FWIW - km to miles conversion factor on a four-banger calculator


...or when you HP lacks this conversion factor and you don't remember it (1.609344).

Enter 45 then press the SQRT key three times and voilà:


The error when converting the distance from the Earth to the Moon is than then one mile and a half.

When converting greater distances such as the Earth-Sun distance you might want to subtract 1/450 from 45 before extracting the eighth-root:


The error will be inferior to half a mile.

My 2 cents (every time someone uses this to convert km to miles :-)

Edited: 17 Oct 2011, 7:41 p.m.


That's pretty funny!

And easier than doing (0.3048m per feet ) 5280 feet per mile etc.


I just use eight fifths as the conversion factor.
Much larger error but easy to remember :-)

- Pauli


Driving in Europe I found KM a much more usable distancce measure. I liked the 100M posts along rural roads. A mile is simply too large for my measuring stick. Are we ever going to get on the world standars? Sam


Who wants centimeters when you can have an inch?
Who wants kilometers when you can have mile?
Who wants kilograms-force when you can have pound?
Who wants kilograms when you can have slugs?
Who wants deciliters when you can have cups?
Who wants cubic decimeters when you can have pecks?

And finally, wouldn't you miss chains, rods, furlongs and leagues not necessarily in that order?

See what I mean :-)


Bill; did you realize that 10 chains equal one furlong? And that 100 links are one chain? We have the beginnings of a new metric here. All we need is something that's 6.6 feet (let's call that the basketball player), the 6,600' furlongic mile, and the micro-furlong for fine work.

We have surveyors, horse lovers, cricket players, and all those desirous of knowing just how big "hells half acre" really is - all firmly on our side. We can't loose.

It can't be any more contrived than the metric system.



Shall I quote Mikhail Gorbatchov?


I just use eight fifths as the conversion factor.
Much larger error but easy to remember :-)

I use the same factor and some tricks to convert between miles and Km in my head. Use these to make friends and get dates (well, make friends anyway... nerdly friends).

The trick is knowing that to get 0.6X you take half of X and add 1/10th X. So 0.6*52 = 26 + 5.2 = 31.2

mi->km: multiply by 1.6. So 52mi = 52+26+5.2 = 83km

km->mi: multiply by 0.6. So 52km = 31.2mi.


Which is close to the golden ratio of 1.61803399



Which is halfway between 8/5 and the golden ratio.



But I thought the definition of a four-banger was that it had only the primary four arithmetic operators. So, no square root key. :-)

About 100 lbs ago I used to run 5K and 10K races. So I always remembered 10K ~ 6.2M.


Oh! You are right! It is a 5-banger. Also known as an Audi.


But I thought the definition of a four-banger was that it had only the primary four arithmetic operators. So, no square root key. :-)

About 100 lbs ago I used to run 5K and 10K races. So I always remembered 10K ~ 6.2M.

Yes but I recall there is also a clever iterative way to do square root approximations on a 4-banger. But I forget what the trick is.

And then it would have to be done 3 times. Sort of a mathematical Rube Goldberg process I suppose.


About 100 lbs ago I used to run 5K and 10K races. So I always remembered 10K ~ 6.2M

4 years and 15 kg ago I ran 2400 meters in 10m53s in a proof I had to run the distance in 11m03s at most for a perfect score. I never asked myself why exactly 2400 meters, but I realize now this is approximately one and a half mile.


Clever. In testing the conversion accuracy just for fun) with a relatively large number the nearest calculator I had to hand was a HP39gs and in running the conversion I was reminded that HP got the conversions backwards on that machine. ->MILE converts *FROM* miles to KM and ->KM converts *FROM* KM to Miles.

ROM Version 2.22.




Interesting. What other HP calculators offer direct km->mi and mi->km conversions? I mean without having to append the units as in the 48/49/50g.



WP 34S does it.




It may seem like the long way, but the only distance conversion I've successfully commited to memory is 25.4mm=1 Inch. Being a definition, it is exact. From there, any four banger can get my any conversion I need in just a couple of steps.


I'm not so sure myself. How many links in an atto-parsec? :-)

I love good old imperial measurements, there is an obtuse unit for everything ;-) Well, I love them so long as I don't have to actually use them that is.

- Pauli


I would always prefer the International System, except in situations like the following:

The woods are lovely, dark and deep,

But I have promises to keep,

And miles to go before I sleep,

And miles to go before I sleep.

-- Robert Frost

Here, the metric system would spoil the metric of the poem :-)



Haha very clever!


The woods are lovely, dark and deep,

But I have promises to keep,

Kilometers to go ere sleeping,

Kilometers to go ere sleeping.

No conversion factor will do. This looks quite terrible!


Gerson; how about this??

The woods are lovely, dark and deep,

But I have promises to keep,

And far to go before I sleep,

And far to go before I sleep.

Generic, and still in the correct meter! ;o)


That's better.

Just found this one:


I was just listening to a Bee Gee's song in the car and noticed something even worse: it appears there are no rhymes for kilometer, except speedometer, odometer, magnetometer and the like.

"The preacher talked to me and he smiled,

Said, come and walk with me, come and walk one more mile."

Edited: 18 Oct 2011, 12:47 p.m.


Are you talking about links in a surveyor's (Gunter's) chain or an engineer's chain? I only work in surveyor's chains since I consider engineers chains an abomination.


If you're on a scientific calculator and can tolerate an order of magnitude more error (half a foot in a mile), just use the natural logarithm of 5. You'll be off less than fifteen miles when you get to the Moon.


Weird, I always thought a Mile was 1.852 Km .

As far as I remember, the 2 Miles have already killed!



Patrice, you seem to be talking about nautical miles.


The only one I know about :)


Didn't four-bangers only have the four operations, so no square root? :P



Ciao Cristian,

My definition of "four-banger calculator" matches the one I've found here:

"a calculator that only does addition, subtraction, multiplication and
division – sometimes with square root and percent keys added for good measure."

The greek word for table is trapezi (in a loose transliteration), which originally implied a "four-footed" furniture. Tables now have three, two or even only one foot, yet in Greece they keep on calling it trapezi :-)




As a Canadian engineer raised in both English and SI/Metric systems, I find this post at once funny and coincidentally of interest.

Funny: Upon reading the post, I wondered why one would one bother remembering such complicated numbers when the 'standard' to use is 1 in equals 25.4 mm? It is easy to remember and a breeze to use on a 4-banger.

Interesting: Shortly after reading this post yesterday, I saw an el-cheapo 'scientific 180 function' calculator for $1.50 at Giant Tiger that had the conversion factors listed on the inside cover of the calculator. It said 1 in = 2.53995 cm (or something close to that...). I bought the calculator for my 7 year old and ended up getting if for free as they overcharged me by 100% at the check-out...

I have since researched the conversion factors and cannot find any reference to this bizarre conversion. Any thoughts on this? I do not have the calculator with me.

Jeff Kearns


1 in = 2.53995 cm (or something close to that...)

You have a good memory! That's the same number that appears here and elsewhere.

The exact 2.54 conversion factor derives from the international yard, defined in 1959 as 0.9144 meters (0.9144/36 = 0.0254).

According to Wikipedia, the new international foot "was 2 ppm shorter than the previous U.S definition and 1.7 ppm longer than the previous British definition." However 2.54 cm is about 20 ppm longer than 2.5399 cm, a mistake perhaps.



Edited: 19 Oct 2011, 11:47 a.m.


1 inch (in) | 2.53995 centiliters (cm)



Sharp eagle's sight!

the website you have quoted:

"With a diverse population of over 170 million souls, Brazilians are very happy people, spontaneous, enthusiastic and high-spirited who tend to live for the moment and who know how to enjoy themselves"

They've forgotten to add the following:

and never waste their time by checking and double-checking their websites contents.


Edited: 19 Oct 2011, 1:47 p.m.


I wonder if this relates in any way to the "survey foot" ?

And didn't there used to be some sort of abstruse issue with ml not equaling cubiccentimeters?


Yes. The U.S. Survey Foot was based on the old definition of the meter. So when the meter definition changed, two foot definitions were needed, else all the existing base of survey work would be off.

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