What's a Gallon? | Hacker News Reader

What's a Gallon?

grr.crankybill.com

30 pointsbillpg60 comments

Aside from the occasional crashed Mars lander, technical people in the U.S. get along quite fine thinking in the units best suited to the task at hand. I develop film in my apartment, and I use metric units while developing black and white but conventional units while developing color slide film — because the processes are documented in those respective units.

I don't know what kind of car Cranky Bill is driving, but if it's new enough, chances are he could crack the manual and figure out how to switch it to display values in liters/100km. My motorcycle does that, and my last car did it. I set my motorcycle to display temperatures Celsius, speeds in whatever the local country's unit happens to be, and fuel efficiency in mph.

Also, he might just look up the stats for his car on the Internet.

Bill sure is cranky.

The pervasiveness of computers, phones, and the internet has all but eliminated the majority of the benefit of switching to metric in America anyway.

In 1978, I'm sure it saved countless hours of calculation and conversion. But in 2019 calculation and unit conversion is a task for computers and not people, and for computers it makes no difference.

I think it'd actually save more resources to focus on other forms of standardization. Maybe the UK could drive on the right side of the road, for example. Or maybe they could ditch their arcane electrical plugs for the European or American standards. These changes would save a tremendous amount of localization waste.

I'd like to offer a friendly early warning of the ... debate you're about to encounter with your description of our vastly superior electrical outlets and plugs as "arcane".

Arcane isn't a judgment on value. You could use the word "rare" instead if you like.

It totally is and if you'd ever stood on one you'll know how magnificently sturdy they are.

I could totally live with Schuko instead of BS1363. A lot of earlier standards in Europe were crap, but Schuko does more or less everything BS1363 does, and at 3.5kW instead of 3kW.

I could probably be argued around to the French alternative to Schuko, I think Schuko is better, but the French way (and the plugs that accept either but not other crap systems) isn't terrible.

I asked the people at Nissan and I was told it wasn't possible to switch it to miles-per-litre. Although I do suspect the person I spoke to had no idea what I was going on about.

But could you change it to km-per-litre?

Litre-per-100km is the European standard.

Dimensionally, that has units of area, and so could be expressed in hectares. My car is getting about 11.5 pico hectares.

The same way that torque has the dimensionality of energy and can be measured in joules.

> technical people in the U.S. get along quite fine thinking in the units best suited to the task at hand.

Is this to say that Imperial units have some intrinsic advantage over Metric in some places? Because to me, it seems like it’s just easier to use one set of units.

Ever try dividing a meter or liter into thirds?

Yes, I seem to recall getting 333 1/3 milliliters, which is usually rounded as 330ml in most contexts.

I don’t see how this is any more of an issue than trying to calculate, for example, one-third of a mile (586 2/3 yards) or one-third of a gallon (1 1/3 quarts, 2 2/3 pints or 42 2/3 fl oz.)

>...technical people in the U.S. get along quite fine thinking in the units best suited to the task at hand.

More like technical people in the U.S. get along quite fine thinking in the units traditionally used for the task at hand. I'd much rather actually use the units best suited for the task, which tend not to be imperial.

What are these tasks that were traditionally performed in customary units in the U.S. — and continue to be done in them — but are more suited to SI units?

An important obstacle to my psychological well-being as an engineer is the failure of humanity to adopt UTC for use on their wall clocks, a failure that has little to do with America's metrical intransigence.

I live in the UK and have my car set to litres per 100km - it's so much easier, if I know my car uses 5L of fuel per 100km travelled and I need to drive 300 miles(500km) down to London I instantly know that I'll need about 25 litres of fuel to complete the journey. Knowing that petrol is about £1.30/litre also gives me an instant estimate of the cost of such journey.

The same thing with MPG: 5L/100km is about 56mpg, so for the same trip to London we'll need about 5.5 gallons. Which is great to know except that I have no idea how much is a gallon from the top of my head. I have to Google it, apparently it's about 3.7 litres? But....that's not right, the figure is now different. Ah. US vs UK Gallon, and of course Google shows me US Gallon as a result for gallon, despite knowing I'm in UK. Imperial gallon is 4.5L and now we arrive at the same number of 25L for the trip.

It's not impossible, I just find the first way much easier to work with.

It's easier if the pump sells in liters, which is not true in the US.

You have 20 gallons, and 20MPG gets you 400 miles, that is an easy calculation. All you have to do is to throw away all the metric unit.

20MPG?! You must be driving an American car. ;)

I drove my parents farm truck for a couple of weeks to commute because my car had broken down and boy was that expensive. 12 mpg if I remember correctly. The gas pump at the station would stop at $100 and the tank wouldn't be full.

LOL, it sounds like you're driving a semi to work.

Yeah it's a RAM1500 with V8 hemi engine, tbh, it almost never hit 20 mpg.. It occasionally hits 19mpg if I'm driving interstate

Well of course, but the article was specifically talking about the madness that is the fact that all UK fuel stations sell fuel in litres, but all cars have their fuel consumption advertised in miles per gallon, even though gallons aren't used anywhere in the UK for anything except for this, and your average < 40 years old person will have no intuitive understanding of how much a gallon actually is.

But UK is full of nonsense like this, kilograms are commonly used for everything, but human weight is given in stones(wtf is a stone), metres are again a common unit, but somehow kilometres for distances aren't. Your own height is given in feet and inches, and my satnav when set to miles gives me turn directions in.....yards(wtf is a yard). I have never heard anyone use yards for literally anything ever in the UK. With furniture/room sizes all dimensions are given in milimetres and centimetres but you'd commonly say you cracked the window open by an inch. Cars use miles per hour for the speedos, but trains use kilometres per hour.

I think I could keep going on and on and on about this.

Much better would be selling fuel in kilograms because summer liter and winter liter are two quite different quantity of fuel.

Serious question: why hasn't the UK switched to km yet? Everything else is metric/decimal now, it seems really weird to get stuck on this one last relic.

I still meet people who argue that pre-decimal currency was better. (20 shillings in a pound. 12 pence in a shilling.)

12 ist a fantastic number for doing maths in your head. 12 divides easily by 1, 2, 3, 4 and 6.

Have you considered joining the Dozenal Society?

http://www.dozenal.org/

I think the more important difference than miles or km is which is the denominator and which is the numerator. The rest is just some multiplication factors.

As another poster pointed out, using [fuel]/[distance] (like l/100km) means I can easily estimate how much gas I need given my decision on where I'm going. Using [distance]/[fuel] (like miles per gallon) is only useful in a situation where I've filled my tank up and ask "Now where could I get to with all this fuel?". I don't think that happens very often.

I suppose it might also be useful in a situation where you're low on fuel and asking "oh Jesus, can I make it to a gas station?", but most cars now have a "[distance] to empty" display on the dash anyway.

Here in Australia, we still talk about 44 gallon drums, which are equivalent to the 55 gallon drums of the USA variety. Both Miles per Gallon and Litres per 100 Kilometres are still used in various ways.

The gallon is approximated by 4.5 litres and the mile is approximated by 1600 metres as simple conversion factors. Often we use both centimetres and feet/inches for peoples height.

Over the years, there have been various discussion amongst friends as to why Americans have this penchant for speaking in feet, pounds and gallons? Sometimes, it has been concluded that Americans like big numbers, so the use pounds instead of tons (or tonnes), etc. We have discussed, at times, why Americans used a smaller grouping system that increased by factors of 1,000 instead of 1,000,000 when using billions, trillions, etc. So you get the discrepancy at times of trying to determine whether someone who is using billion is talking about 1 million million or 1 thousand million.

Much as metric can be difficult to get used to with its basic sizes, it is at least consistent in being based on the count of 10 and having a common set of prefixes for size changes.

No but seriously, what is a gallon?

So obviously you've read the Wikipedia article[0], so beyond that, what are you actually asking?

[0] https://en.wikipedia.org/wiki/Gallon

When a car in the UK lists fuel consumption in miles per gallon, are they using US or imperial gallons?

Imperial gallons, I would wager that most British people aren't aware that the US gallon is different.

What kind of car is it? If it was an American car, I might expect it's US gallons.

My data in the UK is nearly 20 years out of date, but historically most American car manufacturers that sold cars in the UK made market specific models. Ford is a great example of this.

Even if you sell the same model, you are already making significant changes for the driver side being mirrored...

I think the difference in the gallon size has often been used, wittingly or otherwise, to exaggerate the poor gas mileage of American vehicles (the "yank tank" trope in British culture)

But the US Gallon is currently in everyday use. The Imperial Gallon hasn't been used for decades, having long since been replaced by the litre for fuel purchases.

But the US gallon has never been used in the UK, and there is a temporal continuity of usage in mpg, people like to compare across time, a discontinuity would be weird

If a salesmen is telling you a mpg number it's imperial gallons because then the number is smaller and it sounds better.

Looks like different liquids can have different sizes of gallon. (Interestingly, the US "standard" gallon is the same as wine gallon.)

I learned this when I was about five years old:

A cup is 8 ounces. Two cups in a pint, two pints in a quart, four quarts in a gallon. In other words, 128 ounces. This is of course for U.S. gallons.

A lot of things now measured in the metric system are still based on the standard U.S. system, just converted to metric. This is, for example, why whisky comes in 750 ml bottles instead of (say) one liter bottles. It was traditionally sold in fifths (of gallons); i.e., 25.6 ounces, which converts to 757.1 ml. It's also why there are track events of 100 meters, 200m, 400m, 800m, and 1600m. They are near the distance of the old races, and it seems especially noticeable to me for the half mile and mile, probably because I ran those races when I was a teenager.

Thankfully there's almost zero chance the U.S. will convert to metric in my lifetime. I can feel miles and gallons and Fahrenheit in my bones. Metric, not so much.

Or if you're a binary geek like me, 1 gallon = 2^7 ounces.

The standard running race is 1500m, which doesn't make any kind of sense.

Well conveniently the one thing everybody agreed on is that it's some amount of litres.

They don't agree how many, but they did all give up on trying to define it any other way than via SI units like the litre (the US gallon is defined in cubic inches, but its inch is defined in metres so that gets you back to litres).

The even better news is that the litre is defined in terms which you can use for yourself from first principles. So you can thus find out what a gallon is!

First build a Caesium atomic clock, it will need to be cooled to as close to 0K as you can get. This will allow you to determine a second. Now, in a vacuum, or as close to one as you can get, measure how far light travels in this second. This will enable you to determine a metre, you can use this metre to determine a litre of volume and then apply the definition of a gallon.

All previous standards for the gallon relied on prototypes, a government owned "the gallon" or "the inch" and you could only have a copy, at best. But the litre is something you can just determine for yourself the same way you could work out Pi. Unlike a prototype "gallon" or "inch" Caesium atoms are found all over the universe and you can make your own (Kids: Do not try to make your own Caesium at home) and light is readily available or can be made too. Like estimating Pi, the more effort you put in, the closer to exact your approximation will be. Unfortunately even a poor approximation of the litre is harder to achieve than a one digit approximation of Pi, but it isn't impossible.

It is an accessibility layer for SI units.

When I go into a bar in Australia and order a beer it is whatever the locals call it. A pot, a schooner, a pint. In most states a pint is 570ml which is about a 20 fl oz UK pint. Except in one where it is a bit less than a 16 fl oz US pint at 425ml so you have to ask for a real pint. It doesn't really matter because beer isn't traded across borders in pints. For science and commerce you can't afford the confusion over all these local units. But for ordering beer it doesn't matter. No issue with US sports using customary units. I use them all the time for height and sports in a country that has been metric for decades. But when science commentators or NASA use them I cringe hard.

An obsolete measurement of volume.

Only a few countries are too immersed in their self-centred past to use the world-wide metric system.

That refusal to progress has cost millions (billions?) when different units have been used without conversion.

http://edition.cnn.com/TECH/space/9909/30/mars.metric.02/

personally I think we should switch to Planck units.

While that could be more consistent, the presence of all those zeroes would inevitably lead to too many typographical errors.

That's why we'll record them in base 97. Much more compact, therefore easier to read.

That would fix the problem of time zones. All times should be in planck units with the zero epoch at the moment big bang.

It would not fix the problem of time zones. It would just change their interpretation, and maybe their name. As long as we live on a spherical planet with just one sun, and keep our sleep cycles roughly synced to daylight, we will need time zones or something equivalent.

Always remember: There are two types of countries in the world.

Those that use the metric system ...

And those that have gone to the Moon.

There are only two types of countries in the world. Those that lost the ability to launch people into space and those that adopted SI units.

I do remember the Liberian moon landings.

I've always loved the American aphorism: "a pint's a pound the world around" .... which is only actually true in the US, but does show an insight into a certain world view

But a (British/Imperial) gallon is 10 pounds. 20 fluid ounces to the pint.

That's kind of my point, only the US uses US gallons, and only US gallons weigh a pound, but they use this saying that's untrue, but few people notice because the US is a very inward looking culture

The Imperial system of units is useful in lots of scenarios, and it's worth giving a try. You shouldn't judge a person's choice of units until you've walked 1.6 kms in their shoes.

It’s interesting that the widely used units gallon and barrel (as in oil measurement) are both of uncertain etymological origin.

Almost more interesting that the article - this is the third time it has been submitted. The first two died at 2 and 1 points, but while I write, the third is at 17 points. I guess the third time is the charm.

What was different with this submission? Time of day? The other stores that were new at the same time?

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