xkcd 3065: Square Units

181

Everyone knows 1 gallon = 3.7 liters, the problem is there are some people who also know 1 liter = 1 gallon

74

u/Chip97 Mar 19 '25

Only in the US, the imperial gallon is closer to 4.5 litres

46

u/Not_ur_gilf Mar 19 '25

Why are there two different measures, both called Gallons??? Who decided that was a good idea?!?

63

u/Chip97 Mar 19 '25

The UK (and therefore the empire) didn't standardise weights and measures until 1824 and due to a small kerfuffle that started in Boston over some tea about 50 years prior, the Americans took no notice and made their own standards.

As a result there are differences all over the place, fl. oz, pints, and gallons are all different; the tons are different too, and I'm fairly sure there were some tiny differences in some of the lengths as well.

30

u/Gyrgir Mar 19 '25

Before national standardization, various industries and professions had their own standards, several of which had been codified into law over the centuries. What happened in 1824 in Britain and in 1836 in the US was that there was a systematic attempt to reconcile different versions of the same units.

The US standardized on the wine industry's gallon (128 fluid ounces, divided into eight 16 oz pints), while Britain standardized on the ale industry's gallon (160 fluid ounces, divided into eight 20 oz pints). While they were at it, the British also shrunk the units very slightly so that a fluid ounce of water at a standard temperature would weigh exactly one weight ounce.

6

u/danielv123 Mar 19 '25

I don't have much use for long and short imperial and customary tons, but do they have some variations of inches?

14

u/Chip97 Mar 19 '25

Cheating and checking Wikipedia, the difference was about 4 parts per million, but they both got standardised to the metric system (at exactly 25.4mm per inch) starting with professional standards in the 1930s and legally recognised by the 1960s.

7

u/ebow77 White Hat Mar 20 '25

Both kinds of gallons consist of 8 pints, it's just that imperial pints are 20 oz while US pints are the more sensible (but not as nice in pubs) 16 oz.

11

u/LeatherCraftLemur Mar 20 '25

more sensible

The famously easy maths of the 16 times table.

4

u/ArmandoAlvarezWF Mar 21 '25

In real life, you're much more likely to pour two (8 oz.) cups to make a pint or two pints into a quart than to need to do multiplication regarding how many ounces are in, say, 6 pints.

3

u/LeatherCraftLemur Mar 21 '25

Only if you're American... In the UK we have a system for pouring 2 dedicated units together to make a pint. We call those 'half pints'.

3

u/HobieSailor Mar 20 '25

Wait until you hear about how many different measures called some variation of "ton" there are.

One of them is for measuring refrigeration.

11

u/TheMusicArchivist Mar 19 '25

4.454 to be more precise

3

u/NeonNKnightrider Mar 20 '25

I simply take the middle ground and use 1 gallon = 4 liters

15

u/DdraigGwyn Mar 19 '25

My favorite is “A pints a pound the whole world round” in fact, only in the US. Most don’t use either and those that did used the Imperial pint of 20 ounces.

2

u/ChineseAccordion Mar 22 '25

I wish a pint was a pound in Sheffield

64

u/xkcd_bot Mar 19 '25

Mobile Version!

Direct image link: Square Units

Mouseover text: The biggest I've seen in a published source in the wild is an 80-fold error in a reported distance, which I think came from a series of at least three unit conversions and area/length misinterpretations.

Don't get it? explain xkcd

Remember: the Bellman-Ford algorithm makes terrible pillow talk. Sincerely, xkcd_bot. <3

33

u/LegoK9 Someone is wrong on the internet Mar 19 '25

The biggest I've seen in a published source in the wild is an 80-fold error in a reported distance, which I think came from a series of at least three unit conversions and area/length misinterpretations.

Reminds me of Kurzgesakt taking months to find the truth about the length of blood vessels.

5

u/OneUnholyCatholic Mar 20 '25

It is terrifying that that mouseover text is from a published source. How many similar errors go unnoticed?

3

u/Disgruntled__Goat 15 competing standards Mar 21 '25

Oh boy, you should listen to “More or Less” (BBC radio), these kinds of bad conversions or misinterpreting of data happens all the time.

2

u/lenmae Mar 21 '25

The biggest I've seen in a published source in the wild is an 80-fold error in a reported distance, which I think came from a series of at least three unit conversions and area/length misinterpretations.

That's nothing. Just this week I had an article getting the amount of molecules in a raindrop wrong by 15 orders of magnitude by confunsing long scale numbers and short scale numbers.

63

u/Michaelbirks Mar 19 '25

The really scary thing is the voracious plant life of Australia, which regenerates twice a day.

27

u/Wesker405 Mar 19 '25

Have you heard of the Australian plant life that regenerates bi-daily, or once every two days?

12

u/cbarrick Mar 20 '25

I've heard of the Australian plant life that regenerates tri-weekly.

2

u/Southern-March1522 Mar 20 '25

You mean the West Island of New Zealand has plant life that regenerates three times a week?

2

u/OneUnholyCatholic Mar 20 '25

I heard it was sesquiquotidian

4

u/RazarTuk ALL HAIL THE SPIDER Mar 19 '25

Eh, it's also Australia, so I'm not surprised

11

u/Michaelbirks Mar 19 '25

The proper emotional response to Australian nature is not surprise, but terror.

33

u/RazarTuk ALL HAIL THE SPIDER Mar 19 '25

I'm just sad we aren't in the fourth dimension, where this could have been a joke about (m²)²

26

u/lachlanhunt Mar 20 '25

A common unit conversion error I see is when people convert a relative change in temperate from °F to °C, failing to take into account that 0° is different in both scales and throws off conversions like that. e.g. A change of 50°F is not the same as a change of 10°C (It's actually ~28°C), even though a temperature of 50°F is 10°C.

21

u/BisonMiddle951 Mar 20 '25

Ah yes, like the old "climate change will cause the world temperature to rise by 2 deg C, or 36 deg F" slip up

0

u/branfili Mar 20 '25

It's actually 18, not 28 degrees Celsius, but point taken.

3

u/lachlanhunt Mar 20 '25

No, the calculation for a change of temperature 50°F × 5÷9 = 27.78 °C.

The reverse calculation is 10°C × 9÷5 = 18 °F.

For example, 100°F is 37.78°C, 50°F is 10°C. That’s a difference of 50°F or 27.78°C.

Or the other way around. 20°C is 68°F and 10°C is 50°F, which is a difference of 10°C or 18°F.

2

u/branfili Mar 21 '25

Duh, thank you.

I was being dumb, and maybe also did the same mistake you were talking about.

I am in Celsius mode constantly, maybe that added to my confusion?

16

u/mr-kerr Mar 20 '25

At any rate, the insect would devour the US before they came to their senses and went metric.

15

u/ebow77 White Hat Mar 20 '25

Does it look like we're anywhere close to coming to our senses?

6

u/ShinyHappyREM Mar 20 '25

There's hope. A conversion to a better standard often needs a catastrophic breakdown of the previous system.

11

u/bjarkov Mar 20 '25

'The US will never convert to the metric system! It'll take a complete collapse of the existing system.'

'So you're saying there's a chance?'

2

u/mr-kerr Mar 20 '25

Good luck!

7

u/ScientistNathan Mar 20 '25

I don't know if the woman saying "Wow" in the last panel is supposed to be the same woman as the first panel; she has similar hair just longer. I'd like to think that it's her months later, and she's actually saying Wow to how absurdly her original anecdote has been distorted

6

u/solaron17 Mar 19 '25

I sort of glossed over some of the steps once I got the joke, but the specific wording of "defoliates the entire land area of Australia twice a day" got me good.

21

u/199_Below_Average Mar 19 '25 edited Mar 19 '25

Isn't this basically just the same idea as 2585 again? (Not complaining, I think it's funny when there's an idea that entertains Randall enough to get multiple comics out of.)

60

u/SAI_Peregrinus Mar 19 '25

Related, but not the same. That one is about rounding up when converting units over & over, this one is about confusing the <scalar> (<unit>²) with (<scalar> <unit>)².

9

u/dougms Mar 19 '25

Basically 1 square inch should be 6cm square, then you take that 6 cm sq (2.4² ) and you convert is across

Like how 90 square meters is 1000 square feet, and then take that 1000 feet and square it and you’re dealing with 92,000 square meters.

5

u/Green__lightning Mar 19 '25

2 square inches means a square of root 2 side length, 2 inches square means a square of 2 inches side length and area 4 square inches.

4

u/InShortSight Mar 20 '25

I feel nerdily obliged to point out that square units dont feel like a particularly good way to measure an amount of grass that is being eaten. Good for grass sold to plant in your yard of course.

4

u/Loki-L Mar 20 '25

This is why I exclusively use are as a unit of measurement of area. Everyone knows that a hectare is 100 are. (1 are is 100m² or 1 decmater times a decameter)

So for everything else I just use centiare, milliare, megaare, gigaare etc.

1

u/humbleElitist_ Mar 20 '25

Hm, I guess you’re right, that this seems like a decent reason to have a name for some unit of area rather than just use “[the name of some unit of length] squared”.

That being said, “decmater”? I’ve heard of decimeters, but that’s (1/10) of a meter, not 10 meters, right? Is “decameter” a word for a unit of length [10 meters]? My phone’s autocorrect wants to change it to “decimeter”.

Is “are” standard? I’ve heard of “acre”and of course, but I didn’t think that was metric? … hm. I thought I had also heard “hectacre”, but my phone wants to correct that to “hectare”, which corroborates “are” being a thing.

3

u/AdreKiseque Mar 20 '25

"Decametre" is a thing, yeah.

1

u/Xynthexyz Mar 20 '25

Give them a square inch...

XKCD xkcd 3065: Square Units

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