Our country seems like it will never officially convert to the metric system. This is despite the fact that a LOT of our industry has already converted and is happily operating on the metric system. Our industries found this was something they just had to do in order to keep up with the world where EVERY other industrial country was using the metric system. In order to actually use parts and materials from other countries, that were less expensive and sometimes better, they had to switch to the metric system.
If you are going to work on any piece of recent mechanical equipment you had better have your metric tools handy. Although the SAE tools that you have may be used in many cases, the fit won't be good. You just won't be able to get that 1/2 inch wrench to quite fit that 12 mm bolt.
No country has converted to metric easily. The process frequently had to be forced with the general population strongly opposed to the process. In the end everybody has benefited. There is nothing better than for everybody to be on the same page when it comes to measurement.
This won't be quite what you think - I'm talking about learning to 'speak' the language of metric. When you learn a second language - I mean REALLY learn it - you have to start THINKING in that language. No person who learns a second language and is fluent in that language can take the time to convert from the second language to their native language. You have to actually think in that second language to be fluent.
The same is true for the metric system. It's a foreign language to most of us in the United States because we were taught the SAE system in school. We STILL teach the SAE system in schools as the primary measurement system. Until that changes we will have to become bi-lingual (in measurement) to effectively interact with the rest of the world.
Learning how to convert from one system to the other is NOT the right way to accomplish this. It's the equivalent of someone learning German by using an English-German dictionary and converting every word from German to English. It just takes too long and is not that accurate.
So we have to learn a new way of measuring things and become comfortable in that system. We ONLY need to convert from one system to the other when there is no other choice. With any luck, this situation will be very rare.
There are several types of measurement that come into our lives:
This one is pretty easy. SAE measures length in inches, feet, yards, miles and a few other oddities. None of these has any seemingly sensible relationship to each other. In the metric system we have millimeters, centimeters, meters, kilometers and a few others at the extreme ends. ALL of these measurements are based in tens - 1000 millimeters = 100 centimeters = 1 meter. 1000 meters = 1 kilometer. There are no odd multiples to keep track of. The metric system is EASY to learn the relationships between general sizes.
But ... how do I know how long a foot is in metric? DON'T BOTHER! It's not that important to know the relationships between the systems. You just have to know the relations within the metric system. Getting a feel for metric measurements will lead you to a better understanding of the entire system.
For example, how big is a centimeter? No, DON'T CONVERT IT! If you must get a general grasp, think of 2 inches being about 5 centimeters. Precision of conversion is not necessary to get a 'feel' for the size of something. By the way, 2 inches is exactly 5.08 centimeters. Is that last 0.08 centimeters important to get a 'feel' for the size. Certainly not.
A meter is a bit longer than a yard. This will give you a 'feel' for the size of a meter. 5 kilometers is a bit over 3 miles. These should give you a 'feel' for the length of things.
Square feet, square yards, acres, etc. How many square feet in an acre? I don't know and I don't really care. Square centimeter, square meter, square kilometer - all are easy to figure their relationships. 10,000 square centimeters in a square meter. 1,000,000 (1000 x 1000) square meters in a square kilometer. 6 square centimeters is about a square inch. A square meter is a bit bigger than a square yard. You just need a bit of a reference so when someone says their back yard is 500 square meters they mean a bit over 500 square yards.
Volume is a measurement we use a lot more than area. Mostly we think in gallons and quarts. Quarts are a bit smaller than a liter. A gallon is a bit less than 4 liters. It's not uncommon to buy 1/2 liter bottles of soft drinks. It's a nice size - a bit over 16 ounces. And who can forget the 2 liter bottles that came along quite some time ago.
Back when gasoline prices were creaping up on the $1 per gallon price and gas pumps ONLY read up to 99.9 cents there was serious consideration to changing all of the gas pumps to operate on liters. That would have eliminated the need to convert all of those gas pumps to have a dollar digit. It didn't happen - we missed our chance to move at least something to the metric system.
Temperature is a different animal. There is no conversion within a system and Fahrenheit uses only degrees. But the degrees for the metric system (Centigrade) are a different size and there is the problem. I struggled with this changeover myself and finally used the following 'chart', with appropriate clothing specifications, to keep things straight:
| Centigrade | Fahrenheit | Notes |
|---|---|---|
| -40 | -40 | Equal values - Stay inside where it's warm. |
| -20 | -4 | Cold! - heaver winter gear if you must, better to stay inside. |
| -10 | 14 | Cold - heaver winter coat, hat, scarf, etc. |
| 0 | 32 | Water Freezes - Cold! Heavy winter coat. |
| 5 | 41 | Still cold - moderate winter coat. |
| 10 | 50 | Cool - light jacket. |
| 15 | 59 | Brisk - light jacket, sweater. |
| 20 | 68 | Getting pleasant - flanel shirt or even a t-shirt if it"s sunny. |
| 25 | 77 | Warm - short sleeves. |
| 30 | 86 | Getting hot - shorts. |
| 35 | 95 | HOT! Stay inside with the air conditioning. |
| 37 | 98.6 | Normal body temperature. |
| 100 | 212 | Water boils. |
| 237 | 459 | Paper burns. |
| 1538 | 2800 | Iron Melts. |
You don't really need to know every temperature conversion, just a few so you can get a feel for how to dress. I set my thermostat to 24 degrees (75 fahrenheit) in the summer for the air conditioning.
This is an odd one. We use weight (pounds and ounces) in SAE and mass (grams and kilograms) in metric. There is a difference between the two concepts but ON EARTH both have meaning. Without gravity, weight is always ZERO. Gravity is required for weight to have a meaning. Mass exists whether there is gravity or not.
Since we ARE on the earth and in it's gravity field we'll forget the differences in this discussion.
Pounds to kilograms is a pretty easy conversion - 2.2 pounds for one kilogram. That means if you weigh 220 pounds you would mass 100 kilograms. One ounce (normal, not the kind used for precious metals and such) is about 28 grams. A simple and readily available measure for grams is our own nickel coin - it masses 5 grams exactly. This is not something new, it's always been this value since it's introduction in the late 1800s.
I think we can expect to see prepackaged foods moving to metric measurements. Most foods have been marked for both (1 pound is 454 grams) for some time now. As the sources for these commodities becomes more global I think we will see weight/mass favoring the metric (1.1 pound or 1/2 kilogram). That's my opinion and I'm sticking with it.
This is one I haven't really dealt with yet. I don't deal with pressure much myself other than atmospheric pressure. For the record, the average sea level pressure is 1013.25 millibar, 101.325 kiloPascals, 29.921 inches of Mercury, or 760.00 mm of Mercury. For atmospheric pressure it's all relative - is the pressure high or low. The measured value is generally used by meterologists and airline pilots. They both tend to use either milibars or inches of Mercury.
I know there are other pressure measurements but I just don't run into them so I have to claim no knowledge in this area.
Here is something that is generally important to us all. If you drive then you know about miles per hour. The metric way is kilometers per hour. Here's a few common values (these are approximate): 25 MPH = 40 KPH, 35 MPH = 55+ KPH, 45 MPH = 72 KPH, 55 MPH = 88 KPH, 65 MPH = 105 KPH, 75 MPH = 120 KPH, 250 Knots (airplane max speed up to 10,000 feet) = 463 KPH.
Although I have been converting every measuring device (thermostat, weather app, etc.) I can to the metric system my car just won't do it without swapping out the electronics module. A 2005 Honda sold in the US was in miles ONLY. I'm sure the newer ones aren't that restrictive.
Some good news for you - THERE IS NO SPECIAL METRIC TIME SYSTEM! For some reason time is time everywhere. You just have to deal with time zones.
As a friend of mine often says: The same way you eat an elephant - one bite at a time. Don't try to do it all at once. I started 5+ years ago when I realized that when I was confronted by a metric length measurement I just naturally had a feel for it. I also realized that I had the quarts/liters thing down pretty well too. Then came weight: pounds/kilograms. About a year ago I worked into temperature. As you can see, it's been a slow process and is still ongoing. I relish the opportunities to tell someone what the high temperature for today will be. If they ask me what this is in normal degrees I just repeat it. If they ask what it is in Fahrenheit then I put on that look that I'm calculating and give them an approximation.
I hope you've learned something from all of this. I hope you have at least decided to consider learning this new 'language'. I know I've been enjoying the challenge of learning. No excuses - I'm 65+ and if I can do it anybody can!