No, only in America is PCB design done in mils. Every other country uses mm. More information about the problems that has caused and continues to cause here. http://themetricmaven.com/?p=454

You just perfectly illustrated the problem with conversion strategies that involve keeping both units around. Even though you have the superior metric measurements available, you stick with what you're comfortable with, despite admitting that it also causes many problems with calculations.

If you actually did decide to switch to metric and not use imperial for any measurements, then you would very quickly get used to the mm-markings on a tape measure. It's also significantly easier if you get yourself a tape measure that is marked in mm, not cm. That is, one labelled 10, 20, 30, , 100, , and not 1, 2, 3, , 10,

Your work would speed up significantly because:

1. Using mm, all measurements and calculations would be done in whole numbers. You would never again have to do calculations with fractions, like 7 5/8.

2. Millimetre precision is sufficient for wood working, you very rarely need to use decmal fractions of a millimetre.

3. You would not need to memorise complicated fraction to decimal conversions, and vice versa.e.g. You wouldn't need to know that 0.4375 is 7/16ths or work out that 0.90625 is 29/32.

4. The kerf of metric circular saw blades are typically specified in mm to at most 1 decimal place. e.g. 1.5 or 2.0 mm. In imperial, that is usually specified as a decimal fraction of an inch to 3 decimal places. When you want to cut a piece of wood multiple times, accounting for this lost length is much easier than trying to do the same in inches. In metric, you can measure and mark multiple points to cut, precisely accounting for the kerf of the blade, and then cut all of them in one go. In inches. it's extremely difficult to measure, for example, 0.078" (a real value I just looked up). That particular blade is most likely exactly 2.0mm, as 2mm in inches is 0.0787 inches. Instead, you would have to cut, measure the next bit, cut again, and repeat.

There are probably more benefits too that I've missed. All of these benefits would more than make up for any lost time from trying to read a metric tape measure, which you would get used to very quickly, after which you would wonder why you didn't switch earlier.

In km, when you see a distance that is a multiple of 100, you can also very quickly determine how many hours it will take, at least on a highway, freeway or country road with limited traffic, when you assume an average speed of 100 km/h.

Also, it is much easier to instantly recognise a multiple of 100 than it is to recognise a multiple of 60, and also much easier to divide by 100 than by 60.

e.g. How many hours would it take you to drive each of these distances at 60 mph (assume distances stated in miles)?

a) 1020
b) 880
c) 900
d) 440
e) 1200

Now assume those are distances in km, repeat the same for driving at 100 km/h. The answers are much easier in km/h, because you simply divide by 100 and round to the nearest hour or half-hour.

Don't duel with dual. That was the motto adopted by the Australian building industry when they did the conversion, and for very good reason. Conversion strategies that involve using both units together consistently and continually fail to work. I challenge you to find a single, completely successful conversion program anywhere in the world that has succeeded by using and maintaining dual units. You won't find one.

The most successful conversion strategies are those that transitioned relatively quickly, where the old units were completely removed when the new units were put into effect. Pat Naughtin has written significantly about this effect, having been involved in the building industry and subsequently being involved with metrication processes around the world over the last 40 or so years. Read about it all on his website http://metricationmatters.com./

So, yes, there is a huge reason to not have a transition strategy that publishes both km and miles on speed and distance signs simultaneously. It won't work and will only serve to slow the transition process. If you simply specify a date, or at least a very short period of a few days, in which all signs will be changed over from miles to km, then the changeover will be much more successful. There are strategies to do this very quickly, if it is well planned. Australia did it, and the US could do it too.

The modern strategy would likely involve stick on replacement labels that go on to the existing signage, and the gradual replacement with more permanent fixtures as needed for general maintenance. Other strategies involve deploying new signage that is covered up until the changeover date, then subsequently covering and removing old signage. Australia did the latter over 40 years ago very successfully.

For weather, the scale is arbitrary and there is no technical benefit to having Fahrenheit over Celsius, or vice versa. People like myself who grew up with Celsius find Fahrenheight to be crazy and difficult to work with. People like yourself find the opposite.

However, having a temperature scale which, at one end, roughly approximates the core body temperature of a human, and at the other, being the coldest attainable temperature of ice water and salt mixture really has no benefit whatsoever. I've heard the argument about F being "more precise" than C because the magnitude of 1 F in nearly half that of 1 C. But it's bogus for several reasons.

1. It completely ignores how well the human body senses temperature.

We can roughly feel a change in temperature of about 1 C, and so for weather, having a scale more precise than that isn't really that useful. But even so, many modern digital thermostats support increments of 0.1 C anyway, which is more than enough precision.

2. It ignores how weather reports determine and report temperature

The temperature can change by several degrees between where you are and where the weather station recorded or estimated the temperature. Weather reports usually give relatively large temperature ranges for a given period, usually a day, or when stating only a single value, they state an approximate extreme for each region.

3. The "degrees of frost" measurement sometimes used in the US is based on the concept of degrees below freezing point of water, 32 F. That is a completely unnecessary concept when using Celsius because the freezing point is simply 0.

There are many applications in which the relationship to water is useful. Cooking, for one. Water is used a lot and having the temperature at which you cook things relate to water is extremely useful. If you want something cooked at 100C, then putting it in boiling water is fine. Other times, if you want something at, say 80 or 90 C, then you know that if it starts to boil, it's too hot. On the opposite end of the spectrum, you know you don't want things in your fridge to be frozen, so you want to ensure that it doesn't go below zero.

As a convenience, the temperature at which people can stand to touch relatively comfortably is around about half way up the scale, somewhere around 50C, give or take a few degrees. Hotter than that starts to get really uncomfortable and over 60C starts to burn quite quickly.

Another clear advantage is that if the entire world was using a single, common temperature scale for everyday use, regardless of which that was, it would mean far less need for conversion when communicating internationally. As an Australian, it is really annoying when searching for various things in English, only to find that so many sources are aimed at Americans with any stated temperatures published in Fahrenheit, which I then need to convert. Sometimes, it's not even clear what scale that's being used and I have to figure it out based on other information. Conversely, if an American finds some temperature they need to know published in Celsius, they would also likely want to convert it too, which annoying and time consuming.

As an example, looking up information about how to temper chocolate. A lot of the information is published with values in F. You need to know 3 separate temperatures for the process, and having to convert them to C and remember the new values is very time consuming and confusing.

Just to add to my comment, 100 cubic metres of sea water weighs about 103 tonnes, which is not far off from an approximation of 1 t/m^3.

In everyday applications, it does absolutely give a very useful approximation that is good enough. For cooking with ingredients that are specified in mL, it's often possible to simply put your mixing bowl on a scale and pour them in. The 1 g/mL approximation is close enough, and will probably still get you closer than if you tried to measure the ingredient volumetrically with typical kitchen jugs or measuring cups.

For large scale applications, such as building something that contains a lot of water (e.g. a large aquarium), determining the volume of the aquarium in cubic metres tells you how heavy all that water is going to be to a near enough approximation, which then lets you calculate how thick you need to make the glass viewing window to support it all, or how strong you need to make your building foundations. For such applications, an order of magnitude estimate in tonnes is enough it won't matter if you're out by even a few hundred kg, as you'd likely want to be able to support several tonnes over your estimate anyway.

No, 16 US fl oz is 473 mL, but 16 oz or 1 lbs is 453.5g. They are not the same.

16 UK fl oz of water, however, is equal to 16 oz at 62 deg F and 1 atm of pressure. This is based on the definition of the Imperial gallon as 10 lbs of water at that temperature and pressure, and there being 160 fluid ounces in an Imperial gallon, as opposed to the 128 fl oz in a US gallon.

Also, the Imperial and USC ounces are not different because the reference temperatures are different. They are different because the definitions of the gallon is different. The US gallon is exactly 231 cubic inches.

Easy unit conversions is not the only benefit of the metric system. The ability to work entirely, or almost entirely, with whole numbers and only a single unit for each measurement, regardless of your application, is another huge benefit. It makes calculations significantly easier than working multiple units and fractions.

In construction and most other engineering, working entirely with mm allows you to use whole numbers for everything, as you usually never want more than mm level precision for such projects. You can use a single unit for all measurements in a plan. For a house, everyone from the architect to the brick layer to the carpenter and carpet layer and whoever else do everything exclusively in mm, and rarely, if ever, use any decimal places for anything and absolutely never use fractions.

When working with feet and inches, you often have 2 separate units - feet and inches, sometimes with an added fraction - all mixed into a plan. Some people would work just with inches, such as those tradesman working on the small scale stuff, whereas the overall floor plan is done predominately in feet. It's all just a confusing mess.

Don't forget that the feet used in the construction of roads, where miles are relevant distances, are ever so slightly different from ordinary feet. Road construction in the US is done in chains of 100 US survey feet, which for long distances, are measured with GPS in metres before being converted for planning.

There are many advantages to having paper that is sized based on area, and with sides that have a clear relationship to each other. The exact lengths aren't that important for most tasks

One advantage of having the system set up with a sqrt(2) ratio is that folding a sheet of A4 in half makes it the size of A5, and this works for any size in the series. This is particularly useful for photocopying, where you can copy 2 A4 sheets, scaled down by 50% to fit 2 pages per sheet evenly.

The C sizes of the system are also useful. The exact dimensions and how they're calculated aren't important, but a C4 envelope will fit a flat A4 sheet, a C5 envelope will fit an A5 sheet, or folded A4 sheet, and the special C5/C6 envelope fits an A4 sheet folded into thirds.

The density of the paper is specified in g/m^2 (grams per square metre, or "gsm"), with the common density for standard office paper being 80 gsm. That means, 1 sheet of A0 paper would weigh 80g, and A4, being 1/16th of that weighs 5g. Conversely, 16 A4 sheets weighs 80 grams. A standard ream containing 500 sheets is 500*5g = 2.5kg. Now, you can easily calculate the mass of any number of sheets, which is very useful for shipping purposes. More imporantly, it also lets customers compare the density of different sized paper products. e.g. 80 gsm A4 paper has the same density as 80 gsm A5, so they can know what quality of paper they will be printing on.

Compare this with the US system, where paper mass is measured with the complicated basis weight system, in lbs/ream. But it doesn't represent the mass of the paper as sold to the customer. It represents it at some stage in the manufacturing process before the paper has been cut to size, and this weight can't be reliably compared among different sizes of paper. e.g. Letter size paper rated at 5 lb/ream is not necessarily going to be as dense as a US legal size paper rated at 5 lb/ream.

In reality, the US does have a dual system of measurement, and that is what's costing the US so much. The general population may think everything is in USC, but a lot of engineering is done in SI units, or in some cases, in a mixture of the two systems.

For example, PCB boards in the USA are designed in mils (1 mil = 0.001 inches), and yet many electronic components are sized in metric. This results in rounding errors and parts that don't quite fit and need a lot of manual corrections. More info here. http://themetricmaven.com/?p=454

Actually, there's also a third system in use too, but that's mostly hidden from the general population. Roads in the US are measured and constructed using Ramsden's chain, which is 100 US survey feet, where a survey foot is slightly different from a regular foot. Each foot is divided into decimal fractions. But then, for long distances, they actually measure it with GPS, which gives readings in metres that then need to be converted for entry into the design software. It gets even more complicated that that, and that's explained in more detail here. http://themetricmaven.com/?p=465

No, they don't use micrometres on a construction site. In Australia, it's all millimetres. The lengths they commonly use (e.g. 600mm between studs in the wall, 2400mm ceiling heights) are easily divisible by 2, 3, 4, or 6 when needed. Tape measures in Australia measure in mm, not cm, especially those used in construction. You are highly unlikely to find centimetres or micrometres anywhere on a construction site. Micrometres are used for much smaller scale engineering. The kind of thing you'd need a set of vernier callipers to measure.

Actually, you can eat gold.

http://en.wikipedia.org/wiki/Gold_leaf#Culinary_uses

In Australia, cans are 375 mL, and in Europe they are 330 mL.

1 mile is 1.609344 km. I suspect the GP confused the conversion of 8 feet to 2.4m with miles to km.