# Gasoline efficiency

Here’s a question I’ve always wondered about: if you live (and are driving) in a country that uses kilometers instead
of miles, how do you rate fuel efficiency? You clearly can’t talk about “mileage,” because those units aren’t used. So what is it? “Kilometer-age” is awkward, “kilometers per”…not “gallons,” so “liters?” Questions, questions. Does anyone have an answer?

Most countries rate liters per 100 kilometers (as in 3.6l/100km), IMHO a much better system than MPG, I would rather see ratings of x gal. per 100 miles here.

If you know your kilometers/liter consumption, and you know how many miles in a kilometer, and you know how many liters in a gallon, you can easily get miles/gallon.

Canada’s tough…They sell gas by the “Imperial Gallon” which I think is 4 liters…

In Mexico, the exchange rate is 11.85 Peso = \$1 U.S. dollar. Gas costs 9.08 peso per liter. How much does Mexican gas cost in dollars per gallon?

It has been many years since I was in school and was taught about the metric system, the English system and the US system.

Over the years there have been a few attempts to change to the far more logical metric system, but in the US people just will not accept a system where water boils at 100º and freezes at 0º They seem to think that 32º and 212º is somehow better. or that someone will rip them off if they change.

``Ignorance is costly, but we just don't seem to be able to correct it.``

I thought the reason was primarily miles. Businesses had all their transportation costs figured out, all the signs on every roadway, your average person not being able to understand the difference, etc. Well, that’s what I heard anyway. Think I lived in Europe at the time. I don’t remember ever seeing a single sign when I was “home” that had KM or even both on it. Putting both on all new signs would be the first step, IMHO.

chaissos wrote:
I don’t remember ever seeing a single sign when I was “home” that had KM or even both on it.

There are a few signs with kilometers in upstate New York near Quebec.

“Over the years there have been a few attempts to change to the far more logical metric system, but in the US people just will not accept a system where water boils at 100º and freezes at 0º They seem to think that 32º and 212º is somehow better. or that someone will rip them off if they change.”

Why is it important for water to boil at 100 and freeze at zero? I kind of like a temperature scale where nearly all the earth’s weather happens between 0 and 100 degrees, in fact, the Farenheit scale is a very logical scale for meteorology because most of the earth’s weather falls between 0 and 100 degrees F.
Furthermore, basing a temperature scale on the freezing and boiling points of water results in a calorie of heat being 4.18 joules of energy. If they wanted to keep the theme of deriving all measurements from the basic units of kilograms, meters, and seconds, they would have developed a temperature scale where a joule of energy raised the temperature of a gram of water exactly one degree.

I think that measuring efficiency by fuel units per distance instead of distance per fuel unit makes sense. It makes it much easier to average the fuel consumption. In fact, we should have measured speed in seconds per mile instead of miles per hour. This makes ETA and average speed calculations a lot simpler.

If you know MPG you can easily change it to gallons/x miles. Does it really matter?

Stick with one system. There is no need for conversion. It’s just much easier to either stick with SAE or Metric. Many many years ago one of my college physics classes this fellow student was having the hardest time doing some of the simplest problems. What his problem was…if the problem was in Metric…he would first convert everything to SAE then do the problem and then convert back to Metric.o SAE… He couldn’t believe how easy it was to just leave the problem in Metric and do the math…Metric system is a LOT easier to do math problems in since everything is in factors of 10.

437 km divded by 64 liters (for example) is not any easier than 437 miles divided by 16 gallons, sorry Mike.

It really doesn’t matter. However you measure it, the car will use what it will use. Any system that designates volume per distance traveled is fine as long as you understand the system.

Joseph, while I agree that the metric system is more logical, the barrier to conversion is the enormous amounts of money it would cost to convert the machinery, tooling, design documentation, manufacturing documentation, and standards in the manufacturing industry. And even then, if you were making replacement hardware for aging aircraft like, say, a B-52 or a KC-135, you’d need to convert back to inches to do so. You’d also have to convert all the tolerances. There are literally millions upon millions of design and manufacturing documents still in use that are in inches. And there are billions if not trillions of machines, tooling, and fixtures still in use that are in inches.

That would take into account the weight of the vehicle and give a number more indicative of true efficiency.

If they wanted to keep the theme of deriving all measurements from the basic units of kilograms, meters, and seconds, they would have developed a temperature scale where a joule of energy raised the temperature of a gram of water exactly one degree.

Uh, you mean a “calorie”? (Note: not a “Calorie”…that’s 1,000X bigger.)

@BLE: “Furthermore, basing a temperature scale on the freezing and boiling points of water results in a calorie of heat being 4.18 joules of energy. If they wanted to keep the theme of deriving all measurements from the basic units of kilograms, meters, and seconds, they would have developed a temperature scale where a joule of energy raised the temperature of a gram of water exactly one degree.

The calorie isn’t part of the SI system. Neither is water, although it is used, just like cesium is. Measuring calories by raising the temperature of water is relatively inexact. The joule has a more generic and precise. definition:

It is equal to the energy expended (or work done) in applying a force of one newton through a distance of one metre (1 newton metre or N·m), or in passing an electric current of one ampere through a resistance of one ohm for one second.

One advantage of the Fahrenheit scale is that it uses smaller units, but that’s just my opinion. Seems to me that in an area where distances are measured in miles and liquids are measured in gallons, MPG just makes sense, but as other people mentioned the conversion is trivial.

The boiling point of water is also relatively inexact. What if you live in Denver, CO or Taos, NM? What if there is a storm approaching and the barometric pressure is low?
Furthermore, I have never needed a thermometer to tell if water is frozen or if it is boiling.

One reason we have resisted converting to metric units for everything is because we are accustomed to measuring things with the older units and they are are points of reference. There are some units that are only used to measure certain commodities and there is no need to convert them, for example, carats for diamonds, barrels for crude oil, grains for gunpowder, cords for firewood, light years for astonomical distances.
Would the game of football be a better sport or easier to understand if you had to advance the ball 8.128 meters for a first down?
Miles are used to measure driving distances and only driving distances so the fact that a mile is 5280 ft is of no consequence, unless we start stating the distance for a first down in football in miles instead of yards. However when we drive to a distant city, miles is our reference point and if you give us kilometers, most of us would mentally convert it into miles in order to have an idea of how far it is. Nothing wrong with kilometers if that is you are accustomed to.
There are some things that I am accustomed to measuring in metric units, motorcycle engine displacement for example. Tell my you have a 750cc motorcycle and I pretty much know what you have and how it compares to motorcycles I have owned or ridden. Tell my you have a 45 cubic inch motorcycle and I find it necessary to mentally convert that to 750cc in order to compare it to other motorcycles I am familiar with.
The opposite is true for model airplane engines, tell me you have a 6.5 cc model airplane engine and I find it necessary to mentally convert that into .40 cubic inches to get an idea of its size compared to other model airplane engines I have had experience with.

It’s not that Americans are anti-metric, it’s just that many of our points of reference are in English units and if you tell me that your car uses 8 liters of fuel per 100 km, I have no idea if that is good gas mileage or mediocre gas mileage without converting it into mpg first.

"The boiling point of water is also relatively inexact."
True, but… SI uses water of a certain level of purity to a certain degree of accuracy at a particular pressure.
"Miles are used to measure driving distances and only driving distances…
Not only. Four minute mile. Ironman Triathlon open water swim and bike ride. Borders of the District of Columbia.

That said, I agree with you about the points of reference thing.

OK, I should have said distances involving travel.
The point is, since no one uses miles to measure things normally measured in inches or feet, the fact that a mile is not some X 10 multiple of these units is of little consequence.
Similarly, since diamonds are only compared to other diamonds, nobody cares how many carats make up a ton or an ounce.

Another example of ‘reference point’ is using feet per second to compare bullet velocities. Tell me that a new rifle caliber shoots a bullet 2000 miles per hour and I would have to mentally convert that to feet per second in order to have an idea of whether it is more or less powerful than a .30-06. Even though miles per hour is not a metric measurement, it may as well be a metric measurement for me when used to measure bullet velocity.

Edited my post above for tone. DC borders don’t involve travel, they’re limits laid out in the Constitution (of course there was a change when some territory was retroceded to Virginia). Still agree with you about reference points. But I also see the value in learning both systems, metric and English and gradually changing signage to reflect km and mi. The real problem is the appalling number of people who can’t multiply by .6 or 1.6 .

Joseph, while I agree that the metric system is more logical, the barrier to conversion is the enormous amounts of money it would cost to convert the machinery, tooling, design documentation, manufacturing documentation, and standards in the manufacturing industry.

Take a look at your own tool box. I’d bet you have a mix of metric and the US stuff, even. I have found both fittings on the same car.