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Metric conversion

Metric conversion is one of the ways that you can upgrade to the modern metric system eventually.

We say eventually because the metric conversion process is slow painfully slow.

Many people who have chosen the metric conversion path have found through bitter experience that upgrading to the metric system using metric conversion can be really slow, very difficult, and extremely costly. Whether your metric conversion to the modern metric system is aimed at yourself, your work group, your company, or your nation you will also find that metric conversion is one of the slowest possible paths.

The great American journalist, H. L. Mencken, could have been talking about metric conversion when he wrote:

... for every complex problem there is a solution that is clear, simple and wrong.

To understand why metric conversion is so difficult and so slow, you need to know that metric conversion actually involves three quite separate and distinct learning pathways. One of these is quite simple but the other two can be enormously complicated and correspondingly slow.

When you choose a metric conversion path to take you and your companions toward full use of the metric system you are unavoidably making these three learning decisions. You and all of your companions will learn:

1 about the metric system this is quick and easy.

2 lots about old pre-metric measures more than you have ever needed to know before.

3 a whole new world of conversion factors and on how to use them.

Note that learning about items 2 and 3 will have no useful purpose in your life in the long run. You could think of them as learning truly pointless metric conversion information and developing quite irrelevant metric conversionskills.

To compare these three different learning paths we might consider the measurements of land for housing and for farming that were formerly measured in such measures as feet and furlongs, square feet and acres.

1 Learn about the metric system

A square 1 metre long and 1 metre wide has an area of 1 square metre.

A square 100 metres long and 100 metres wide has an area of 1 hectare. There are 10 000 square metres in 1 hectare.

That's it all you will ever need to know about area in the metric system for housing and farming. (You could learn about square centimetres, square decimetres, and about ares and hectares but remember the KISS principle Keep It Simply Structured and only choose the minimum amount of metric information that you need to learn).

2 Learn about old pre-metric measures

Old pre-metric measuring might involve feet, yards, rods, poles, perches, furlongs, chains, or miles together with square feet, square yards, square rods (also called roods), square poles, square perches, square furlongs, square chains, acres, or square miles. However, although these are all valid measurements, to reduce the complexity we will only refer here to the two different kinds of feet that are used in the USA.

You might ask if this is relevant in the 21st century and the answer is yes. If you buy land in South Carolina it will be measured using a foot that might be called an International foot, a statute foot, or an Imperial foot. If you buy land in North Carolina it will be measured using a different foot called the survey foot.

If you buy land in Oregon, you could be using either statute or survey feet, as both are legal. Mostly land will be measured using the International foot but there is also a chance that it will be measured using the survey foot; Oregon defines the US Survey foot as 1200/3937 meters exactly and the (International) foot as 0.3048 meters exactly; these are slightly different lengths. Obviously, if you buy land by the square foot it is best to know which foot is being used. You will have to check the defined length of the foot for each state. If you are referring to old title deeds you also need to know how the length of the foot was defined in the past as the length of the foot has changed several times from 1795 till now.

For buying agricultural land, you will also need to know about acres. You can picture the traditional acre (defined this way since about 1834) as a strip of land 1 chain wide by 10 chains long. This is 4 rods wide by 40 rods long; 22 yards long by 220 yards wide; or 66 feet long by 660 feet long. As we have decided to only use feet, we can calculate that 1 acre is equal to 43 560 square feet (66 feet x 660 feet) but of course acres vary in size according to where it is because, as you now know, feet vary in length; there are just as many different chains as there are different feet!

Just because there was an international agreement about the lengths of the inch and the foot in 1959 does not mean that there are not forces still wanting to change the length of a foot. For example, the UK Royal Navy uses a 'data mile' of 6,000 feet where each foot is about 223.24 millimetres. And the USA Navy has defined a mile of 6 000 feet for ballistic and cruise missiles.

3 Learn about conversion factors

When you are choosing conversion factors for land sales you need to know that:

  • The length of the metre is exactly and precisely the same length as it was in 1795 it has never changed.
  • The definitions of the lengths of feet, yards, rods, poles, perches, furlongs, chains, or miles together with square feet, square yards, square rods (also called roods), square poles, square perches, square furlongs, square chains, and square miles have changed every few years roughly every generation since the late 1700s. A current definition is based on the international inch of exactly 25.4 millimetres. This gives an international foot of exactly 304.8 millimetres. However, be aware that just prior to 1959, the inch and the foot had different lengths in Canada, in the UK (2 values), in the USA (2 values), and in South Africa.
  • For buying housing or agricultural land, you need at least these conversion factors:

3 feet to 1 yard
5 1/2 yards to 1 rod
4 rods to 1 chain
22 yards to 1 chain
10 chains to 1 furlong
You need to know all these words because old pre-metric land deeds are drawn and written using various, apparently random, combinations of some, or all, of these. Some of these differences still persist. For example, a survey foot is defined (in Oregon) as 1200/3937 meters exactly and the International, statute, or Imperial foot as 0.3048 exactly. This means that the size of acres varies within Oregon as it also varies from state to state. The South Carolina acre is 4046.86 square metres and the North Carolina acre is 4046.87 square metres. It doesn't vary much but people worry when thousands of acres are involved.

If you are looking at an old map of land you wish to buy, you will probably need to know how long each foot is, and how long the foot was when the map was made, and by whom it was made. As an example, consider the city of Melbourne in Australia, which is famous in town planning circles for its regular grid lines that are 6 080 feet (using British Imperial feet of the year 1837) from north to south and 12 160 feet from west to east. Although this area is sometimes called the 'golden mile', few Melburnians realise that the miles are nautical miles because the surveyor, Robert Hoddle, was a Naval Officer. In the 21st century land sales in Melbourne still have to accommodate 'Hoddle feet' whenever land is bought or sold.

If you ever decide to take the 'metric conversion' path to completing your upgrade to the metric system keep in mind that you will need to confront all three of the above issues. Be aware that others have taken this path and they have spent many, many years trying to complete their metrication upgrade this way. Typically, you can expect to take 100 years or more on a 'metric conversion' program and you can expect bitter fights about which definition you should choose from the many old pre-metric definitions available and about which is the 'correct' conversion factor to use.

It is best to simply choose step 1 from the three learning paths and then to stop there:

  • learn as little as you need to know about the metric system for your current task;
  • remember the KISS principle Keep It Simply Structured.
  • only use metric system units, and;
  • don't ever convert anything!

Another problem with metric conversion is that most people use metric conversion factors to change from metric units back to the old pre-metric measures every time that they see a metric unit.

When someone says: 'I am 1.7 metres tall', they ask, 'What's that in feet and inches?'

When someone says, 'The baby was 3600 grams', they ask, 'What's that in pounds and ounces?'

When you hear these responses, you might think that here are people doing some metric conversions, but the truth is that they are doing Imperial comversions (or English conversions in the USA) when they convert from the modern metric units, of metres and grams in the above examples, to one-or-other of the old pre-metric measures. Metric conversion is almost always a method to delay upgrading to the metric system directly, quickly, and cheaply. Metric conversion is your second choice below:

I suspect that most people who choose metric conversion simply don't know about the best possible path to the metric system that is called direct metrication.

Another approach to metric conversion is to do all of your designs, manufacturing, and product testing in metric units and then to dumb these down to old pre-metric units for the public. This is called 'hidden metric' and it is the approach taken by the automotive and computer industries. 'Hidden metric' is your third choice below.

Essentially, there are four approaches that you can take when you decide upgrade to the metric system.

Approach 1

'direct metrication'

Plan, design, and build in metric units, and then communicate with your customers and the public in metric units.

This path leads to smooth, economical, and quick metrication.

Companies that have used this approach have almost always found that their metrication upgrade has more than repaid the costs that they thought that metric conversion would bring.

At its best, this approach can take a company less than a year to complete their metrication process. Typically, they can also expect to save around 10 % of their turnover by increasing efficiency and decreasing errors and inventory.

For a discussion on this in the USA go to: /articles.html to download the article, 'Costs of non-metrication'.

Approach 2

'Do nothing while you pretend to be up-to-date'

Design and manufacture in old measures and then use metric conversions (almost always soft conversions that are too precise) to communicate with the public.

This is the heart of where metric conversion most often happens in companies when they decide to give the illusion that they are about to 'Go metric' while all the time they have no intention of doing so.

As you can see, these designers and manufacturers have no intention of converting to metric anytime soon they just want to give the illusion that they are converting. Somewhere on the staff of these companies is one, or more likely, several people who are the metric converters with the responsibility for doing the metric conversion calculations.

This approach has meant that many customers of these companies then need to have metric conversion calculators, metric conversion charts, or metric conversion tables to convert the bogus metric measures back to the old pre-metric measures that were used for the initial measurements. This is why most metric conversion resources on the internet are dedicated to converting from the metric system back to old pre-metric measures.

This is a extremely costly approach that will probably take about 1000 years. The time of 1000 years is based on the experience of shoe makers who took this approach to shoe sizes in about the year 1300 and most of us are still using shoe size numbers 700 years later and there is little prospect of change anytime soon.

Approach 3

'Pretend to do nothing' or 'Hidden metric'

Do all design, processing, and manufacture in metric units and then communicate with the public in old pre-metric measures.

This is the approach taken by a great deal of industry in the USA. It is hard to know how common this practice is, but it is probably in use by more than 70 % of all industry in the USA.

Think of a car made in the USA. This will be made with all of its 10 000 parts designed and built using metric units; these are then put together using metric bolts, metric screws, and metric glues. Finally the speedometer is labelled with mph for miles per hour and the tyres are labelled psi for pounds per square inch. Most drivers then firmly believe that they are driving an all 'English' car and all is for the best in an all 'English' world.

As a second example, look at the computer in front of you. The computer chips that control it are designed and built using nanometres, the circuit boards and the case are designed and built using millimetres, and finally, the screen is designed and built using millimetres then it is labelled in inches. Most computer users are then quite unaware that they are sitting in front of and using an all-metric computer.

This approach took less than 10 years from the mid-1970s when car and computer engineers realised how easy metrication was and how much money they could save by using metric conversion as a opportunity to reconsider many of their measurement processes. However, the public was not prepared to accept the truth of this metrication so the engineers used inches, mph, and psi to hide their metric conversions and to make their customers feel a little better.

Hidden metric is everywhere. The food, electrical, medical, pharmaceutical, and scientific industries are all close to 100 % metric.

Approach 4

'Do nothing' or 'Ignore it, and it will go away'

Keep all design and manufacture in old measures and communicate with the public in old measures.

With this approach you don't need to do any metric conversions at all. Obviously, this approach will take you a very long time to complete your metric conversion. Plan on your converting taken a lot more than 1000 years.

Whatever your situation, it is now probably impossible to 'Do nothing' or 'Ignore it, and it will go away' in the early 21st century the metric system is already everywhere in our lives for a discussion on this in the USA go to: /articles.html to download the article, 'Don't use metric'.

For a more details on the four approaches to the metric system go to: /articles.html and download the article, 'Approaches to metric'.

Don't forget that metrication need only be done once. After that you simply continue to use metric values and metric units. There should never be a need to redo any metric conversion calculations. Metrication is for ever!

To explore direct metrication further start at / or go to /newsletter.html to sign up for the free monthly Metrication matters newsletter.

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Pat Naughtin
Metrication Matters
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