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Everyday usage of metric

In normal usage in the UK metric appears quite often and in many places.



In the UK, paper sizes have been metric for many years, using the international A series standard. Most office workers are familiar with A4, which is used on laser printers, inkjet printers, photocopiers, and for letterheaded stationery.

A4 paperThe A series of paper is based on the base size of A0 having an area of 1 square metre. All A-sized pages have a ratio of long side to short side equal to the square root of 2, which is approximately 1.414.

This means that when you halve the size of a sheet of A4 (along the longest side), the resulting two smaller pages will have the exact same ratio of long side to short side of 1.414. The new page sizes add 1 to the number as they are halved in size, and if you halve the size, then 1 is added to the size, e.g. half of A4 is A5, and if you double the size then add 1 to the size, e.g. A3 is double the size of A4.

A4 sheets are 297 by 210 mm in size, A3 are double in size at 297 × 420 mm. A5 is 148 × 210 mm.

The diagram below shows the relationship between A4 and A3. Note that an A3 sheet has double the area of an A4 sheet of paper, and that 2 A4 sheets fit exactly into the size of an A3 sheet.

Two A4 sheets put together make one A3 sheet


A0 paper size has an area of 1 m² (one square metre), it follows then that A1 size must be half a square metre in area, A2 is one quarter of 1 m², A3 is one eighth, and A4 is one sixteenth.

The weight of paper is expressed in grams per square metre, written properly as g/m², however it sometimes is written as gsm.

If the paper you are using has a weight of 80 g/m², then if you have enough paper to cover an area of one square metre, such as 16 sheets of A4, those sheets will weight 80 grams.

DL envelopes 110 by 220 mm in sizeThis is helpful in posting letters, for example, as if the paper has a weight of 80 g/m², then each individual sheet of A4 is 80 grams divided by 16 sheets, which is 5 grams for each sheet of A4 paper.

Standard first class postage in the UK covers weight of the letter/envelope up to 60 grams, so it should be no more than this to use a standard first class stamp. If we say that the envelope weighs 10 grams, then you can put 10 sheets of A4 inside (50 grams). Very handy to know. Read more about paper sizes here. A4 letters can be folded into thirds to fit neatly inside the standard DL-sized envelope, which is 110 × 220 mm.


first class stamp for letters up to 60 gramsThe Royal Mail has been metric for a long time, giving prices for set intervals of weights in grams. For example, a first class letter in the UK weighing up to 60 grams, will cost the standard rate for first class post, but if it weighs over 60 grams up to 100g, then the cost will be more, and then each 50g increase will increase the price to the next level. See their guidance notes on size and weight, all of which are in metric.


Doctor and Medical

Doctor measures height of a boy, in centimetresIf you go the Doctor and have your weight or height measured, it will usually be in metric. Although some medical places might quote you the sizes in non-metric units, some will quote in metric, and certainly all data is recorded in metric in the NHS.

It can be very helpful to know your height and weight in metric, as you can use these figures to easily calculate your Body Mass Index (BMI). BMI is calculated using the formula BMI = weight divided by height squared, i.e. kilograms divided by metres squared, e.g. 72 kg/(1.72 m × 1.72 m) = 24.3. More information can be found on our page on weight and mass.

Medicines are labelled with values in milligrams and micrograms. Remember that milli means thousandth, and micro means millionth.

When you visit the gym, they are likely to measure skin folds in millimetres and to calculate your body mass index using your mass in kilograms and your height in metres.



picture of tomatoesWhen you go to the supermarket, you will probably find all weights, volumes, etc. in metric units, e.g. can of beans with 400 g on the side, bag of pasta with 500 g on the packet, bag of frozen chips with 1.8 kg on the packet, bottle of water labelled as 2 litres. When you see the prices for frozen vegetables and see the prices for fresh vegetables, both priced per kilogram, you can easily compare prices, both between products and between supermarkets. Supermarkets also give comparative prices, e.g. price in pence per 100 grams (see image below).

Most household products you buy are measured in metric, such as a tube of toothpaste having a volume of 100 millilitres, shampoo labelled as 250 ml, and various other bathroom products, in ml or if measured by weight, then in grams. 39.6p per 100g

Despite not always having metric labels on, in the UK (and most countries in the world) all clothes have been designed and manufactured using metric measures.

Can of beer with volume of 440 millilitresAll soft drinks and prepacked alcholic drinks are in metric sizes today. Wine comes in bottles sized at 750 ml, often written as 75 cl (cl = centilitres, and 10 ml = 1 cl). Beer in cans and bottles might be 440 ml, 500 ml, 660 ml or other multiples of millilitres.

Soft drinks in cans in the UK are often sold in a size of 330 ml, which is about one third of a litre. Mineral water is sold in bottles of 250 ml, 500 ml, 1 litre, 2 litres, and other metric quantities.

The food/drinks you buy will often have nutritional information on the packaging, such as how much energy, fat, protein, sodium, etc., per 100 g or per 100 ml of the product. Whether the energy value is in joules or calories, both are metric units, although joules are a better way of measuring energy.




100 watt light bulbThis has always been metric. The unit of power, the watt, is named after British scientist James Watt, and all electricity pricing is in pence per kilowatt hour.

This means that for every appliance that uses 1 kilowatt of power for a period of 1 hour, that price in pence is what it costs to run that appliance, e.g. if the cost is 10 pence per kWh, and the appliance uses 1 kW and is used for 1 hour, then the cost is 10 pence. If it uses 2 kW, then the price doubles to 20 pence in 1 hour. If it uses 100 watts, which is one tenth of 1 kilowatt, then it uses 1 penny per hour (such as a light bulb).

Or if you have 5 light bulbs at 100 watts each, running for only 3 hours each day, for a whole year, then the cost per year would be: 10 pence × 5 bulbs × 0.1 kW × 3 hours × 365 days = £54.75.

Other metric units of electricity include volts, amps, ohms and farads.



computers are metric throughoutAll computers use electricity, and are made to metric standards. Don't be fooled by things like the, so-called, 3½" floppy or 17-inch screens; these are examples of hidden metric. According to international standard (ISO/IEC 9529-1) floppies are 90 mm x 94 mm x 3.3 mm, with a mass of 24 g, and the magnetic media inside is 86 mm — not a 3½ anywhere!

All other computer components come with metric specifications. In addition to the clock speed of the computer, in MegaHertz, and the size of the memory, in MegaBytes and GigaBytes, all the fasteners and other parts of your computer, all the way down to the substrate to make the computer chips is metric.



Gas bills are also now produced with costs in pence per kWh, which makes it very easy now to compare gas costs with electricity costs.



PetrolAll cars in the world (including all those in the USA) have been fully metric since the development of interchangeable parts for the "world car concept" in the early 1970s. Every modern family car has (about) 10 000 separate parts, each of which requires (say) 10 measurements. All cars have been measured some 100 000 times — using metric measures — often to the nearest 100 micrometres (1 micrometre is a millionth of a metre, it is also a thousandth of a millimetre, and is sometimes referred to as a micron, although micrometre is the preferred unit name).

Petrol and diesel fuel has been sold in litres for many years, making price comparisons very easy over time, and in comparison with other countries. In October 2004, when petrol cost around 80 pence per litre in the UK, it was costing only 30 pence per litre in the Middle-eastern country of Jordan.

Engine sizes have always been measured in cubic centimetres and litres. A typical engine size for a small car would be 1000 cc, which is also 1 litre, for a mid-size car around 1400 cc, which is 1.4 L, and for a larger car it might be 2000 cc, which is 2 litres. This capacity is not the actual size of the engine, but rather it refers to the the displacement or swept volume by the pistons of the engine (the total volume of air/fuel mixture an engine can draw in during one complete engine cycle, as the pistons are moved from top dead centre to bottom dead centre).



In industry and manufacturing products are produced in metric. The military have been using metric for years. Importing and exporting is all in metric too.


cameraIf you use a still camera or video equipment these, too, have been totally metric products since the Kodak company, in the USA, made their decision to use B&W 16 mm film for amateurs in 1910 and their 16 mm colour movie film in 1929. Most cameras today take 35 mm film, and the digital ones use MegaBytes. Printed photos may be specified in a shop in non-metric units, but really they are usually 100 by 150 mm for the standard size.


CDs and DVDs are 12 cm in diameterIn the home entertainment world, CDs and DVDs have always been 120 mm in diameter, and the old-fashioned vinyl records have always been 175 mm, 250 mm or 300 mm since the 1930s (the inch sizes are just an inaccurate approximation). By the way, in 1959 the inch was redefined as 25.4 mm exactly.






20 kg of luggageWhen you go on a flight, there will normally be a baggage allowance specified in kilograms, usually 20 kg per passenger. Some airlines/flights may have a higher limit of 30 kg.

During the flight on some aircraft, there will be a TV screen showing flight data, which may well show you the distance from your starting point in kilometres, distance to destination in kilometres, altitude in metres (e.g. 10900 m), temperature outside in degrees Celsius (e.g. -55°C — it gets very cold outside at high altitudes), and groundspeed in kilometres per hour (this is the equivalent speed of the aircraft if it were at ground level, as the distance from your starting place to destination is measured at ground level).

Also, if you are flying to any country other than the USA, when you get there you will find that everything is in metric. Virtually all countries (outside of the UK) have speed limit signs on roads in km/h. Even the USA has some speed limits in km/h, although the majority are still in miles per hour. Ireland changed all its speed limit signs to km/h in January 2005, as well as road distance signs to kilometres. The USA has a few road distance signs in km, but most in miles. All other countries usually have road signs in km. Most countries follow the international standard designs for road signs (not the USA though) so you will find that most road signs look familiar, although the numbers will probably mean something different to what they mean in the UK, e.g. a red circle with black number 50 inside it will mean 50 km/h not 50 mph.


map showing temperatures in the UK when it is coldWeather forecasting the UK is typically done using the metric units of temperature, degrees Celsius. Maps on TV forecasts showing temperatures in Celsius only. Newspapers usually give temperatures in degrees Celsius too, and whatever forecast is given, get used to how it feels outside, such as when the forecast is for 11 degrees, then it will feel cold outside, or if the forecast is for 25 degrees then it will feel hot, and you can get used to the different numbers in Celsius and relate them to how it feels outside.


metric uses the second as its base unit of timeThe second is the metric unit of time. All other units, like minutes and hours, are derived units and are found in metric measurements such as kilometres per hour and kilowatt hours. As the whole world uses the same system of time measurement, there is no need to change to a different system.




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Ruler in centimetres, because metric is very useful