sheet of paper||20 x 30 centimetres|
|Height of a door knob from the ground||1 metre|
|Length of adult-sized bed||2 metres|
|Distance between start and finish line for a sprint race on athletics track||100 metres|
|Height of the Elisabeth Tower aka ‘Big Ben’||92 metres|
|Central span of the Forth road bridge||1 kilometre|
|Length of Great Britain||1000 kilometres|
Long distances are normally expressed in miles because that is what is used on British roads, even when the original source uses kilometres. Journalists fear that their audience will not understand distances expressed in kilometres. As long as distances and speeds are expressed in miles on British roads, Britons will continue to think in miles and shun relatively unfamiliar kilometres.
Mass or ‘weight’
|Object||Approximate Mass of Typical Item|
|Paper clip||1 gram|
|AA battery||25 grams|
|Bar of soap||100 grams|
|Small tub of margarine||250 grams|
|Regular bag of sugar||1 kilogram|
|Typical motor car tyre||7 kilograms|
Britons normally express their personal weight in stones and pounds but use grams and kilograms for cooking recipes, weights in a gym, food products, DIY products and household goods. Yet when we express our personal weight in kilograms to other Britons, they will most likely ask us for conversions to stones and pounds. You can help them by refusing.
|1 m/s or 3.6 km/h||Average human walking speed|
|20 km/h||Easy cycling speed on a bicycle|
|50 km/h||Cars on main roads in built-up areas|
|90 – 100 km/h||Cars on motorways|
|200–300 km/h||High speed train|
|360 km/h||Racing car|
|1000 km/h||Cruising speed of a passenger jet aircraft|
The use of kilometres in the UK is relatively unfamiliar because of the use of miles for distance and speed on British roads. The continued use of imperial units on traffic signs and other public signage prevents Britons thinking consistently in metric units. That requires action from government to complete the changeover and banish imperial units from our roads.
|1 square metre||The area covered by a large umbrella|
|100 square metres||Typical house or large flat|
|1 hectare||Rugby pitch|
The media rarely provide real-world examples of square metres and hectares, usually defaulting to imperial units.
|250 millilitres||Mug of tea|
|750 millilitres||Bottle of wine|
|9 litres||Household bucket|
Britons tend to use familiar measurements, typically those they have grown up with. The use of imperial units for personal weight and height is a typical example. But in addition to lack of familiarity, other causes of the UK’s measurement muddle may include inertia, habit, peer pressure, chauvinism (France invented it, but we do it better), hubris and wilful ignorance. Most countries around the world have made the change to a single, simple, logical and universal measurement system, in this process switching from the familiar to the unfamiliar. If we are as smart as we believe, then why can’t we? ‘Thinking metric’ will surely help.