By Helen on May 10, 2013 in Marking & Measuring Woodworking Techniques

**Seeing the difference. Metric vs Imperial**

Since learning metric measurements in school I’ve always been a user of the millimeter and never questioned its suitability. Richard was also taught metric first but as soon as he was out in to the practical world of work he adopted the use of imperial finding it much more intuitive. If he hadn’t put up an argument every time I presented a drawing in mm I think I would always have called the inch outdated and inferior. It just makes so much more sense to me to divide a measurement in to 10 equal parts; so much more simple to turn it in to a decimal or fraction. But sometimes we have to realize that our loyalty is simply a stubbornness through desire to stick with the familiar and since Richard can be so very persuasive I started to understand where he was coming from.

Despite the UK’s move to the metric system many moons ago it seems that there are great numbers still clinging on to their feet and inches so there has to be something that gives it an edge. Richard has often told me that it’s the centimetre that’s the problem and he’s not the only person I know who finds it a bit puzzling looking at cm’s when taking large measurements. After several years of becoming more familiar with imperial I think I’ve sussed why the cm is deemed by some as the measurement from Hell! It’s about the ratio between the various units in the system.

A centimetre of course is ten times larger than a millimetre and a metre is one hundred times larger than a centimetre. That’s a perfect relationship for simple mathematics but it isn’t very well balanced when visualising it on a tape measure. A centimetre divides up nicely in to small and accurate millimetres but compare a centimetre to a metre and it’s so small it gets lost. To aid this problem we tend to find that tape measures use a visual queue (a bold line or red number) at every ten centimetre interval and some goes as far as to miss any extra emphasis when we come to a metre instead continuing by calling them 100, 200, etc.

Dividing a metre in to ten like this is much more helpful when measuring long distances than seeing hundreds and hundreds of centimetres but this unit doesn’t really exist with its own name. The red ’20’ on the metric side of the tape in the photo is the location of 120cm but looking at it in isolation this isn’t immediately clear and to add to the confusion the same numbers ‘1- 9’ run continuously along the tape.

By contrast** imperial units come without the ease of having to only understand your ten times table**. A foot is made up of 12 inches and an inch becomes progressively smaller in divisions of 8, 16, 32 & even 64 should you need to go that small. This makes life difficult at the drawing board but just look at the photo to see how much clearer it makes things in the real world of full scale measurements. Long distances can be read simply with the bold and continuous markings of both inch and feet and if accuracy is required every 1/16″ is also noted. Finding 49″ inches or 4′ 1″ on that tape certainly jumps out much clearer and quicker than searching for 1.24m, 124cm or 1240mm.

The relationship between an inch and foot makes heaps more sense than that of a centimetre and metre and yet I would still never give up my metric system when making scale drawings. Perhaps then we will always continue to keep both versions alive as each definitely brings its own strengths for particular applications. It’s a prime example of when one thing is more suited to theory and another to practise. So…what do you use, and why?

**So what are your thoughts? ****Which system do you use?**

Let us know in the comments below.

I think it’s what your taught in your formative years. I suppose the metric system works well, but I grew up on inches and feet and fractions. Just makes sense to me. However, my wife, an ER Nurse uses metrics in her job all the time. I’m not saying I couldn’t adapt to the metric system. I just don’t want to.

I am still old school and use inches. Being a machinist and using a micrometer a lot I of course used tenths hundredths and thousands even ten thousands of an inch all the time. Much of the machine world has converted to the metric system now days but us old farts will die clinging to those inches and feet. Also most lumber is still manufactured in inches and feet for those building houses or whatever out of wood.

The biggest problem I have with Imperial is trying to calculate fractions.

Give me Metric any day.

I grew up with imperial. I do not understand metric, and probably never will.

It is confusing to us old farts when the temperature is in Celsius.

Fahrenheit rules in my house.

As a former trade teacher I found it much easier the teach the metric system, some students had trouble handling fractions

I grew up with the imperial system, and despite our ‘transfer’ to metric many metric sizes are near equivalents to the original sizes – copper tube is now 15mm and 22mm compared to half inch and three quarter because tubing is now measured as outer diameter instead of bore; sheet material is 2440mm x 1220mm instead of 8ft by 4ft: milk comes in a 2.27 litre container (4 pints).

Imperial beats Metric for subdivisions – metric being base 10 has less divisors than imperial, try dividing a metre into 3 equal parts compared to a yard. However, relationships between metric units are much simpler – for example 1 litre of water weighs 1kg and occupies 1000 cubic centimetres whereas a gallon of water weighs 10lbs and has a volume of about 277.42 cubic inches – I know which system I prefer!!

Sticking to one system presents no problem, and reading a measurement is only a case of using your eyes. The main problems occur when conversions are made with approximations.

Reading through your comments on subdivision of metres, the only real problem is because the UK only partly embraced the metric system. In Europe, a metre is divided into 10 equal parts called decimetres – yes a name does exist for those subdivisions. My 5 metre / 16ft measuring tape has red markings every 10cm and the numbers increase in multiples of 10 – so, for example 2.3 metres is marked as 230 in red. Thus you get multiples of 10 all the way – 10mm = 1cm, 10cm = 1dm, 10dm = 1m.

Confusingly, on the imperial side of the tape it still shows distances every 16 inches – originally the spacing for floor joists, which is now 400mm or 40cm or 4dm or 0.4m!!

Your comment regarding the relationship between a cm and a metre is a bit unfair – its like missing out feet and relating inches to yards.

Probably the biggest issue for all of us that grew up with the Imperial system is that this is what we learnt so any change will seem unfamiliar and less manageable. However, people that have only known the Metric system find the Imperial system to be so unnecessarily complex.